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This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like. It is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. Credits:
Illustration: NASA, ESA, CSA, Dani Player (STScI) Though they don’t orbit around our Sun, sub-Neptunes are the most common type of exoplanet, or planet outside our solar system, that have been observed in our galaxy. These small, gassy planets are shrouded in mystery…and often, a lot of haze. Now, by observing exoplanet TOI-421 b, NASA’s James Webb Space Telescope is helping scientists understand sub-Neptunes in a way that was not possible prior to the telescope’s launch.
“I had been waiting my entire career for Webb so that we could meaningfully characterize the atmospheres of these smaller planets,” said principal investigator Eliza Kempton of the University of Maryland, College Park. “By studying their atmospheres, we’re getting a better understanding of how sub-Neptunes formed and evolved, and part of that is understanding why they don’t exist in our solar system.”
Image A: Artist’s Concept of TOI-421 b
This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like. It is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. Illustration: NASA, ESA, CSA, Dani Player (STScI) Small, Cool, Shrouded in Haze
The existence of sub-Neptunes was unexpected before they were discovered by NASA’s retired Kepler space telescope in the last decade. Now, astronomers are trying to understand where these planets came from and why are they so common.
Before Webb, scientists had very little information on them. While sub-Neptunes are a few times larger than Earth, they are still much smaller than gas-giant planets and typically cooler than hot Jupiters, making them much more challenging to observe than their gas-giant counterparts.
A key finding prior to Webb was that most sub-Neptune atmospheres had flat or featureless transmission spectra. This means that when scientists observed the spectrum of the planet as it passed in front of its host star, instead of seeing spectral features – the chemical fingerprints that would reveal the composition of the atmosphere – they saw only a flat-line spectrum. Astronomers concluded from all of those flat-line spectra that at least certain sub-Neptunes were probably very highly obscured by either clouds or hazes.
Image B: Spectrum of TOI-421 b
A transmission spectrum captured by NASA’s James Webb Space Telescope reveals chemicals in the atmosphere of the hot sub-Neptune exoplanet TOI-421 b. Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI) A Different Kind of Sub-Neptune?
“Why did we observe this planet, TOI-421 b? It’s because we thought that maybe it wouldn’t have hazes,” said Kempton. “And the reason is that there were some previous data that implied that maybe planets over a certain temperature range were less enshrouded by haze or clouds than others.”
That temperature threshold is about 1,070 degrees Fahrenheit. Below that, scientists hypothesized that a complex set of photochemical reactions would occur between sunlight and methane gas, and that would trigger the haze. But hotter planets shouldn’t have methane and therefore perhaps shouldn’t have haze.
The temperature of TOI-421 b is about 1,340 degrees Fahrenheit, well above the presumed threshold. Without haze or clouds, researchers expected to see a clear atmosphere – and they did!
A Surprising Finding
“We saw spectral features that we attribute to various gases, and that allowed us to determine the composition of the atmosphere,” said the University of Maryland’s Brian Davenport, a third-year Ph.D. student who conducted the primary data analysis. “Whereas with many of the other sub-Neptunes that had been previously observed, we know their atmospheres are made of something, but they’re being blocked by haze.”
The team found water vapor in the planet’s atmosphere, as well as tentative signatures of carbon monoxide and sulfur dioxide. Then there are molecules they didn’t detect, such as methane and carbon dioxide. From the data, they can also infer that a large amount of hydrogen is in TOI-421 b’s atmosphere.
The lightweight hydrogen atmosphere was the big surprise to the researchers. “We had recently wrapped our mind around the idea that those first few sub-Neptunes observed by Webb had heavy-molecule atmospheres, so that had become our expectation, and then we found the opposite,” said Kempton. This suggests TOI-421 b may have formed and evolved differently from the cooler sub-Neptunes observed previously.
Is TOI-421 b Unique?
The hydrogen-dominated atmosphere is also interesting because it mimics the composition of TOI-421 b’s host star. “If you just took the same gas that made the host star, plopped it on top of a planet’s atmosphere, and put it at the much cooler temperature of this planet, you would get the same combination of gases. That process is more in line with the giant planets in our solar system, and it is different from other sub-Neptunes that have been observed with Webb so far,” said Kempton.
Aside from being hotter than other sub-Neptunes previously observed with Webb, TOI-421 b orbits a Sun-like star. Most of the other sub-Neptunes that have been observed so far orbit smaller, cooler stars called red dwarfs.
