Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists.

Astronomy is a field of temporal extremes. Some phenomena—the birth of stars, the ballet of galaxies within clusters, the growth of the Universe—take place over millions or billions of years, timescales too vast for the human mind to easily comprehend. Other events can happen in quick bursts that take you by surprise: Asteroids and comets flash by, a star goes supernova, pulsar beams sweep past at dizzying speeds, an exoplanet whips around a star in just a few hours.

The Vera C. Rubin Observatory is designed to watch it all.

The telescope, funded by the National Science Foundation and U.S. Department of Energy, has been 3 decades in the making, and it just released its first science images. Taken by a digital camera the size of a car in just over 10 hours of test observations, these images captured millions of galaxies and Milky Way stars and thousands of solar system asteroids.

The first look is…wow. Just wow. Take a look:

Named after pioneering dark matter astronomer Vera C. Rubin, the telescope has a 10-year primary mission during which it will create a wide-frame, ultra-high definition time-lapse record of the Universe.

From its perch atop Cerro Pachón in Chile, it will take thousands of images of the Southern Hemisphere sky every night and map the trajectories of millions of asteroids, comets, and interstellar objects in the solar system, enhancing planetary defense efforts. It will record the locations, distances, and brightness changes in distant supernovae, allowing for more precise calculations of the expansion rate of the Universe and deepening our understanding of mysterious dark matter and dark energy. And it might even help conclusively determine whether, and where, a large planet lurks in the far reaches of our own solar system.

And that’s just what we expect to see. Most scientists would say that the most exciting discoveries are the ones that they never even thought of before, the “unknown unknowns.” Humanity has never had a telescope quite like this one, and gosh, we just can’t wait to see what amazing discoveries are just around the corner!

—Kimberly M. S. Cartier (@astrokimcartier.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story idea about science or scientists? Send us a tip at eos@agu.org.

Text © 2025. AGU. CC BY-NC-ND 3.0
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This is an authorized translation of an Eos article. Esta es una traducción al español autorizada de un artículo de Eos.

Los cinturones polvorientos de escombros provenientes del nacimiento de estrellas son extensos y dinámicos, alimentados por colisiones frecuentes entre exocometas y agitados por la gravedad de planetas cercanos, según un estudio reciente publicado en Astronomy & Astrophysics. Los hallazgos ofrecen nuevas perspectivas sobre el proceso de formación planetaria.

Estos cinturones son análogos al Cinturón de Kuiper del sistema solar, una zona con forma de rosquilla más allá de la órbita de Neptuno que alberga cientos de millones de cuerpos helados. Los cinturones de exocometas analizados en el nuevo estudio presentan una amplia variedad de características, incluyendo diferencias en anchura, masa y brillo. Según los autores, estos cinturones probablemente fueron esculpidos por exoplanetas aún no detectados.

“Encontramos que cada cinturón es único, por lo que cada sistema planetario es diferente”, dijo el miembro del estudio, Steve Ertel, un astrónomo del Observatorio Steward y científico principal del Observatorio del Gran Telescopio Binocular, ambos en la Universidad de Arizona. “Pero lo que encuentro más emocionante es que este estudio demuestra, una vez más, que los planetas están en todas partes. Incluso si no podemos verlos directamente, detectamos sus huellas en estos discos.”

Investigadores del proyecto REASONS (Observaciones resueltas de ALMA y SMA de estrellas cercanas) produjeron imágenes de alta resolución de los sistemas de cinturones alrededor de 74 estrellas situadas a aproximadamente 500 años luz de la Tierra, constituyendo la muestra más grande hasta la fecha.

El equipo realizó nuevas observaciones de algunos de estos sistemas utilizando el Gran Conjunto Milimétrico/submilimétrico de Atacama (ALMA) en Chile y el Conjunto submilimétrico (SMA) en Hawái, los cuales son instrumentos sensibles al resplandor del polvo y los pequeños guijarros que conforman los cinturones. Los investigadores combinaron estos resultados con observaciones previas de otros sistemas realizadas con ALMA para completar el conjunto de muestras.

Fragmentación de exocometas

Los cinturones se encuentran a distancias de entre 10 y 100 unidades astronómicas (1 UA equivale a la distancia promedio de la Tierra al Sol) de sus estrellas centrales, una escala comparable a las 30 UA que separan al Sol del borde interno del Cinturón de Kuiper. Estos cinturones se forman a partir de objetos de hasta aproximadamente 1 kilómetro de diámetro, similares a los cuerpos del Cinturón de Kuiper y a los cometas que ocasionalmente visitan el sistema solar interior, razón por la cual se les denomina “exocometas”.

Dichos cuerpos podrían ser restos de los bloques a partir de los cualesnacieron planetas y lunas. En el caso del Cinturón de Kuiper, muchos fueron lanzados lejos del Sol por la gravedad de esos planetas recién formados.

“En las regiones donde observamos estos anillos fríos, se cree que los cuerpos están compuestos por grandes cantidades de hielo, además de material rocoso o polvo”, explicó Ertel. “Cuando estos cuerpos colisionan, se fragmentan en piezas cada vez más pequeñas, y eso es lo que observamos como polvo”.

Este polvo proporciona “perspectivas importantes sobre los sistemas planetarios subyacentes”, señaló Ertel, ya que, al igual que en el Cinturón de Kuiper y el cinturón de asteroides de nuestro propio sistema solar, las propiedades de estos cinturones están estrechamente relacionadas con las órbitas y masas de los planetas.

Algunos sistemas presentan más de un anillo o banda, sugiriendo la posible presencia de múltiples planetas, mientras que el grosor de ciertos anillos indica que podrían contener cuerpos con diámetros de entre aproximadamente 140 kilómetros y el tamaño de la Luna (cuyo diámetro es de unos 3,500 kilómetros). Aunque estos cuerpos son demasiado pequeños para ser detectados en las observaciones de REASONS, su influencia en la dinámica interna de los anillos es significativa.

“La principal sorpresa probablemente fue el hecho de que los cinturones anchos parecen ser más comunes que los anillos estrechos”, mencionó Luca Matrà, físico del Trinity College de Dublín y autor principal del estudio. “Muchos de nosotros apreciamos la imagen del hermoso anillo de Fomalhaut, probablemente el cinturón de exocometas más famoso. Sin embargo, nos sorprendió mucho descubrir que estos anillos son raros”.

Según Matrà, varios factores pueden influir en la forma y el tamaño de los anillos, incluidos los choques entre objetos dentro de los cinturones, las condiciones iniciales en las que se formaron y las interacciones entre el material de los cinturones y los planetas cercanos, posiblemente como resultado de migraciones planetarias.

Las condiciones iniciales incluyen la cantidad de material disponible para formar los cinturones, la luminosidad de la estrella y el entorno estelar circundante. Una estrella más brillante y caliente debería evaporar hielos a mayores distancias dentro del disco de material a partir del cual se forman los bloques de construcción planetarios, conocidos como planetesimales. Una mayor cantidad de material en el disco primordial podría dispersarse más y protegerse mejor de la radiación estelar, evitando la pérdida de polvo hacia el espacio interestelar. En contraste, si una estrella se formó en un cúmulo compacto, las interacciones con otras estrellas podrían haber limitado el crecimiento de los discos formadores de planetas.

Provocando un poco de entusiasmo

Las migraciones planetarias, en las que las interacciones gravitacionales hacen que los planetas se desplacen hacia o lejos de su estrella, podrían provocar que los objetos se agiten en anillos estrechos, los cuales son comunes en sistemas estelares jóvenes donde se están formando nuevos planetas, como pedacitos de hielo en una licuadora. Este movimiento de agitación podría hacer que los anillos se expandan hasta formar los cinturones más anchos que se observan en la actualidad.

“En nuestro propio sistema solar, es probable que Urano y Neptuno no estuvieran originalmente tan lejos del Sol como lo están hoy, sino que fueron empujados hacia el exterior por Júpiter y Saturno”, explicó Sharon Montgomery, profesora de física en la Pennsylvania Western University en Clarion, quien no participó en el nuevo estudio. “Eventualmente, Neptuno provocó todo tipo de agitaciones en el Cinturón de Kuiper. Así que hubo mucha actividad en el sistema solar temprano, y ahora estamos viendo que ocurren procesos similares en otros lugares. Me parece realmente fascinante”.

El nuevo estudio también indica que las estructuras de polvo pierden tanto masa como superficie a medida que envejecen, y que los anillos y cinturones más pequeños se desgastan más rápidamente que los más amplios. Según los investigadores, ambos hallazgos concuerdan con los modelos de formación planetaria y evolución de discos.

Matrà señaló que el equipo ampliará su investigación mediante un estudio más detallado de algunos de los objetivos del proyecto REASONS. “Tomamos 18 de estos cinturones y llevamos al límite la resolución de ALMA, utilizando la máxima resolución posible para abordar nuevas preguntas cruciales”, afirmó Matrà. Las respuestas deberían proporcionar una comprensión aún más profunda de estas intrigantes bandas de exocometas.

—Damond Benningfield, Escritor de ciencia

This translation by Saúl A. Villafañe-Barajas (@villafanne) was made possible by a partnership with Planeteando and GeoLatinas. Esta traducción fue posible gracias a una asociación con Planeteando y GeoLatinas.

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

An extreme exoplanet has gotten even more extreme in the eyes of astronomers. In mapping the 3D structure of its atmosphere for the first time, scientists have discovered that a high-speed atmospheric jet whips around WASP-121b, an ultrahot gas giant planet. They have also confirmed the presence of titanium in the planet’s atmosphere, solving a yearslong mystery about the planet’s atmospheric chemistry.

“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works—not just on Earth, but on all planets,” said Julia Seidel, an astrophysicist at the European Southern Observatory (ESO) in Santiago de Chile and colead researcher on the discoveries. “It feels like something out of science fiction.”

