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Hubble observations used to answer key exoplanet questions
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This NASA/ESA Hubble Space Telescope image features a peculiar spiral galaxy called Arp 184 or NGC 1961.ESA/Hubble & NASA, J. Dalcanton, R. J. Foley (UC Santa Cruz), C. Kilpatrick A beautiful but skewed spiral galaxy dazzles in this NASA/ESA Hubble Space Telescope image. The galaxy, called Arp 184 or NGC 1961, sits about 190 million light-years away from Earth in the constellation Camelopardalis (The Giraffe).
The name Arp 184 comes from the Atlas of Peculiar Galaxies compiled by astronomer Halton Arp in 1966. It holds 338 galaxies that are oddly shaped and tend to be neither entirely elliptical nor entirely spiral-shaped. Many of the galaxies are in the process of interacting with other galaxies, while others are dwarf galaxies without well-defined structures. Arp 184 earned its spot in the catalog thanks to its single broad, star-speckled spiral arm that appears to stretch toward us. The galaxy’s far side sports a few wisps of gas and stars, but it lacks a similarly impressive spiral arm.
This Hubble image combines data from three Snapshot observing programs, which are short observations that slotted into time gaps between other proposals. One of the three programs targeted Arp 184 for its peculiar appearance. This program surveyed galaxies listed in the Atlas of Peculiar Galaxies as well as A Catalogue of Southern Peculiar Galaxies and Associations, a similar catalog compiled by Halton Arp and Barry Madore.
The remaining two Snapshot programs looked at the aftermath of fleeting astronomical events like supernovae and tidal disruption events — like when a supermassive black hole rips a star apart after it wanders too closely. Since Arp 184 hosted four known supernovae in the past three decades, it is a rich target for a supernova hunt.
Image credit: ESA/Hubble & NASA, J. Dalcanton, R. J. Foley (UC Santa Cruz), C. Kilpatrick
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Explore This Section Webb News Latest News Latest Images Webb’s Blog Awards X (offsite – login reqd) Instagram (offsite – login reqd) Facebook (offsite- login reqd) Youtube (offsite) Overview About Who is James Webb? Fact Sheet Impacts+Benefits FAQ Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning 6 Min Read NASA’s Webb Lifts Veil on Common but Mysterious Type of Exoplanet
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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Space Telescope Science Institute, Baltimore, Md.
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Space Telescope Science Institute, Baltimore, Md.
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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 Images a Peculiar Spiral
This NASA/ESA Hubble Space Telescope image features a peculiar spiral galaxy called Arp 184 or NGC 1961. ESA/Hubble & NASA, J. Dalcanton, R. J. Foley (UC Santa Cruz), C. Kilpatrick A beautiful but skewed spiral galaxy dazzles in this NASA/ESA Hubble Space Telescope image. The galaxy, called Arp 184 or NGC 1961, sits about 190 million light-years away from Earth in the constellation Camelopardalis (The Giraffe).
The name Arp 184 comes from the Atlas of Peculiar Galaxies compiled by astronomer Halton Arp in 1966. It holds 338 galaxies that are oddly shaped and tend to be neither entirely elliptical nor entirely spiral-shaped. Many of the galaxies are in the process of interacting with other galaxies, while others are dwarf galaxies without well-defined structures. Arp 184 earned its spot in the catalog thanks to its single broad, star-speckled spiral arm that appears to stretch toward us. The galaxy’s far side sports a few wisps of gas and stars, but it lacks a similarly impressive spiral arm.
This Hubble image combines data from three Snapshot observing programs, which are short observations that slotted into time gaps between other proposals. One of the three programs targeted Arp 184 for its peculiar appearance. This program surveyed galaxies listed in the Atlas of Peculiar Galaxies as well as A Catalogue of Southern Peculiar Galaxies and Associations, a similar catalog compiled by Halton Arp and Barry Madore.
The remaining two Snapshot programs looked at the aftermath of fleeting astronomical events like supernovae and tidal disruption events — like when a supermassive black hole rips a star apart after it wanders too closely. Since Arp 184 hosted four known supernovae in the past three decades, it is a rich target for a supernova hunt.
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NASA’s Goddard Space Flight Center, Greenbelt, MD
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Last Updated May 01, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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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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NASA’s Goddard Space Flight Center, Greenbelt, MD
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Last Updated Apr 25, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
An astronaut glove designed for International Space Station spacewalks is prepped for testing in a chamber called CITADEL at NASA JPL. Conducted at temperatures as frigid as those Artemis III astronauts will see on the lunar South Pole, the testing supports next-generation spacesuit development.NASA/JPL-Caltech Engineers with NASA Johnson and the NASA Engineering and Safety Center ready an astronaut glove for insertion into the main CITADEL chamber at JPL. The team tested the glove in vacuum at minus 352 degrees Fahrenheit (minus 213 degrees Celsius).NASA/JPL-Caltech A JPL facility built to support potential robotic spacecraft missions to frozen ocean worlds helps engineers develop safety tests for next-generation spacesuits.
When NASA astronauts return to the Moon under the Artemis campaign and eventually venture farther into the solar system, they will encounter conditions harsher than any humans have experienced before. Ensuring next-generation spacesuits protect astronauts requires new varieties of tests, and a one-of-a-kind chamber called CITADEL (Cryogenic Ice Testing, Acquisition Development, and Excavation Laboratory) at NASA’s Jet Propulsion Laboratory in Southern California is helping.
Built to prepare potential robotic explorers for the frosty, low-pressure conditions on ocean worlds like Jupiter’s frozen moon Europa, CITADEL also can evaluate how spacesuit gloves and boots hold up in extraordinary cold. Spearheaded by the NASA Engineering and Safety Center, a glove testing campaign in CITADEL ran from October 2023 to March 2024. Boot testing, initiated by the Extravehicular Activity and Human Surface Mobility Program at NASA’s Johnson Space Center in Houston, took place from October 2024 to January 2025.