Is TOI-421b emblematic of hot sub-Neptunes orbiting Sun-like stars, or is it just that exoplanets are very diverse? To find out, the researchers would like to observe more hot sub-Neptunes to determine if this is a unique case or a broader trend. They hope to gain insights into the formation and evolution of these common exoplanets.
“We’ve unlocked a new way to look at these sub-Neptunes,” said Davenport. “These high-temperature planets are amenable to characterization. So by looking at sub-Neptunes of this temperature, we’re perhaps more likely to accelerate our ability to learn about these planets.”
The team’s findings appear on May 5 in the Astrophysical Journal Letters.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
To learn more about Webb, visit:
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
JunoCam, the visible light imager aboard NASA’s Juno, captured this enhanced-color view of Ju-piter’s northern high latitudes from an altitude of about 36,000 miles (58,000 kilometers) above the giant planet’s cloud tops during the spacecraft’s 69th flyby on Jan. 28, 2025. Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing: Jackie Branc (CC BY) New data from the agency’s Jovian orbiter sheds light on the fierce winds and cyclones of the gas giant’s northern reaches and volcanic action on its fiery moon.
NASA’s Juno mission has gathered new findings after peering below Jupiter’s cloud-covered atmosphere and the surface of its fiery moon, Io. Not only has the data helped develop a new model to better understand the fast-moving jet stream that encircles Jupiter’s cyclone-festooned north pole, it’s also revealed for the first time the subsurface temperature profile of Io, providing insights into the moon’s inner structure and volcanic activity.
Team members presented the findings during a news briefing in Vienna on Tuesday, April 29, at the European Geosciences Union General Assembly.
“Everything about Jupiter is extreme. The planet is home to gigantic polar cyclones bigger than Australia, fierce jet streams, the most volcanic body in our solar system, the most powerful aurora, and the harshest radiation belts,” said Scott Bolton, principal investigator of Juno at the Southwest Research Institute in San Antonio. “As Juno’s orbit takes us to new regions of Jupiter’s complex system, we’re getting a closer look at the immensity of energy this gas giant wields.”
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Made with data from the JIRAM instrument aboard NASA’s Juno, this animation shows the south polar region of Jupiter’s moon Io during a Dec. 27, 2024, flyby. The bright spots are locations with higher temperatures caused by volcanic activity; the gray areas resulted when Io left the field of view.NASA/JPL/SwRI/ASI – JIRAM Team (A.M.) Lunar Radiator
While Juno’s microwave radiometer (MWR) was designed to peer beneath Jupiter’s cloud tops, the team has also trained the instrument on Io, combining its data with Jovian Infrared Auroral Mapper (JIRAM) data for deeper insights.
“The Juno science team loves to combine very different datasets from very different instruments and see what we can learn,” said Shannon Brown, a Juno scientist at NASA’s Jet Propulsion Laboratory in Southern California. “When we incorporated the MWR data with JIRAM’s infrared imagery, we were surprised by what we saw: evidence of still-warm magma that hasn’t yet solidified below Io’s cooled crust. At every latitude and longitude, there were cooling lava flows.”
The data suggests that about 10% of the moon’s surface has these remnants of slowly cooling lava just below the surface. The result may help provide insight into how the moon renews its surface so quickly as well as how as well as how heat moves from its deep interior to the surface.
“Io’s volcanos, lava fields, and subterranean lava flows act like a car radiator,” said Brown, “efficiently moving heat from the interior to the surface, cooling itself down in the vacuum of space.”
Looking at JIRAM data alone, the team also determined that the most energetic eruption in Io’s history (first identified by the infrared imager during Juno’s Dec. 27, 2024, Io flyby) was still spewing lava and ash as recently as March 2. Juno mission scientists believe it remains active today and expect more observations on May 6, when the solar-powered spacecraft flies by the fiery moon at a distance of about 55,300 miles (89,000 kilometers).
This composite image, derived from data collected in 2017 by the JIRAM instrument aboard NASA’s Juno, shows the central cyclone at Jupiter’s north pole and the eight cy-clones that encircle it. Data from the mission indicates these storms are enduring fea-tures.NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM Colder Climes
On its 53rd orbit (Feb 18, 2023), Juno began radio occultation experiments to explore the gas giant’s atmospheric temperature structure. With this technique, a radio signal is transmitted from Earth to Juno and back, passing through Jupiter’s atmosphere on both legs of the journey. As the planet’s atmospheric layers bend the radio waves, scientists can precisely measure the effects of this refraction to derive detailed information about the temperature and density of the atmosphere.