An ESPRESSO Boost

WASP-121b orbits a star bigger and hotter than the Sun in just 1.27 days, making its atmosphere a blistering 2,085°C (3,785°F). The planet is about 75% bigger but just 16% heavier than Jupiter, a so-called marshmallow planet. As WASP-121b zooms around its star, its low-density atmosphere distorts into the shape of an American or Australian football.

Astronomers have studied this planet extensively with ground- and space-based telescopes since it was discovered in 2016.

The planet is big and bright and easy to see against its similarly big and bright star. That made it an easy pick when astronomers needed to test a new observing mode of ESO’s Very Large Telescope (VLT), a set of four 8-meter telescopes in Chile’s Atacama Desert.

“They wanted to go for a safe choice when trying out the mode. WASP-121b fell into their lap,” said Bibiana Prinoth, an astrophysicist at Lund University in Sweden and colead researcher on the discoveries.

In its new capacity, VLT’s four telescopes combine their observing power and achieve the resolution of a telescope twice the size. That light can then be fed into the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument, which produces a high-resolution visible-light spectrum.

Testing that mode during the instrument’s commissioning phase in 2018, astronomers observed WASP-121b cross in front of its star and imprint its atmospheric spectrum on the star’s light.

When Seidel looked at the ESPRESSO spectrum, she noticed something weird about the spectral lines from sodium. She proposed a second set of VLT observations, which took place in 2023.

“I got my data as a follow-up to the strange thing that they saw completely by accident,” Seidel said.

The researchers homed in on the spectral signatures of iron, sodium, and hydrogen, which were emitted from different depths within WASP-121b’s atmosphere. The planet’s puffiness helped turn its transmission spectrum into a 3D map of its atmosphere.

As a star’s light passes through a planet’s atmosphere, each wavelength of that light penetrates down to a different atmospheric depth, called the optical depth. An element’s strongest emission lines come from the physical depth that matches its optical depth. For planets of average density, those optical depths correspond to roughly the same physical depths, so transmission spectra map an atmosphere in one or two dimensions.

But for marshmallows like WASP-121b, those optical depths are more physically spread out, allowing astronomers to use the transmission spectrum to create a 3D map. Using atmospheric circulation models, the researchers traced the movement of material in three layers in the planet’s upper atmosphere—its “outer whimsical shell,” Seidel called it.

Superspeed Jet and Hidden Titanium

In the deepest observed layer, traced with iron’s spectral signature, the team found that heat flows from the planet’s permanent dayside to its permanent nightside both clockwise and counterclockwise. This behavior is typical for hot gas giant planets that, like WASP-121b, are tidally locked to their star, Seidel explained. In the shallowest observed layer, traced with hydrogen’s spectral lines, the team confirmed the puffy planet’s football shape, which is most pronounced in the outermost layer.

In the middle layer, traced with sodium, an atmospheric jet zips around the planet’s equator faster than the planet’s rotation. The oddity that first caught Seidel’s attention was the atmospheric jet distorting sodium’s well-known spectral lines.

The observation is a first, Seidel said. In solar system planets, atmospheric jets flow through deeper layers, and shallow layers dominate heat transport. For WASP-121b, “it’s flipped, and that’s weird, and we don’t know why.”

What’s more, the jet accelerates as it travels across the planet’s dayside, speeding up from 14 kilometers per second in the morning to about 27 kilometers per second in the evening.

“We have given it to the theorists, and they have to fix it now,” Prinoth joked.

That the upper and lower atmospheres flow so distinctly suggests that different mechanisms drive wind in each layer, said Elspeth Lee, an exoplanet climate modeler at the University of Bern in Switzerland who was not involved with this research. “This has been suggested in previous 3D atmospheric modelling efforts…but these observations provide much needed observational evidence of this phenomenon and provide guidance as to where 3D models require future improvement.”

The observations also revealed that WASP-121b’s atmosphere contains titanium, which is known to shape the temperature and pressure structures of hot Jupiter atmospheres. Astronomers have debated for years whether WASP-121b has titanium—some telescopes could see it, whereas others could not. Prinoth explained that the signal from titanium was weaker than they expected it to be, which might explain conflicting past reports.

“There must be some mechanism that depletes it from the atmosphere or from the gas phase,” Prinoth said.

“This new [VLT] capability allowed a much deeper dive into the atmospheric composition and dynamical structure of WASP-121b, a canonical and well-studied ultrahot Jupiter, than ever before,” Lee said. This is also the strongest evidence yet that WASP-121b’s titanium exists and is just trapped deep within the atmosphere, “hiding it from being detected at expected levels,” she added.

These results were published in Nature and Astronomy and Astrophysics.

These observations of WASP-121b push the boundaries of what current telescopes and atmospheric models can map within exoplanetary atmospheres, Prinoth said. Prinoth, Seidel, and their colleagues plan to use the new VLT observing mode to study planets a bit smaller than WASP-121b and those on peculiar orbits.

Those observations will help astronomers prepare for the next generation of giant ground-based telescopes, like the Giant Magellan Telescope or ESO’s upcoming Extremely Large Telescope (ELT), which will provide even higher resolution spectra and enable this kind of 3D atmospheric study of planets that more closely resemble Earth.

“These two studies pave the way for a super promising ELT era of exoplanet atmosphere characterization,” Lee said.

—Kimberly M. S. Cartier (@astrokimcartier.bsky.social), Staff Writer

Citation: Cartier, K. M. S. (2025), First 3D map of exoplanet weather reveals superfast jet, Eos, 106, https://doi.org/10.1029/2025EO250103. Published on 17 March 2025.

Text © 2025. AGU. CC BY-NC-ND 3.0
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Dusty belts of debris from the birth of stars are wide and dynamic, fed by frequent collisions between exocomets and stirred by the gravity of nearby planets, according to a recent study published in Astronomy & Astrophysics. The findings offer new insights into the planet-building process.

The belts are analogous to the solar system’s Kuiper Belt, a doughnut-shaped zone beyond the orbit of Neptune that holds hundreds of millions of icy bodies. The exocomet belts analyzed in the new study show a wide range of characteristics, including different widths, masses, and brightnesses. The belts were probably sculpted by unseen exoplanets, the authors conclude.

“We find that each belt looks unique, so each planetary system is different,” said study member Steve Ertel, an astronomer at Steward Observatory and lead scientist for the Large Binocular Telescope Observatory, both at the University of Arizona. “But what I find the most exciting is that this study shows again that planets are everywhere. Even if we can’t see them directly, we see their signposts in those disks.”

Researchers with the REASONS (Resolved ALMA and SMA Observations of Nearby Stars) project produced high-resolution images of the belt systems around 74 stars within about 500 light-years of Earth—the largest sample to date.

The team made new observations of some of the systems with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Submillimeter Array (SMA) in Hawaii, which are sensitive to the glow of the dust and small pebbles that form the belts. Researchers combined those results with earlier observations of other systems made with ALMA to complete the sample set.

Exocomet Breakups

The belts are found at distances of 10–100 astronomical units (1 AU equals the average distance from Earth to the Sun) from their central stars, comparable to the 30 AU from the Sun to the inner edge of the Kuiper Belt. They are created by objects up to about 1 kilometer in diameter that are similar to bodies in the Kuiper Belt and comets that occasionally visit the inner solar system—hence the name “exocomets.”

Such bodies may be leftover building blocks from the birth of planets and moons. In the case of the Kuiper Belt, many were hurled away from the Sun by the gravity of those newly forming planets.

“Where we observed these cold rings, the bodies are thought to be composed of large amounts of ice in addition to the rocky material or dust,” Ertel said. “When those bodies collide, they break up into smaller and smaller fragments, and this is what we see as dust.”

The dust provides “important insights into the underlying planetary systems,” Ertel said, because, as with the Kuiper Belt and asteroid belt in our own solar system, belt properties relate to the orbits and masses of planets.

Some systems have more than one ring or band, suggesting they might contain multiple planets, while the thickness of some rings suggests they could contain bodies from about 140 kilometers in diameter to the size of the Moon (which has a diameter of about 3,500 kilometers)—too small to be seen in the REASONS observations but large enough to influence a ring’s internal dynamics.

“The main surprise probably was the fact that broad belts are likely more common than narrow rings,” said Luca Matrà, a physicist at Trinity College Dublin and the study’s lead author. “Many of us hold dear the image of the beautiful Fomalhaut ring, probably the most famous exocomet belt. However, we were very surprised to learn that such rings are rare.”

Several factors may be responsible for the rings’ shapes and sizes, Matrà said, including collisions between objects within the belts, the initial conditions in which they formed, and interactions between material in the belts and nearby planets, perhaps as the result of planetary migrations.

Initial conditions include the amount of material available to form the belts, the luminosity of the star, and the nearby stellar environment. A brighter, hotter star should evaporate ices at greater distances within the disk of material from which the building blocks of planets, known as planetesimals, are born. More material in the initial disk could spread out and better shield itself from the star’s radiation, preventing the loss of dust to interstellar space. If a star formed in a tight cluster, on the other hand, interactions with other stars might limit the growth of planet-forming disks.

Stirring Up Some Excitement

Migrations, in which gravitational interactions cause planets to move toward or away from their star, could whip up the objects in narrow rings, which are common in young star systems where new planets are being born, like ice chips in a blender. That stirring motion could cause the rings to spread out to form the wider belts seen today.

“In our own solar system, Uranus and Neptune probably originally weren’t as far from the Sun as they are today, but they got pushed outward by Jupiter and Saturn,” said Sharon Montgomery, a physics professor at Pennsylvania Western University in Clarion who was not involved in the new study. “Eventually, Neptune created all kinds of stirring in the Kuiper Belt. So there was lots of excitement in the early solar system, and now we’re seeing the same sorts of things happening elsewhere. I find that really, really fascinating.”

The new study also indicates that the dust structures lose both mass and surface area as they age, with smaller rings and belts depleted more quickly than wider ones. Both findings are consistent with models of planetary formation and disk evolution, according to the researchers.