An astronaut boot — part of a NASA lunar spacesuit prototype, the xEMU — is readied for testing in JPL’s CITADEL. A thick aluminum plate stands in for the cold surface of the lunar South Pole, where Artemis III astronauts will confront conditions more extreme than any humans have yet experienced.NASA/JPL-Caltech In coming months, the team will adapt CITADEL to test spacesuit elbow joints to evaluate suit fabrics for longevity on the Moon. They’ll incorporate abrasion testing and introduce a simulant for lunar regolith, the loose material that makes up the Moon’s surface, into the chamber for the first time.
“We’ve built space robots at JPL that have gone across the solar system and beyond,” said Danny Green, a mechanical engineer who led the boot testing for JPL. “It’s pretty special to also use our facilities in support of returning astronauts to the Moon.”
Astronauts on the Artemis III mission will explore the Moon’s South Pole, a region of much greater extremes than the equatorial landing sites visited by Apollo-era missions. They’ll spend up to two hours at a time inside craters that may contain ice deposits potentially important to sustaining long-term human presence on the Moon. Called permanently shadowed regions, these intriguing features rank among the coldest locations in the solar system, reaching as low as minus 414 degrees Fahrenheit (minus 248 degrees Celsius). The CITADEL chamber gets close to those temperatures.
Engineers from JPL and NASA Johnson set up a test of the xEMU boot inside CITADEL. Built to prepare potential robotic explorers for conditions on ocean worlds like Jupiter’s moon Europa, the chamber offers unique capabilities that have made it useful for testing spacesuit parts.NASA/JPL-Caltech “We want to understand what the risk is to astronauts going into permanently shadowed regions, and gloves and boots are key because they make prolonged contact with cold surfaces and tools,” said Zach Fester, an engineer with the Advanced Suit Team at NASA Johnson and the technical lead for the boot testing.
Keeping Cool
Housed in the same building as JPL’s historic 10-Foot Space Simulator, the CITADEL chamber uses compressed helium to get as low as minus 370 F (minus 223 C) — lower than most cryogenic facilities, which largely rely on liquid nitrogen. At 4 feet (1.2 meters) tall and 5 feet (1.5 meters) in diameter, the chamber is big enough for a person to climb inside.
An engineer collects simulated lunar samples while wearing the Axiom Extravehicular Mobility Unit spacesuit during testing at NASA Johnson in late 2023. Recent testing of existing NASA spacesuit designs in JPL’s CITADEL chamber will ultimately support de-velopment of next-generation suits being built by Axiom Space.Axiom Space More important, it features four load locks, drawer-like chambers through which test materials are inserted into the main chamber while maintaining a chilled vacuum state. The chamber can take several days to reach test conditions, and opening it to insert new test materials starts the process all over again. The load locks allowed engineers to make quick adjustments during boot and glove tests.
Cryocoolers chill the chamber, and aluminum blocks inside can simulate tools astronauts might grab or the cold lunar surface on which they’d walk. The chamber also features a robotic arm to interact with test materials, plus multiple visible-light and infrared cameras to record operations.
Testing Extremities
The gloves tested in the chamber are the sixth version of a glove NASA began using in the 1980s, part of a spacesuit design called the Extravehicular Mobility Unit. Optimized for spacewalks at the International Space Station, the suit is so intricate it’s essentially a personal spacecraft. Testing in CITADEL at minus 352 F (minus 213 C) showed the legacy glove would not meet thermal requirements in the more challenging environment of the lunar South Pole. Results haven’t yet been fully analyzed from boot testing, which used a lunar surface suit prototype called the Exploration Extravehicular Mobility Unit. NASA’s reference design of an advanced suit architecture, this spacesuit features enhanced fit, mobility, and safety.
In addition to spotting vulnerabilities with existing suits, the CITADEL experiments will help NASA prepare criteria for standardized, repeatable, and inexpensive test methods for the next-generation lunar suit being built by Axiom Space — the Axiom Extravehicular Mobility Unit, which NASA astronauts will wear during the Artemis III mission.
“This test is looking to identify what the limits are: How long can that glove or boot be in that lunar environment?” said Shane McFarland, technology development lead for the Advanced Suit Team at NASA Johnson. “We want to quantify what our capability gap is for the current hardware so we can give that information to the Artemis suit vendor, and we also want to develop this unique test capability to assess future hardware designs.”
In the past, astronauts themselves have been part of thermal testing. For gloves, an astronaut inserted a gloved hand into a chilled “glove box,” grabbed a frigid object, and held it until their skin temperature dropped as low as 50 F (10 C). McFarland stressed that such human-in-the-loop testing remains essential to ensuring future spacesuit safety but doesn’t produce the consistent data the team is looking for with the CITADEL testing.
To obtain objective feedback, the CITADEL testing team used a custom-built manikin hand and foot. A system of fluid loops mimicked the flow of warm blood through the appendages, while dozens of temperature and heat flux sensors provided data from inside gloves and boots.
“By using CITADEL and modern manikin technology, we can test design iterations faster and at much lower cost than traditional human-in-the-loop testing,” said Morgan Abney, NASA technical fellow for Environmental Control and Life Support, who conceived the glove testing effort. “Now we can really push the envelope on next-generation suit designs and have confidence we understand the risks. We’re one step closer to landing astronauts back on the Moon.”
Through Artemis, NASA will send astronauts to explore the Moon for scientific discovery, economic benefits, and build the foundation for the first crewed missions to Mars.
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