So far, Juno has completed 26 radio occultation soundings. Among the most compelling discoveries: the first-ever temperature measurement of Jupiter’s north polar stratospheric cap reveals the region is about 11 degrees Celsius cooler than its surroundings and is encircled by winds exceeding 100 mph (161 kph).
Polar Cyclones
The team’s recent findings also focus on the cyclones that haunt Jupiter’s north. Years of data from the JunoCam visible light imager and JIRAM have allowed Juno scientists to observe the long-term movement of Jupiter’s massive northern polar cyclone and the eight cyclones that encircle it. Unlike hurricanes on Earth, which typically occur in isolation and at lower latitudes, Jupiter’s are confined to the polar region.
By tracking the cyclones’ movements across multiple orbits, the scientists observed that each storm gradually drifts toward the pole due to a process called “beta drift” (the interaction between the Coriolis force and the cyclone’s circular wind pattern). This is similar to how hurricanes on our planet migrate, but Earthly cyclones break up before reaching the pole due to the lack of warm, moist air needed to fuel them, as well as the weakening of the Coriolis force near the poles. What’s more, Jupiter’s cyclones cluster together while approaching the pole, and their motion slows as they begin interacting with neighboring cyclones.
“These competing forces result in the cyclones ‘bouncing’ off one another in a manner reminiscent of springs in a mechanical system,” said Yohai Kaspi, a Juno co-investigator from the Weizmann Institute of Science in Israel. “This interaction not only stabilizes the entire configuration, but also causes the cyclones to oscillate around their central positions, as they slowly drift westward, clockwise, around the pole.”
The new atmospheric model helps explain the motion of cyclones not only on Jupiter, but potentially on other planets, including Earth.
“One of the great things about Juno is its orbit is ever-changing, which means we get a new vantage point each time as we perform a science flyby,” said Bolton. “In the extended mission, that means we’re continuing to go where no spacecraft has gone before, including spending more time in the strongest planetary radiation belts in the solar system. It’s a little scary, but we’ve built Juno like a tank and are learning more about this intense environment each time we go through it.”
More About Juno
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft. Various other institutions around the U.S. provided several of the other scientific instruments on Juno.
More information about Juno is at: https://www.nasa.gov/juno
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Last Updated Apr 29, 2025 Related Terms
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Explore This Section Perseverance Home Mission Overview Rover Components Mars Rock Samples Where is Perseverance? Ingenuity Mars Helicopter Mission Updates Science Overview Objectives Instruments Highlights Exploration Goals News and Features Multimedia Perseverance Raw Images Images Videos Audio More Resources Mars Missions Mars Sample Return Mars Perseverance Rover Mars Curiosity Rover MAVEN Mars Reconnaissance Orbiter Mars Odyssey More Mars Missions Mars Home 2 min read
Searching for the Dark in the Light
The Perseverance rover acquired this image of the “Hare Bay” abrasion patch using its SHERLOC WATSON camera (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals, and the Wide Angle Topographic Sensor for Operations and eNgineering), located on the turret at the end of the rover’s robotic arm. This image was acquired on April 18, 2025 (Sol 1479, or Martian day 1,479 of the Mars 2020 mission) at the local mean solar time of 12:53:57. NASA/JPL-Caltech Written by Eleanor Moreland, Ph.D. Student Collaborator at Rice University
Perseverance has been busy exploring lower “Witch Hazel Hill,” an outcrop exposed on the edge of the Jezero crater rim. The outcrop is composed of alternating light and dark layers, and naturally, the team has been trying to understand the makeup of and relationships between the light and dark layers. A few weeks ago, we sampled one of the light-toned layers, which we discovered was made up of very small clasts, or fragments of rocks or minerals, at “Main River.” Since then, we have learned that the dark layers tend to be composed of larger clasts compared to the light layers, and we’ve been searching for a place to sample this coarser-grained rock type. Sometimes, these coarser-grained rocks also contain spherules, which are of great interest to the science team because they provide clues about the process that formed these layered rocks.
Perseverance first looked at a dark layer at “Puncheon Rock” with an abrasion. We then examined a dark layer at “Wreck Apple,” near “Sally’s Cove,” but we could not identify a suitable surface to abrade. So, while team members searched for other locations to study the coarse-grained units and spherules, Perseverance drove south to “Port Anson.”