Matrà said the team will expand its work through a more detailed study of some of the REASONS targets. “We took 18 of these belts and pushed to the limit of the ALMA resolution, going to the maximum possible resolution to ask pressing new questions,” Matrà said. The answers should provide even deeper insights into these intriguing bands of exocomets.

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2025), Dusty belts provide clearer insights into exoplanet formation, Eos, 106, https://doi.org/10.1029/2025EO250067. Published on 18 February 2025.

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In 2021, a network of ground-based telescopes scanning the sky spotted a Sun-like star dimming rapidly. An amateur astronomer looking at the same system in data from NASA’s now-decommissioned space-based NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) telescope noticed that it had brightened by 4% at infrared wavelengths just a few years before.

Upon closer inspection, researchers proposed that the brightening in 2021 was the emission from two planets colliding and creating a new planetary body. The ensuing dimming was likely due to postcollision dust and debris passing in front of the star, named ASASSN-21qj.

Now, with new data collected in February and November with the James Webb Space Telescope (JWST), researchers can start to understand what happened after the collision.

A Lucky Spot

The original observations of ASASSN-21qj came from sky surveys, which are conducted by networks of telescopes that scan large portions of the sky regularly. That’s a lot of sky to sift through, so catching this collision was a matter of chance, said Simon Lock, a planetary scientist at the University of Bristol and a study coauthor. The Las Cumbres Observatory Global Telescope Network captured images in visible light, and the Wide-field Infrared Survey Explorer observed the system in the infrared.

“We’ve never directly observed something like this before. We’ve seen bits like the debris passing in front of stars. We’ve seen disks of material suddenly get a bit fatter and hotter, but actually to look at the direct emission from a newly formed planet, that’s really cool,” Lock said.

There are several theories for how planets are formed, and these findings seem to support the hypothesis that they are formed through the collision of other celestial bodies, Lock said. Given the size and temperature of the event, one possible set of circumstances is that the colliding bodies were Neptune-sized ice giants.

After the team realized what the sky surveys had accidentally observed, they followed up the detection with observations from JWST. But the JWST infrared images and spectra of this system have been challenging to interpret, Lock explained, in part because the signal they are searching for is so faint in comparison to the whole system, especially the star.

The observations capture the star, a postcollision body, and potentially a dust cloud, said Richelle van Capelleveen, a doctoral candidate studying planetary science at Universiteit Leiden and a study coauthor. “It’s been quite a challenge to properly subtract the star off of the combined spectrum,” she said.

Astronomers have encountered this challenge before, for example, with direct observations of exoplanets, but in this case, the signal was even fainter than expected. The team thinks the reason is that the postimpact body cooled faster than models predicted.

What’s more, some parts of the spectrum returned by JWST are more intense in the November data than in the February readings, whereas others are less intense, Lock said. This behavior doesn’t match what astronomers would expect from rapidly cooling postcollision material. Though there are more calculations still to be run, the initial results indicate to Lock that there is something happening in this system that doesn’t fit with our current understanding.

“It really is that we’re at a point of not knowing, and that’s quite exciting as a scientific point, but it’s also kind of terrifying,” Lock said. He added that he is hoping that with input from more experts they can decode what could cause the unexpected readings. The team will receive more Webb data in June.

The researchers presented their findings on 9 December at AGU’s Annual Meeting 2024 in Washington, D.C.

A Not So Unique Event?

The uniqueness of this observation is a weakness, said Jack Lissauer, a planetary scientist at NASA’s Ames Research Center who was not involved in the study. Statistically, researchers can’t learn much from a single observation, he said. “Part of the problem with one [event] is when you are looking for a lot of things, you’re going to find some unusual things,” Lissauer said.

Right now it’s difficult to assess whether events like these are happening frequently, but from a theoretical standpoint, this type of event is expected, said stellar astrophysicist Carl Melis from the University of California, San Diego. Melis was not involved in the original paper but is now helping with further exploration.

The search for historical examples of this type of collision could help solidify the implications of these findings, said Matthew Kenworthy, an astronomy professor also at Universiteit Leiden who has been involved in this finding from the beginning.

“There’s plenty of evidence that violent interactions happen,” Kenworthy said. “To see one of these things actually caught in the act is pretty spectacular, and currently, it’s only one of them, but we discovered it by a very, very wonderful accident. Now we know what to look for. In fact, our suspicions are quite strong that this isn’t the only thing out there.”

—Marta Hill (@martajhill), Science Writer

Citation: Hill, M. (2024), Telescopes catch the aftermath of an energetic planetary collision, Eos, 105, https://doi.org/10.1029/2024EO240581. Published on 20 December 2024.

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The outer layers of most stars are like a pot of boiling water, with giant bubbles known as convection cells transporting energy and hot gases from deep inside the star to the surface. Bubbles on the Sun are as big as Texas, and they percolate to the surface and fall again over a period of a few minutes.

Astronomers have now measured both the size and cadence of bubbles on a star other than the Sun for the first time. The star, R Doradus, is a red giant roughly 350 times the Sun’s diameter. Its convection cells are dozens of times the size of the Sun itself, and they rise and fall over a period of a few weeks. These data should help theorists revise models of the final stages of life for the Sun and similar stars.

“This result isn’t a big shock, but it’s very pleasing,” said Christopher Sneden, an astronomer at the University of Texas at Austin who wasn’t involved in the study. “It’s especially interesting because they caught an ordinary, garden-variety star,” which began life with a mass similar to the Sun. “It’s not some exotic, ‘Betelgeuse is going to explode any minute folks, run for your lives!’ kind of star. And that’s what makes this study especially welcome.”

A Mighty Big Target

Researchers were studying how dying stars eject elements created through nuclear reactions in their cores into the interstellar medium. “We are all made of ‘stardust,’ and much of the material around us is made in stars,” said Wouter Vlemmings, an astronomer at Chalmers University of Technology in Sweden and the study’s lead author. “How this material is ejected from old stars to be incorporated into new stars and planets is still not completely clear.”

R Doradus was a primary target because it is relatively close—roughly 180 light-years away—and quite large. It spans about 3.3 astronomical units (1 astronomical unit is the average distance from Earth to the Sun), so if it replaced the Sun in our own solar system, it would engulf the four innermost planets, including Earth. The combination makes R Doradus one of the largest stars in the sky.

R Doradus is so big because it has evolved into an asymptotic giant branch star—the final and most impressive red giant phase—as nuclear fusion shut down in its core. Today, R Doradus is fusing hydrogen and helium in thin shells around the core. Radiation from these reactions pushes on the surrounding layers of gas, inflating the star.

Despite its great expanse, R Doradus is only slightly less massive than the Sun. It probably began life no more than 1.25 times the Sun’s mass, so it gives us a preview of what the Sun will look like when it enters its own red giant phase in about 5 billion years.

The astronomers observed R Doradus with ALMA (Atacama Large Millimeter/submillimeter Array), a telescope high in the Andes Mountains of Chile, during five sessions spaced roughly 1 week apart in July and August 2023. ALMA’s high resolution allowed the team to map motions at the star’s millimeter “surface.” (Optical and shorter wavelengths can see slightly deeper into a star’s atmosphere, so “there is not a single surface that can be defined,” Vlemmings said.)

The observations revealed convection features up to 0.72 astronomical unit in diameter—more than 75 times the diameter of the Sun. “The size corresponds well to the expectation of convection cells on these types of stars, so that’s what we think we’re seeing,” Vlemmings said.

Bubbling Faster Than Expected

Though previous studies have imaged convection cells on a few large stars—mainly red supergiants such as Antares, which are much more massive—the R Doradus study was the first to measure their velocity. It showed that the cells were moving faster than expected, bubbling up and falling away on timescales of 3 weeks to a month.

“This is the first time the timescales of convection can be measured [anywhere] except for the Sun,” Vlemmings said. “But based on theoretical extrapolations from the Sun, we were expecting the timescales to be 3 to 4 times longer.”

So far, the astronomers have no explanation for the discrepancy. They hope to learn more, however, through continued analysis of the R Doradus observations and those already made of two other stars, along with future observations of a few other target stars.

“I’d love to see this kind of observation for another star,” Sneden said. “If you see this behavior in a second star, then you know you’re on track, you know what you’re doing, and you can force the modelers to address this issue.”

Additional modeling could add insights into the next stage for R Doradus and similar stars—a planetary nebula. In this phase, the star will expel its outer layers, briefly enveloping itself in a colorful shell of expanding gas and dust. That will leave behind only a now-dead core, a white dwarf—the fate that awaits the Sun after perhaps a billion years as a red giant.

“One part of me wants to ask if this is the start of a planetary nebula,” Sneden said. “One of the standard ways people wave their hands about planetary nebulae is that there are certain big ‘burps’ from the interior, which eventually puff out even more.” “Eventually” could be millions of years in the future, Sneden said, “but millions of years is short for a star.”

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2024), ALMA watches the surface of a star “boil,” Eos, 105, https://doi.org/10.1029/2024EO240449. Published on 10 October 2024.

Text © 2024. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Just a few short decades ago, scientists were discovering the first planets beyond our solar system. Now, thousands of such exoplanets are known, and researchers are using state-of-the-art observations to probe the chemical compositions of their atmospheres.

A team recently detected hydrogen sulfide—the compound that gives rotten eggs their characteristic stench—in the atmosphere of HD 189733 b, an exoplanet roughly 60 light-years from Earth. This discovery suggests it likely formed via the accretion of smaller bodies known as planetesimals, rather than by collapsing from a cloud of gas and dust, the team suggested.

HD 189733 is a Sun-like star in the constellation Vulpecula (“little fox”), which sweeps high across the summertime night sky at northern latitudes. The star is too faint to be seen with the naked eye, but sensitive instruments attached to large telescopes have no trouble spotting its light. In 2005, astronomers published observations of HD 189733 that revealed the star to be wobbling ever so slightly. That motion indicated the presence of an unseen orbiting planet, which scientists called HD 189733 b.

Like Jupiter, but Not

Researchers have inferred that HD 189733 b is roughly 10% more massive than Jupiter. But unlike Jupiter, which is roughly 780 million kilometers (484 million miles) from the Sun, HD 189733 b’s orbit takes it to within 5 million kilometers of HD 189733.

“It orbits very close to its star,” said Guangwei Fu, an astronomer at Johns Hopkins University in Baltimore and lead author of the new study.

That orbital arrangement contributes to a lucky coincidence: As seen from Earth, HD 189733 b regularly appears to pass directly across the face of its host star. Fu and his colleagues recently exploited those so-called transits to probe the exoplanet’s atmosphere.

By comparing observations of HD 189733 with and without HD 189733 b in front of it, the team measured how starlight dimmed as it traveled through the planet’s atmosphere. Those data revealed the chemical compounds that make up HD 189733 b’s atmosphere. “The planet blocks a different amount of starlight depending on what gas is present in the planet’s atmosphere,” said Fu.

Going to Space

Fu and his collaborators analyzed data from the James Webb Space Telescope. Making observations from space was key, Fu said, because he and his team were measuring near-infrared light (with wavelengths of roughly 2–5 micrometers). Our planet’s atmosphere absorbs strongly in that part of the electromagnetic spectrum, muddling the signal for ground-based telescopes.

The Hubble Space Telescope, also situated beyond much of Earth’s atmosphere, is limited to detecting wavelengths shorter than about 2.5 micrometers. It’s therefore unable to observe the signatures of several important compounds, Fu said. “Carbon dioxide, carbon monoxide, and hydrogen sulfide are all beyond 2–3 microns.”

The researchers started by reconfirming earlier findings that the atmosphere of HD 189733 b contains water. Those observations allowed the team to estimate the abundance of oxygen. However, it’s critical to detect other compounds as well, Fu said. Astronomers refer to any elements other than hydrogen or helium as metals, and measuring an array of metals is important, he said. “You can get a holistic view of what the atmosphere is made of.”

Fu and his colleagues also detected carbon dioxide, carbon monoxide, and hydrogen sulfide. The discovery of hydrogen sulfide on this world is a first for an exoplanet, said Aurora Kesseli, an astronomer at the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena who was not involved in the research.

That’s important because measuring hydrogen sulfide sheds light on the abundance of sulfur in HD 189733 b’s atmosphere. And that measurement, paired with information about oxygen and carbon from observations of carbon dioxide and carbon monoxide, allowed the researchers to estimate HD 189733 b’s so-called metallicity—essentially, its abundance of metals compared with its abundance of hydrogen.

HD 189733 b’s metallicity was a few times higher than the Sun’s and comparable to that of Jupiter. That’s expected for an exoplanet of this mass and radius, Kesseli said. Planets that are more massive tend to have lower metallicities, she said, so this result also jibes with other observations of exoplanets made by the James Webb Space Telescope.

Enter the Planetesimals

Determining HD 189733 b’s metallicity furthermore helps constrain how this planet likely formed. There are two generally accepted models of planetary formation. In one model, known as core accretion, planets are built up over time as smaller bodies—known as planetesimals—collide with one another. In the other, known as gravitational instability, planets form from the collapse of a cloud of gas and dust.

HD 189733 b’s metallicity suggests that it formed from the buildup of planetesimals, Fu and his collaborators concluded in their study, which was published in Nature. Planets that formed from the gravitational collapse of a cloud of gas and dust, on the other hand, tend to have lower metallicities because more hydrogen gets incorporated into those worlds, Fu said.

Fu and his team aren’t finished yet with HD 189733 and its orbiting planet. They’re currently studying other observations from the James Webb Space Telescope obtained at 5–25 micrometers that they hope will reveal the presence of clouds on HD 189733 b. Those clouds, if they exist, will likely be made of silicon, Fu said. “This planet is way too hot to have water clouds.” The James Webb Space Telescope has really revolutionized our study of exoplanets, he said. “It’s been a game changer for exoplanet science.”

—Katherine Kornei (@KatherineKornei), Science Writer

Citation: Kornei, K. (2024), Smells like an exoplanet, Eos, 105, https://doi.org/10.1029/2024EO240341. Published on 1 August 2024.

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Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

The giant radio telescope at the Arecibo Observatory was destroyed twice: the first time deliberately to save the planet, the second time as a result of natural disasters—making it harder to save Earth in the future.

Although the first “destruction” was a special effect in the 1995 James Bond movie GoldenEye, the world’s most powerful telescope for studying near-Earth asteroids was, in real life, damaged beyond repair by multiple storms before finally collapsing in December 2020. For more than 50 years, the Arecibo Telescope (often referred to simply as “Arecibo” when there’s no confusion with the observatory as a whole) was the largest in the world: a radio dish 305 meters (1,000 feet) in diameter set into a natural karst depression in Puerto Rico. It played a part in studies of Earth’s ionosphere, attempts to detect signs of—and send messages to—potential alien civilizations, the characterization of pulsars, and many astronomical discoveries.

The greatest loss posed by Arecibo’s collapse, however, may be the ability to identify potentially hazardous asteroids and comets using radar to track their orbits and other properties. Our solar system contains more than 2,000 known possibly dangerous near-Earth objects (NEOs). The vast majority don’t pose a danger to us for the next century or more, but at the same time, the danger from an asteroid impact is large enough that we want as much warning as possible—just ask the dinosaurs. Radar astronomy is a key part of the field known as planetary defense for that reason.

“Asteroid or comet impacts are maybe the one natural disaster that you can prevent,” said Patrick Taylor, who heads the radar astronomy division of the U.S. National Science Foundation’s National Radio Astronomy Observatory, a research organization that manages several telescope facilities around the world. Though we can’t prevent largely erratic disasters caused by earthquakes, volcanoes, or hurricanes, extraterrestrial rocks follow predictable—and possibly changeable—orbits around the Sun. “If you know about it soon enough, you can think about a mission to it,” Taylor said.

Without Arecibo, the entire world currently has only a single operational radar observatory, and it’s part-time: the transmitter and receiver that make up the Goldstone Solar System Radar at the Goldstone Deep Space Communications Complex in California, part of NASA’s spacecraft communication network. Researchers have big proposals for future radar observatories, most notably the Next Generation Radar (ngRADAR) project at the Green Bank Telescope (GBT) in West Virginia. Meanwhile, the upcoming Vera C. Rubin Observatory in Chile and NASA’s NEO Surveyor spacecraft (which operate in visible and infrared light, respectively) will discover hundreds of NEOs every year, all of which will need follow-up radar observations. The Green Bank Observatory, which houses the GBT, is funded by the U.S. National Science Foundation, as is the Vera C. Rubin Observatory.

The catastrophic loss of Arecibo highlights how much we needed it for planetary defense and how problematic it is to rely on any single observatory for this essential work. Next-generation radar proposals involve multiple telescopes for sending and receiving signals, as well as exploiting modern technology to make it possible to carry on when components fail.

“We’re civilized people, we can have a pretty darn good planetary defense program to spot the objects well in advance,” said Amy Mainzer of the University of California, Los Angeles, who is one of the scientific leads on NEO Surveyor. She argued that we have the technology to do that right now: “There’s nothing here that’s incredibly unusual or requires development of some unobtainium-based material.”

“So Many Dog Bones”

Most telescopes only receive light, whether in optical (visible), infrared, radio, or other wavelengths. Radar actively sends radio light to space, bouncing it off planets, the Moon, comets, or asteroids. As with radar in aviation and meteorology, comparing the radio waves received to those sent allows researchers to measure the position and speed of objects precisely, along with surface details.

“Every other technique in astronomy depends on reflected sunlight or emitted radiation,” said Marina Brozovic, a radar astronomer at NASA’s Jet Propulsion Laboratory. “We bring our own flashlight, and the echo comes back carrying lots of valuable information from super precise measurement of where that object is in space to physical characteristics [like] how fast it’s spinning.”

The time between sending and receiving radio waves reveals the distance, whereas shifts in wavelength provide velocity data. Polarized radio waves—imagine a type of corkscrew motion for the beams—yield information about the surface of the target object, such as its roughness and how metallic it is. And, of course, if the object is large or close enough, radar can produce an image of it, which is especially useful for NEOs, which are too small and fast moving for optical imaging.

“Once an optical or infrared telescope says, ‘Hey, here’s an asteroid!’ if you give me 3 minutes on it with radar, I can nail down its orbit,” said radar astronomer Edgard Rivera-Valentín. Currently at the Johns Hopkins Applied Physics Laboratory, Rivera-Valentín spent 4 years at Arecibo before its collapse. “Optical telescopes don’t get enough data to constrain the orbit without radar, so a lot of the times, we actually lose the asteroid. You don’t want to lose a potentially hazardous object!”

Arecibo pioneered the use of radar on asteroids by measuring the orbit of the large asteroid Eros in 1975 and provided the first direct radar image of Castalia in 1989. Both of these NEOs had been identified using other methods (Eros was discovered in 1898), but radar provided detailed information unavailable other ways. The image of Castalia, for instance, showed it to be a “contact binary”: a peanut-shaped body consisting of two asteroids stuck together or, perhaps, a single asteroid in the process of being pulled apart.

“With radar, [NEOs] are not just a little dot moving in space,” Rivera-Valentín said. “We can tell the entire shape of it: Is it actually spheroidal? Is it a diamond shape? Is it a dog bone? There’s so many dog bones. This one looks like a ghost. This one looks like a skull.”

Radar also has allowed astronomers to identify asteroid moons: smaller bodies separated from and orbiting the main asteroid. By measuring the orbit of these moons, researchers can use basic physics to obtain asteroid mass, which then reveals density and clues about composition.