Perseverance acquired this image of the “Strong Island” workspace near Port Anson using its onboard Front Left Hazard Avoidance Camera A (https://science.nasa.gov/mission/mars-2020-perseverance/rover-components/#eyes). This image was acquired on April 12, 2025 (Sol 1473, or Martian day 1,473 of the Mars 2020 mission) at the local mean solar time of 12:50:32. NASA/JPL-Caltech Port Anson was intriguing because, from orbit, it showed a clear contact between the light layers of Witch Hazel Hill and a distinct unit below it. And, although the rocks below the Port Anson contact do show interesting compositional differences with those of Witch Hazel Hill, they weren’t the coarse-grained rocks we were looking for. We still performed an abrasion there, at Strong Island, before driving back up north for another attempt at investigating the coarser-grained rocks.
We aimed for “Pine Pond,” which neighbors “Dennis Pond,” to abrade at “Hare Bay.” With the data just coming down over the weekend, the team will be hard at work to figure out if we captured the coarse grains and spherules, and if it is representative of rocks we have seen before or not. The image below is a close-up of this most recent abrasion patch at Hare Bay — what do you think? Stay tuned to find out!
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This NASA/ESA Hubble Space Telescope image features the globular cluster Messier 72 (M72).ESA/Hubble & NASA, A. Sarajedini, G. Piotto, M. Libralato As part of ESA/Hubble’s 35th anniversary celebrations, the European Space Agency (ESA) shared new images that revisited stunning, previously released Hubble targets with the addition of the latest Hubble data and new processing techniques.
ESA/Hubble released new images of NGC 346, the Sombrero Galaxy, and the Eagle Nebula earlier in the month. Now they are revisiting the star cluster Messier 72 (M72).
M72 is a collection of stars, formally known as a globular cluster, located in the constellation Aquarius roughly 50,000 light-years from Earth. The intense gravitational attraction between the closely packed stars gives globular clusters their regular, spherical shape. There are roughly 150 known globular clusters associated with the Milky Way galaxy.
The striking variety in the color of the stars in this image of M72, particularly compared to the original image, results from the addition of ultraviolet observations to the previous visible-light data. The colors indicate groups of different types of stars. Here, blue stars are those that were originally more massive and have reached hotter temperatures after burning through much of their hydrogen fuel; the bright red objects are lower-mass stars that have become red giants. Studying these different groups help astronomers understand how globular clusters, and the galaxies they were born in, initially formed.
Pierre Méchain, a French astronomer and colleague of Charles Messier, discovered M72 in 1780. It was the first of five star clusters that Méchain would discover while assisting Messier. They recorded the cluster as the 72nd entry in Messier’s famous collection of astronomical objects. It is also one of the most remote clusters in the catalog.
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Explore Hubble Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts e-Books Online Activities Lithographs Fact Sheets Posters Hubble on the NASA App Glossary More 35th Anniversary Online Activities 2 min read
Hubble Visits Glittering Cluster, Capturing Its Ultraviolet Light
This NASA/ESA Hubble Space Telescope image features the globular cluster Messier 72 (M72). ESA/Hubble & NASA, A. Sarajedini, G. Piotto, M. Libralato As part of ESA/Hubble’s 35th anniversary celebrations, the European Space Agency (ESA) shared new images that revisited stunning, previously released Hubble targets with the addition of the latest Hubble data and new processing techniques.
ESA/Hubble released new images of NGC 346, the Sombrero Galaxy, and the Eagle Nebula earlier in the month. Now they are revisiting the star cluster Messier 72 (M72).
M72 is a collection of stars, formally known as a globular cluster, located in the constellation Aquarius roughly 50,000 light-years from Earth. The intense gravitational attraction between the closely packed stars gives globular clusters their regular, spherical shape. There are roughly 150 known globular clusters associated with the Milky Way galaxy.
The striking variety in the color of the stars in this image of M72, particularly compared to the original image, results from the addition of ultraviolet observations to the previous visible-light data. The colors indicate groups of different types of stars. Here, blue stars are those that were originally more massive and have reached hotter temperatures after burning through much of their hydrogen fuel; the bright red objects are lower-mass stars that have become red giants. Studying these different groups help astronomers understand how globular clusters, and the galaxies they were born in, initially formed.
Pierre Méchain, a French astronomer and colleague of Charles Messier, discovered M72 in 1780. It was the first of five star clusters that Méchain would discover while assisting Messier. They recorded the cluster as the 72nd entry in Messier’s famous collection of astronomical objects. It is also one of the most remote clusters in the catalog.
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