“One out of six asteroids could be contact binaries, and you can’t really tell those apart from ellipsoidal asteroids just from optical observations,” said Anne Virkki of the University of Helsinki, who formerly headed a radar astronomy research group at Arecibo. She emphasized the importance of getting the shape of asteroids to send spacecraft to study them scientifically or to attempt to redirect them away from Earth. “When you have better shape models, then you can get also gravitational models. It’s very different for a spacecraft to orbit something that’s spherical, or if it looks like this peanut thing.”

From the Cold War to the 21st Century

Amazing as it is, radar astronomy does come with some drawbacks.

One drawback is attenuation, or reduction in signal strength. Light spreads out as it travels through space, resulting in greater attenuation the farther away the source is. Attenuation literally gets radar going and coming: The beam arriving at the target is diminished by the square of the distance; then its return to Earth sees the signal dropping off by the square of the distance again. Ultimately, this means an object twice as far away will have a radar signal 1/16 as strong.

The ngRADAR proposal is designed to mitigate the attenuation problem. The GBT is the world’s largest fully steerable telescope, which means it can be pointed at targets of interest. Beyond updating the telescope’s amplifiers, however, ngRADAR will use the Very Long Baseline Array (VLBA) to receive the returning radar signal. The array consists of ten 25-meter radio telescopes distributed from the Virgin Islands to Hawaii, which act together as a single giant observatory. Using the VLBA will increase the sensitivity of radar observations, mitigating many of the issues with signal drop-off and enabling astronomers to get size, shape, and rotation data from more distant asteroids than before.

Another drawback to radar astronomy is power—a radar observatory requires a lot more power than a normal telescope because it sends signals rather than just receiving them. That problem is compounded by observatories relying on Cold War era technology.

“Arecibo used and Goldstone still use something called klystrons, which are big vacuum tube amplifiers,” Taylor said. To get enough power to do radar astronomy, he added, the klystrons need to be huge: 2 meters (6 feet) tall and weighing hundreds of kilograms (thousands of pounds). To make matters worse, “they’re known to fail catastrophically. You can often lose fifty or even a hundred percent of your capability if they fail,” he explained.

Next-generation radar proposals involve solid-state amplifiers called monolithic microwave integrated circuits (MMICs, pronounced “mimics”), which produce less power than klystrons but are much smaller and more robust to failure. In Brozovic’s analogy, MMICs are like multiple LEDs in your metaphorical flashlight instead of a single halogen bulb: less bright but advantageous in other ways.

“Instead of having one or two big components, you have thousands of [amplifiers] built into a larger array,” Taylor said. “If something breaks, you can pull that out, keep working, replace it, and be back up to speed again.”

Last Telescope Standing

Until ngRADAR or similar projects begin operation, a single observatory is carrying the entire burden of radio astronomy, the lone hero in the breach of planetary defense.

“Goldstone was always complementary to Arecibo,” said Brozovic, who has been performing radar observations there since 2007. “Arecibo was about 15 times more sensitive than Goldstone is. However, we are a fully steerable antenna that covers about eighty percent of the sky. We observe at Goldstone about 50 near-Earth asteroids every year.”

In other words, astronomers can point the telescope at the objects of interest, whereas Arecibo was set into the ground and required its targets to pass overhead. Goldstone demonstrated its responsiveness in 2022, when the Double Asteroid Redirection Test (DART) mission deliberately slammed into the asteroid Dimorphos.

“The radar observations gave us a rough estimate of the [orbit] change less than a day after the impact,” said Cristina Thomas of Northern Arizona University, who was one of the scientific leads on DART. “It was really phenomenal! You know where Dimorphos is supposed to be, and you see it in a different place in the radar observations.”

Goldstone can see more of the sky than Arecibo could, but potentially hazardous asteroids could come from any direction, including regions where the observatory cannot see. For that reason, researchers have begun using the Australia-based Canberra Deep Space Communication Complex, which is identical to the Goldstone dish and also primarily serves NASA spacecraft communications.

However, those two won’t be able to keep up with new NEO discoveries, not least because they’re old. Originally built in 1966, Goldstone will be shut down entirely in 2026 for needed upgrades—leaving Earth completely without a radar observatory.

“You want to have a backup system,” Rivera-Valentín said, adding that the problem isn’t lack of awareness but lack of funding.

The U.S. Congress passed the George E. Brown, Jr. Near-Earth Object Survey Act in 2006, legally obligating NASA to identify every asteroid larger than 100 meters.

“That was supposed to be completed like a decade ago, but it didn’t have the funding and the facilities to make it happen,” Taylor said. “That’s where Rubin and NEO Surveyor are going to come in, but if you don’t follow up [the NEOs] and secure their orbits so that you know where they are in the future, then you just have to rediscover them.”

Mutual Aid for Planetary Survival

When it begins scientific operations in early 2025, the 8.5-meter Vera C. Rubin Observatory will scan a huge swath of the sky, looking for any changes from night to night. Researchers estimate the data could include over a million new asteroid detections within the first 6 months, likely doubling the number of known NEOs, as well as possible hazardous asteroids and comets. NEO Surveyor, slated to launch in 2027, will add even more.

The need for next-generation radar observatories, in other words, could not be greater. At the same time, convincing governments to invest has proven challenging. Scientists in the United States have struggled to keep Arecibo and GBT operational, even with the support of a congressional mandate under the George E. Brown Act. China has proposed building its own radar system that uses arrays of emitters as well as receivers, which, as Taylor noted, might cost as much as building much of the U.S. radio observatory program from scratch.

Pooling resources to make an international planetary defense network would make sense, but that scale of cooperation remains rare in the space industry. In some ways, such dogged independence is as much a Cold War relic as the klystrons: Arecibo was originally designed to assist with ballistic missile deterrence by the U.S. Department of Defense, with scientific applications following later. ngRADAR is being developed in collaboration with defense contractor Raytheon.

“Europe could have its own radar, but the funding is very tricky, because these kinds of telescopes are expensive,” Virkki said. “They need the political will to get them built, which is the hardest part of getting projects started.”

Similarly, Congress balked at rebuilding Arecibo, which is why ngRADAR supporters are taking a different tack in pursuing development.

ngRADAR is “not creating brand new facilities, which makes it attractive to the people who pay for it,” Taylor said. “It gives the Green Bank Telescope and the VLBA another use, potentially bringing in other stakeholders who would be interested in keeping the facilities going.”

Like GoldenEye’s James Bond, the original radar astronomy program was a Cold War relic. Detecting potentially dangerous asteroids is not a job for a single telescope, as the loss of Arecibo demonstrated. The next generations of radar observatories, ngRADAR and beyond, will expand Earth’s planetary defense to give us hopefully enough warning to preserve the world.

—Matthew R. Francis (@DrMRFrancis), Science Writer

19 July 2024: This story has been updated to clarify identified NEOs and Goldstone‘s capabilities.

Citation: Francis, M. R. (2024), Saving the planet with radar astronomy, Eos, 105, https://doi.org/10.1029/2024EO240303. Published on 19 July 2024.

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Source: Geophysical Research Letters

Of all known volcanically active worlds in our solar system—including Earth and some moons of Jupiter, Saturn, and Neptune—the Jovian moon Io is the most restless. Its surface boasts active lava flows, bubbling lakes of molten lava, and more than 400 volcanoes.

Now, Conrad et al. present the highest-resolution images of Io ever captured by an Earth-based instrument. These visible-wavelength snapshots reveal surface features that hint at a recent powerful eruption on the moon and demonstrate the capability of new technology to dramatically enhance monitoring of Io and other worlds in the solar system.

The technology in question, SHARK-VIS, is a new high-contrast optical imaging instrument installed last year on the Large Binocular Telescope (LBT) on Mount Graham in Arizona. SHARK-VIS (System for High Contrast and Coronography from R to K at Visual Bands) mitigates the blurring caused by Earth’s atmospheric turbulence, yielding images that after postprocessing with the Kraken image restoration software, exhibit resolution 3 times that of visible light images obtained by the Hubble Space Telescope. Previously, only spacecraft or Hubble could capture visible light images of Io. But LBT can now capture features on Io’s surface fewer than about 80 kilometers across—comparable to taking a picture of a dime-sized object from 100 miles away.

After installation of SHARK-VIS, researchers used the telescope to observe Io in November 2023 and January 2024. Looking closely at the images, they noticed something curious: A well-known, red-hued, annular ring of deposits from a continuously erupting volcano called Pele appeared to have been partially covered over by other multicolored deposits.

By cross-referencing this information with data previously captured by other instruments, the research team concluded that they were most likely looking at the aftermath of a large 2021 eruption of a nearby volcano called Pillan Patera.

Similar resurfacing events might be commonplace on Io. But with spacecraft visits to the moon being few and far between and only low-resolution images previously offered by Earth-based telescopes, researchers have had scant opportunities to detect them.

SHARK-VIS provides the ability to closely monitor Io’s surface for years to come, allowing a deeper understanding of the moon’s dynamic volcanism. The technology should also enable high-resolution images of bodies throughout the solar system, including other moons, planets, and asteroids. (Geophysical Research Letters, https://doi.org/10.1029/2024GL108609, 2024)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2024), Supersharp images reveal scars of major eruption on Io, Eos, 105, https://doi.org/10.1029/2024EO240278. Published on 3 July 2024.

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Source: Radio Science

Constructed within a natural sinkhole in Puerto Rico, the 305-meter-wide Arecibo Telescope played a part in numerous discoveries, including the first detection of an exoplanet. It was the largest radio telescope in the United States from 1963 until it collapsed in 2020.

However, since 2011, the Arecibo Observatory has also been home to a second, smaller radio telescope. In a new paper, Roshi et al. describe how recent updates to this 12-meter telescope expand possibilities for future discoveries.

The 12-meter telescope originally operated at a relatively narrow bandwidth of radio frequencies, limiting its applications. In addition, its receivers operated at room temperature, which resulted in noisier signals and lower sensitivity compared with telescopes with receivers cooled to cryogenic temperatures.

Now, the researchers have outfitted the 12-meter telescope with a new receiver system that operates at a significantly wider bandwidth (2.5–14 gigahertz) and is cooled to 15°K (˗432°F).

In summer 2023, the newly outfitted telescope demonstrated its capabilities by making a number of space observations. These included detecting methylidyne emission from dark molecular clouds toward the center of our galaxy, observing a previously discovered pulsar, and capturing an image of a region of magnetic activity on the Sun that produces intense solar flares.

With additional improvements planned, the 12-meter telescope at Arecibo could soon contribute to a wide range of future research and educational projects. (Radio Science, https://doi.org/10.1029/2023RS007839, 2024)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2024), Out with the old, in with the cold, Eos, 105, https://doi.org/10.1029/2024EO240115. Published on 28 March 2024.

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Source: Journal of Geophysical Research: Planets

Winter is coming—and not just for Earth’s Northern Hemisphere. Northern summer on Saturn, which completes its orbit around the Sun about once every 30 years, is coming to a close after about 7.5 years, with its fall equinox coming up in 2025.

Just like on Earth, Saturn’s changing seasons are accompanied by changes in its weather. Now, as reported by Fletcher et al., images captured by the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST) show how Saturn’s atmospheric dynamics have evolved since the Cassini-Huygens spacecraft ended its 13-year investigation of the planet in 2017.

Launched in December 2021, JWST set its sights on Saturn in November 2022, with the goal of putting MIRI’s small fields of view to the test against the planet’s large size, rapid rotation, iconic rings, and unusually high infrared brightness compared with MIRI’s other targets. Researchers used MIRI to capture infrared images of Saturn bit by bit and create a mosaic map of Saturn’s northern hemisphere in summertime.

MIRI appears to have passed the test. The images captured the structure of Saturn’s clouds and allowed researchers to measure the spatial distribution of different temperatures and chemicals in the atmosphere, revealing a number of notable seasonal changes.

For instance, the images show that the planet’s north polar stratospheric vortex—a high-atmosphere circulation pattern of gases first detected by Cassini during Saturn’s spring—warmed during the summer; it should cool and dissipate as winter approaches.

The images also highlight a complete reversal of an airflow pattern in Saturn’s stratosphere that Cassini observed during the northern winter. At that point, large quantities of air rose to higher altitudes in the southern hemisphere, crossed the equator, and sank to lower altitudes in the northern hemisphere, enriching the air in gases like hydrocarbons. Now, the MIRI data suggest that air is rising in the north and flowing south, creating a scarcity of hydrocarbons at northern latitudes. This seasonal circulation pattern may continue to change as fall approaches.

Because of MIRI’s exceptional sensitivity and its ability to capture wavelengths of light that Cassini could not, the new images also map the distribution of several gases for the first time, including water in the troposphere and ethylene, benzene, methyl, and carbon dioxide in the stratosphere. The new images also reveal high levels of ammonia at the equator, suggesting that Saturn’s equator may feature processes similar to Jupiter’s, which is also rich in ammonia.

Together these findings provide the first real glimpse into late summertime in Saturn’s northern hemisphere and demonstrate the advanced capabilities of JWST and MIRI. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2023JE007924, 2023)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2023), James Webb Space Telescope captures Saturn’s changing seasons, Eos, 104, https://doi.org/10.1029/2023EO230371. Published on 28 September 2023.

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A distant planet is in a death spiral and is poised to be engulfed by its parent star.

Kepler-1658b is the first inspiraling planet discovered around an “evolved” star—one that has moved out of its prime life. The star—Kepler-1658—is about 1.5 times the mass of our Sun and has expanded to almost 3 times the Sun’s diameter in its late stages of life, earning it the designation of subgiant.

Should Kepler-1658b maintain its current path, it will meet its fate in about 2.5 million years.

As the complicated discovery of the planet and its star has shown, however, nothing is certain. “It’s a very confounding system,” said Ashley Chontos, a postdoctoral fellow at Princeton University and a member of the team that discovered the planet’s shrinking orbit.

Kepler-1658b was the first exoplanet discovered by the Kepler space telescope, which found thousands of bodies over its lifetime using the transit technique. The telescope measured tiny dips in a star’s brightness when a planet crossed in front of it.

Early in its mission, Kepler recorded such dips from Kepler-1658. However, astronomers had initially cataloged the star as belonging to the main sequence—stars like the Sun that are still burning the hydrogen in their cores. Researchers expected the star to be much smaller than it is, so the initial transit signals “didn’t make sense,” said Shreyas Vissapragada, a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics and lead author of the new study. The transit indicated a planet roughly the size of Neptune, our solar system’s third-largest planet. However, the system also produced a secondary eclipse as the planet passed behind the star. At Kepler 1658’s distance, a Neptune-sized planet wouldn’t be bright enough to see, so there would be no evidence of the secondary eclipse.

Kepler-1658b was discarded as a false positive and forgotten about.

That is, until Chontos began looking at vibrations on the surfaces of stars in the Kepler catalog. Because the telescope kept a constant eye on the stars in its field of view, recording brightness levels every half hour or less, it detected “jiggles” caused by sound waves reverberating through the stars. Piecing together the vibrations—a technique known as asteroseismology—revealed details about the stars’ interiors.

In the case of Kepler-1658, they showed that the star was much farther along in life than expected and hence about 3 times bigger. That meant the transiting planet was 3 times larger as well, making it big enough and bright enough to contribute to the system’s overall brightness when it wasn’t eclipsed by the star. “Suddenly, a close-in hot Jupiter made sense,” Chontos said. “That discovery was completely accidental.”

A hot Jupiter is a massive planet comparable to Jupiter—the giant of our own solar system—that orbits so close to its star that it is extremely hot. In this case, Kepler-1658b is about the size of Jupiter, but with almost 6 times its mass. “Even the combined masses of all the planets in [our] solar system don’t add up to that,” Chontos said. The planet orbits its star once every 3.85 Earth days, compared with an 88-day period for Mercury, the Sun’s closest planet.

Changing a Planetary Clock

Kepler observed the system for about 4 years, so it obtained a pretty good, but not perfect, measurement of the orbital period. It appeared to show that Kepler-1658b followed a steady path around the star.

At the same time Chontos was studying the system’s vibrations, though, Vissapragada was conducting his own observations. (One night, in fact, he and Chontos bumped into each other during runs at the 200-inch Hale Telescope at Palomar Observatory, where both were looking at the system.)

Vissapragada obtained data from two Hale sessions plus three monthlong sets of observations by the Transiting Exoplanet Survey Satellite (TESS), a space telescope designed to discover and study exoplanets. When combined with the earlier Kepler data, the data provided a 13-year baseline of observations.

“They showed that the clock had changed—the transits were happening measurably earlier than they were predicted to occur,” Vissapragada said. Kepler-1658b’s orbital period was decreasing by 131 milliseconds per year (plus or minus about 20 milliseconds), suggesting the planet will spiral into the star in about 2.5 million years.

The shrinking orbit is probably the result of tidal effects. “We think we know the total energy in the system,” Chontos said. “The planet is depositing energy in the star, causing it to rotate faster and the planet’s orbit to shrink.” A small amount of the system’s total energy could be dissipated in the planet as well, explaining some minor oddities in its orbit, Vissapragada added.

Ruling Out the Alternatives

An inspiral isn’t the only possible explanation for the apparent change in orbital period, however. The timing could appear to change if the system were moving toward us, for example. By measuring the system’s radial velocity—its motion toward or away from us—the team ruled out that possibility. It also ruled out the possibility that we see only part of the orbit’s precession period—a “wobble” in the orbit. “We think we’ve ruled out all other probable causes,” said Vissapragada.

“The evidence for inspiraling planets is plausible, and this paper presents good arguments for this being the case for this planet,” said Girish Duvvuri, a graduate research assistant at the University of Colorado Boulder who has studied the demise of exoplanets but was not involved in this project. “While I can’t say they’ve exhausted all alternative hypotheses, they covered everything I can think of.”

Even so, no one can say the fate of Kepler-1658b is sealed. The process of orbital evolution for planets around evolving stars is poorly understood, so several outcomes are possible.

“The whole dissipation process is very complicated,” Chontos said. “It involves the obliquity, eccentricity, distance—all these different aspects of the orbit that can change over time. While it’s going inward now, there’s nothing to say that the orbit won’t circularize and its migration will stop—just halt. At some point, the planet might even migrate outward. But right now, that’s all just speculation.”

The astronomers hope to narrow down the possibilities with additional observations of the system by TESS and other ground- and space-based telescopes. And they said that finding similar systems will help as well.

“We need to look at more of these systems to pin down exactly how that evolution works,” Vissapragada said. “TESS should give us a lot more examples over the next decade, so we’ll have a fairly large sample to see if this mechanism is common.”

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2023), “Hot Jupiter” is in a possible death spiral, Eos, 104, https://doi.org/10.1029/2023EO230028. Published on 31 January 2023.

Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Solar Encounter of the High-Tech Kind

It may not roll, but the surface of the Sun shakes and rattles like—pick your favorite analogy—a giant bell, a pipe organ with millions of pipes, or a concert hall filled with the hum of many orchestras tuning at the same time.

Scientists who study the Sun have used those comparisons and others to describe the star’s constant vibrations, caused primarily by sound waves rippling below the surface. Created by the motions of giant bubbles of hot gas, the waves can travel around the entire Sun, moving from the surface to deep inside to the surface again in a cycle that can repeat for anywhere from hours to months.

For solar physicists and others, the waves are powerful tools for studying the Sun, other stars, and even other fields of physics. They have probed the Sun’s interior structure and motions, provided insights into the solar dynamo, and raised questions about the Sun’s chemical composition. They offer a glimpse of the farside of the Sun, improving space weather forecasts. And they helped solve a problem in particle physics that led to a Nobel Prize.

The study of these waves is known as helioseismology, and it uses instruments on the ground and in space to keep a constant eye on the Sun. This effort has provided 3 decades of nonstop observations that have greatly advanced our knowledge of the Sun. “Helioseismology is the only way to see inside the Sun,” said Sushanta Tripathy, an associate scientist at the National Solar Observatory (NSO) in Boulder, Colo.

“All of our observations of the Sun are based on what we can see at the surface,” said Lisa Upton, a research scientist at the Southwest Research Institute, also in Boulder. “We can’t dive in to see inside. But helioseismology is a revolutionary technique. It’s amazing, the things it can do.”

Sound Waves “All Over the Place”

Helioseismology began in the 1960s when Robert Leighton and his colleagues discovered oscillations on the surface of the Sun. “He was looking at solar granulation, and turbulence was a big topic at the time,” said John Leibacher, an emeritus astronomer at NSO and a former director. “He was taking images at a specific wavelength, and he expected, as the images got farther apart in time, they’d look less and less coherent. What he found, much to his great surprise, was that after about 5 minutes, they were back in phase.… He discovered a periodicity on the surface of the Sun, which was completely unexpected.”

A few years later, Leibacher, who studied the phenomenon for his master’s thesis, and others independently devised an explanation: sound waves trapped in a cavity just below the surface, generated by the motions of blobs of hot gas at the top of the Sun’s convection zone.

The Sun consists of three main layers. The core, which accounts for roughly 25% of the Sun’s radius, is where hydrogen nuclei fuse to make helium, converting some of their mass to energy. The core is wrapped by a radiative zone making up more than half of the Sun’s radius, where energy slowly trickles outward. The outer 25% of the solar radius consists of the convection zone, where cells of plasma as big as Texas rise like bubbles in a pot of boiling water. As the cells approach the surface, they cool, lose buoyancy, and sink. That constant churning creates pressure waves (also called sound or acoustic waves) within a few hundred kilometers of the surface.

“As the plasma rises and falls, it creates turbulence,” said Jason Jackiewicz, a professor of astronomy at New Mexico State University in Las Cruces. “That’s a source of acoustic noise. It creates sound waves all over the place, all the time. Some of them interfere constructively, building up a resonance. They’re created at the surface, then go down and back up, down and back up, down and back up. Each oscillation has certain properties, just like the waves in a musical instrument.”

“The region where the waves are created is very noisy,” said Leibacher. “Not to be too anthropomorphic, but it’s like a lot of people screaming and shouting there. Or a better analogy might be a bunch of people sitting on a piano at once. If you listen to it, it’s just white noise. It’s only because the waves last a long time that we can isolate them into individual modes.”

The waves have a roughly 5-minute period. Astronomers have discovered about 10 million individual modes for the waves, with roughly a million of them shaking and rattling the surface at any given time.

Like the seismic waves that travel through Earth as a result of earthquakes, the Sun’s waves have important diagnostic abilities. As they travel into the Sun, they’re refracted toward the surface by changes in temperature, density, and composition. Individual waves are redirected differently depending on the circumstances of their creation and their path through the Sun. A careful analysis thus provides a detailed look at conditions deep in the Sun. Some modes are better tuned to provide details about sunspots and other surface phenomena.

Astronomers “see” the waves by measuring the Doppler shift all across the Sun’s surface. Each wave causes the surface to jiggle up and down a little. The change isn’t dramatic—only a few meters to a few tens of meters per second. To put that in perspective, Usain Bolt runs the 100-meter dash at about 10 meters per second.

Detecting and understanding the waves require long-term monitoring of the Sun. That can’t be accomplished by a single ground-based station, so astronomers have built networks of Sun-watching telescopes across the planet. They’ve also placed instruments in space, where they can stare at the Sun constantly, unobstructed by clouds or the blurring effects of Earth’s atmosphere.

One early helioseismology network was GONG (Global Oscillation Network Group), established by NSO in 1995. Still in operation today, it consists of six small, identical stations around the world, one each in California, Hawaii, the Canary Islands, Australia, Chile, and India. “We joke that the Sun never sets on GONG,” said Leibacher.

Each station, housed in an industrial cargo container, includes an interferometer to measure the Sun’s surface oscillations and an instrument to measure it’s magnetic field, allowing scientists to correlate the surface waves with magnetic activity.

The first space-based helioseismology instrument took to the skies shortly after GONG entered service, aboard SOHO (Solar and Heliospheric Observatory). Although SOHO continues to operate, the instrument was retired in 2011 when it was superseded by the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). HMI provides higher resolution and a higher data rate than its predecessor.

“When ground-based telescopes look at the Sun, they see it through this boiling cauldron of atmosphere,” said SDO project scientist W. Dean Pesnell at NASA’s Goddard Space Flight Center in Maryland. “That introduces a lot of noise. We don’t have that problem.”

Small Particles, Big Science

Early discoveries with helioseismology applied as much to general questions in physics as to the Sun itself, beginning with the “solar neutrino problem.”

Neutrinos are created in abundance during nuclear fusion reactions in the cores of the Sun and other stars. Because neutrinos are almost massless, they zip through the Sun and Earth without interfering with other particles. That makes them good probes of what’s happening in the Sun’s core, but it also makes them difficult to catch.

Early detectors counted only a third as many neutrinos as expected from models of the solar interior. “The nuclear physicists all said, ‘Oh, our theories are right, and your observations must be wrong—the temperature of the Sun must be a little cooler than you astronomers think,’” said Leibacher. “We said, ‘No, there’s nothing wrong with our observations; there must be something wrong with the physics of neutrinos.’ For once, we were right.”

Helioseismology confirmed that the Sun’s interior temperature profile was as expected, leaving nuclear physicists to ponder other solutions. They eventually realized that the neutrinos produced by the Sun were transforming themselves into one of two other “flavors” as they raced through the solar system. The physicists who discovered the solution received the 2015 Nobel Prize in Physics.

Tachocline and Core

In addition to confirming the Sun’s internal temperatures, early observations also confirmed its interior structure, with a sharp, well-defined boundary at the base of the convection zone that can be pinpointed to within less than 1% of the Sun’s radius.

“There are lovely results on…the existence of the tachocline—a shear layer that marks the transition between the convection zone, which has differential rotation, and the radiative region, which rotates uniformly as far as we can tell,” said Yvonne Elsworth, a professor of helioseismology, physics, and astronomy at the University of Birmingham in the United Kingdom. Elsworth is a former director of the first helioseismology network, BiSON (Birmingham Solar Oscillations Network), which has been watching the Sun since 1976.

Details about the energy-generating core, however, have proven harder to obtain. “The acoustic waves don’t spend very much time there to sense the rotation, and not many of them [go that deep], so they’re hard to observe,” said Jack Harvey, an emeritus astronomer at NSO and one of the creators of GONG. “Our knowledge of the core is very fragmentary.”

Another type of wave, known as a gravity wave, could help test those models. These longer-frequency waves are generated by oscillations in the core itself. They produce little or no signal at the surface, making them difficult to detect.

A 2017 study reported seeing the imprint of gravity waves in 16.5 years of data from SOHO, suggesting that the core rotates roughly once per week, compared with roughly once every 4 weeks at the surface (bit.ly/gravity-sun-core). However not all solar physicists accept these results. “We don’t really know if [gravity waves] have been observed yet,” said Harvey.

Cycling Through the Sunspots

Although helioseismology has not yet answered questions about the core, it’s provided many details about the convection zone, in particular its rotation.

Astronomers have known for centuries that the surface of the Sun rotates differentially. By tracking sunspots as they crossed the solar disk, they could see that the polar regions rotate faster than the equator. Helioseismology confirmed that the differential rotation continues through the convection zone all the way to the shear layer.

“Identifying that shear layer is important because solar activity is caused by magnetic fields, and there was a big question about where the magnetic field is generated,” said Alexei Pevtsov, associate director of the NSO Integrated Synoptic Program. “That strong shear layer, at the base of the convection zone, is where the dynamo operates.”

Yet the dynamo is poorly understood, leaving scientists to ponder how it helps drive the Sun’s magnetic cycle.

The cycle lasts roughly 11 years. At its peak, many dark sunspots speckle the Sun’s surface. The peak also produces a greater number of solar flares and eruptions of giant clouds of hot gas known as coronal mass ejections. At the cycle’s low point, the surface is almost bereft of such activity. At the end of a cycle the Sun’s polarity flips, with the north magnetic pole becoming the south magnetic pole and vice versa, making the overall cycle 22 years long.

No two cycles are the same. “The cycle is regular, but it’s not perfectly regular,” said Sarah Gibson, a senior scientist at the National Center for Atmospheric Research’s High Altitude Observatory in Boulder. Cycles vary in both length and intensity. The most recently completed one, which ended in December 2019, was one of the weakest on record. The current cycle was forecast to be equally meager, and it began that way, but it has exceeded projections in recent months.

One key to the solar cycle is a “conveyor-belt” flow revealed by helioseismology. Known as a meridional flow, it resembles the Hadley cells in Earth’s atmosphere. The basic concept says giant cells of plasma move from the equator toward the poles. There, they dive below the surface, then flow back toward the equator, where they return to the surface, completing the cycle.

The flow is “very important to theories of solar activity,” said Harvey. “Our best theories of the solar cycle depend on that kind of flow, so we’d like to know what it’s like. But the measurements are very subtle because the flows move at a few meters per second. You can run that fast.”

The measurements are further complicated by the fact that neither ground-based nor current space-based telescopes can see the poles.

“A polar view is the linchpin in all of this,” said Gibson, who served as project scientist for SOLARIS, a proposed solar polar mission that was rejected by NASA earlier this year. “If we can observe the poles, see the flows, we could rule out some mechanisms.”

Improving Weather Forecasts

Understanding the Sun’s magnetic cycle better is important for a practical application: forecasting space weather. As heavy outbursts of solar radiation and charged particles interact with Earth’s own magnetic field, they can damage orbiting satellites, knock out power grids on Earth’s surface, weaken oil pipelines, and cause other problems. NOAA, the U.S. Air Force, and several international organizations provide space weather forecasts to help operators protect potentially vulnerable assets.

Helioseismology is providing rough views of the Sun’s farside, offering warnings of large sunspots days before they rotate into view. “This is one of the big achievements of the whole field of helioseismology,” said Tripathy.

As waves travel through the Sun, they interact differently with sunspots than with the unblemished surface. And because the waves can travel around the entire star, some of them reveal the presence of farside sunspots as the waves ripple to the nearside. “We can predict that an active region that we’ve never actually seen before will appear on the east limb of the Sun on this date and at this location,” said Leibacher. “It’s an interesting party trick, if you will. It’s also interesting solar physics.”

As the databases of observations grow larger, scientists are testing other interesting bits of solar physics as well. As one example, the observations aren’t necessarily agreeing with profiles of the Sun’s composition obtained through other techniques.

The Sun consists almost entirely of hydrogen and helium, with a smattering of heavier elements—about 2% of its total mass—that were forged inside other stars. The heavier elements, known as metals, were expelled into space when the stars died and were then incorporated into the Sun as it formed from a cloud of interstellar gas and dust. Slight variations in the proportions of these elements cause differences in a star’s internal temperatures and other characteristics, so fully understanding what’s going on inside a star today—and how the star will evolve—requires precise knowledge of its composition.

It seems like there are fewer metals in the Sun than researchers thought, said Jackiewicz. “That has major implications for stellar astrophysics in general. We compare every star to the Sun—‘That star has 10% of the metallicity of the Sun, or that star has twice the metallicity.’ That’s great, but it assumes we know the metallicity of the Sun. I don’t know that anyone’s willing to say we know that for sure anymore.”

From One Star to Many

Although astronomers use helioseismology in part to learn about how other stars operate, they use a similar technique—asteroseismology—to study other stars in part to learn about the Sun.

Asteroseismology observations have come from the databases of Kepler, TESS (Transiting Exoplanet Survey Satellite), and other satellites designed to hunt for exoplanets. The craft keep a steady gaze on large numbers of star systems for weeks or longer, so their observations can be used to glean information about the stars as well as their planets.

Because the stars are so far away, they appear as just pinpoints of light, so astronomers can’t detect the shaking and rattling with the same level of detail as on the Sun. Instead of millions of different modes, they see perhaps a few dozen, observed as minor changes in brightness rather than changes in surface motion, which are integrated across the star’s entire disk. Still, that provides enough information to characterize a star’s interior temperature and structure.

“We’ve measured the pulsations of about 30,000 stars,” said Jackiewicz. The vast majority are red giants—old, bloated stars that have converted the hydrogen in their cores to helium and now are beginning to fuse the helium to produce heavier elements. “That’s the boon of the last 10 years of asteroseismology, which is great, because the Sun will become a red giant in a few billion years.”

A red giant’s core is smaller, denser, and hotter than the Sun’s, so it produces stronger gravity waves, which are more easily detected at the star’s surface. “So we know more about the rotation of the cores of red giants than the Sun,” Jackiewicz said.

With asteroseismology, “we can look at 10,000 different realizations of the Sun,” said Leibacher. “We can observe the Sun only today, not in a million or a billion or 5 billion years. But we…can do asteroseismology of what the Sun will become, which is pretty amazing.”

Asteroseismology is also helping astronomers study exoplanets. “The properties of the stars are tied to the properties of the planets,” said Jackiewicz. “With seismology, we have access to parameters and things that traditional observations don’t. So we can tell if it’s a Jupiter-type planet or an Earth-type planet. It’s a really active area of research.”

Helioseismology remains an active area as well, although its tools are aging. SDO, for example, has been operating for more than 12 years. Although it’s in good shape and could go for several more years if it receives funding, according to Pesnell, its instruments can’t be upgraded, and the spacecraft can’t be serviced if something goes wrong.

And GONG “is getting a little long in the tooth,” according to both Harvey and Leibacher. “It was designed for 3 years, not 30,” said Harvey.

GONG scientists have proposed a next-generation version of the network that would incorporate improved instruments, better enclosures than the current cargo containers, and perhaps sites at higher altitudes to enable observations of the Sun’s hot outer atmosphere, the corona. Last year, however, the National Science Foundation rejected a proposal for the new network.

“We’ve refurbished GONG’s cameras and computers, so we can probably extend it for another 5, 7, maybe 10 years, but not more than that,” said Pevtsov. “It won’t last forever.”

“I think a next-generation GONG is more or less inevitable; it’s only a matter of how and when,” said Leibacher. “But we can’t just skip a [solar] cycle. You can’t rewind and see what happened 10 years ago. You have to be observing day by day to try to make sense of the Sun’s dynamo”—and understand how the surface keeps shaking and rattling with a million vibrations.

Author Information

Damond Benningfield (damond@damondbenningfield.com), Science Writer

Citation: Benningfield, D. (2022), Shake, rattle, and probe, Eos, 103, https://doi.org/10.1029/2022EO220410. Published on 25 August 2022.

Text © 2022. The authors. CC BY-NC-ND 3.0
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Source: Journal of Geophysical Research: Planets

The ice giants, Uranus and Neptune, are the least understood planets in the solar system. They remain the only worlds that an orbital spacecraft has not visited. Our limited understanding of them derives largely from the flyby of NASA’s Voyager 2 probe and subsequent observations with the Hubble Space Telescope. Yet the ice giants may be most representative of the extrasolar planets in our local vicinity.

Why these planets appear so different in color despite having very similar physical properties, including vertical temperature profile and atmospheric composition, is a mystery. Past investigations have attributed Neptune’s deeper blue largely to excess absorption in the red and near infrared from atmospheric methane. But the two planets have always been treated independently despite their similarities. Without a comprehensive atmospheric model, direct comparisons between the worlds remain difficult.

Irwin et al. attempt to fill this gap by developing a single atmospheric model consistent with the spectral observations of both planets. They fit near-infrared spectra collected by Hubble, as well as the ground-based Gemini and NASA Infrared Telescope Facility (IRTF) telescopes, to a three-layer aerosol model.

The topmost layer of this structure consists of haze resulting from photochemistry involving unknown atmospheric constituents. This haze is then somehow concentrated into a stable layer spanning from 1 bar down to approximately 2 bars. This main haze layer is roughly twice as thick on Uranus as it is on Neptune, giving Uranus a distinctly paler blue color.

In addition, at the base of the intermediate layer, the haze particles serve as condensation nuclei for atmospheric methane. These now heavy methane ice particles snow downward to a depth of 5–7 bars, where they heat up enough for the methane to evaporate. In this deepest layer, surviving haze particles become nucleation sites for another round of condensation, this time involving hydrogen sulfide.

This combined model mirrors the significant similarities that appear to exist between the ice giant planets. Yet much of the mechanism and its constituent molecules remains unknown. This issue is likely to persist until the arrival of a Uranus orbiter, the development of which has been identified as a primary goal in the most recent planetary science decadal survey. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2022JE007189, 2022)

—Morgan Rehnberg, Science Writer

Citation: Rehnberg, M. (2022), A unified atmospheric model for Uranus and Neptune, Eos, 103, https://doi.org/10.1029/2022EO220369. Published on 1 August 2022.

Text © 2022. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

While people were isolating in their homes at the start of the COVID-19 pandemic, Allen Foster was in the “only place on Earth that didn’t have COVID”: the Amundsen-Scott South Pole Station in Antarctica. He was there working on the South Pole Telescope (SPT). “It was kind of a surreal thing,” said Foster, a Ph.D. candidate at Case Western Reserve University in Cleveland.

During his 10-month South Pole assignment in 2019, Foster focused on determining how well the SPT could sort light from some of the most extreme phenomena in the universe: the cosmic microwave background and black holes.

Foster has the unique and rare experience of being one of only around a thousand people each year who overwinter in Antarctica. Not only do temperatures fall to nearly –80°C (–110°F), but also darkness covers the land throughout the entire 7-month season (February through August), making many scientists steer clear of such a tough work environment.

Although some polar scientists can suffer from winter-over syndrome, “I love being in Antarctica,” said Foster. During the long, dark winter, he enjoys seeing “all the dust splotches in the galaxy and the superbright, super colorful auroras.” He has gotten used to the continent’s extreme temperatures and regularly records his thoughts and experiences in his blog.

In 2022, Foster found himself back at the South Pole as a telescope operator, about a year after his first stint at the station. He now is responsible for scheduling observations using the SPT as well as installing and maintaining the equipment, which includes “lots of greasing.” He also helps train new SPT crew.

The SPT keeps Foster busy. The telescope is part of the global Event Horizon Telescope array, which aims to image objects the size of a supermassive black hole’s event horizon. In March 2022, the Event Horizon Telescope’s 2-week observation window to search for black holes, galaxies, and quasars meant 16-hour workdays for Foster. These stretches weren’t actually work days, he said. “[They] happened to be overnight for us because we’re in a weird time zone.”

Foster is also working on his doctoral thesis using observations and data from the SPT to look for deep solar system objects like the possible Planet 9. If this planet exists, it would be so far from the Sun that it would be very difficult to observe through an optical telescope. But according to Foster, “it’s possible it has a reasonably strong thermal emission, which would be visible to the SPT-3G experiment” (the third survey receiver operating on the South Pole Telescope dedicated to high-resolution observations of the cosmic microwave background). He hopes his thesis will show the power and possibilities of the SPT for future observations of distant celestial objects at millimeter wavelengths.

This profile is part of a special series in our August 2022 issue on science careers.

—Santiago Flórez (@rflorezsantiago), Science Writer

Citation: Flórez, S. (2022), Allen Foster: Greasing telescope gears during a 7-month-long night, Eos, 103, https://doi.org/10.1029/2022EO220342. Published on 25 July 2022.

Text © 2022. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.