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By European Space Agency
Image: This image shows Webb’s recent observation of the asteroid 2024 YR4 using both its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Data from NIRCam shows reflected light, while the MIRI observations show thermal light.
On 8 March 2025, the NASA/ESA/CSA James Webb Space Telescope turned its watchful eye toward asteroid 2024 YR4, which we now know poses no significant threat to Earth in 2032 and beyond.
This is the smallest object targeted by Webb to date, and one of the smallest objects to have its size directly measured.
Observations were taken to study the thermal properties of 2024 YR4, including how quickly it heats up and cools down and how hot it is at its current distance from the Sun. These measurements indicate that this asteroid does not share properties observed in larger asteroids. This is likely a combination of its fast spin and lack of fine-grained sand on its surface. Further research is needed, however this is considered consistent with a surface dominated by rocks that are roughly fist-sized or larger.
Asteroid 2024 YR4 was recently under close watch by the team at ESA's Near Earth Objects Coordination Centre, located in Italy. Planetary defence experts from the Agency's Space Safety programme worked with NASA and the international asteroid community to closely watch this object and refine its orbit, which was eventually determined to not pose a risk of Earth impact. Read details on this unusual campaign via ESA's Rocket Science blog and in news articles here and here.
Webb’s observations indicate that the asteroid measures roughly 60 meters (comparable to the height of a 15-story building).
The new observations from Webb not only provide unique information about 2024 YR4’s size, but can also complement ground-based observations of the object's position to help improve our understanding of the object’s orbit and future trajectory.
Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
[Image description: A collage of three images showing the black expanse of space. Two-thirds of the collage is taken up by the black background sprinkled with small, blurry galaxies in orange, blue, and white. There are two images in a column at the right side of the collage. On the right side of the main image, not far from the top, a very faint dot is outlined with a white square. At the right, there are two zoomed in views of this area. The top box is labeled NIRCam and shows a fuzzy dot at the center of the inset. The bottom box is labeled MIRI and shows a fuzzy pinkish dot.]
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By NASA
Explore This Section Webb News Latest News Latest Images Blog (offsite) 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 5 Min Read NASA Webb Explores Effect of Strong Magnetic Fields on Star Formation
An image of the Milky Way captured by the MeerKAT radio telescope array puts the James Webb Space Telescope’s image of the Sagittarius C region in context. Full image below. Credits:
NASA, ESA, CSA, STScI, SARAO, Samuel Crowe (UVA), John Bally (CU), Ruben Fedriani (IAA-CSIC), Ian Heywood (Oxford) Follow-up research on a 2023 image of the Sagittarius C stellar nursery in the heart of our Milky Way galaxy, captured by NASA’s James Webb Space Telescope, has revealed ejections from still-forming protostars and insights into the impact of strong magnetic fields on interstellar gas and the life cycle of stars.
“A big question in the Central Molecular Zone of our galaxy has been, if there is so much dense gas and cosmic dust here, and we know that stars form in such clouds, why are so few stars born here?” said astrophysicist John Bally of the University of Colorado Boulder, one of the principal investigators. “Now, for the first time, we are seeing directly that strong magnetic fields may play an important role in suppressing star formation, even at small scales.”
Detailed study of stars in this crowded, dusty region has been limited, but Webb’s advanced near-infrared instruments have allowed astronomers to see through the clouds to study young stars like never before.
“The extreme environment of the galactic center is a fascinating place to put star formation theories to the test, and the infrared capabilities of NASA’s James Webb Space Telescope provide the opportunity to build on past important observations from ground-based telescopes like ALMA and MeerKAT,” said Samuel Crowe, another principal investigator on the research, a senior undergraduate at the University of Virginia and a 2025 Rhodes Scholar.
Bally and Crowe each led a paper published in The Astrophysical Journal.
Image A: Milky Way Center (MeerKAT and Webb)
An image of the Milky Way captured by the MeerKAT (formerly the Karoo Array Telescope) radio telescope array puts the James Webb Space Telescope’s image of the Sagittarius C region in context. Like a super-long exposure photograph, MeerKAT shows the bubble-like remnants of supernovas that exploded over millennia, capturing the dynamic nature of the Milky Way’s chaotic core. At the center of the MeerKAT image the region surrounding the Milky Way’s supermassive black hole blazes bright. Huge vertical filamentary structures echo those captured on a smaller scale by Webb in Sagittarius C’s blue-green hydrogen cloud. NASA, ESA, CSA, STScI, SARAO, Samuel Crowe (UVA), John Bally (CU), Ruben Fedriani (IAA-CSIC), Ian Heywood (Oxford) Image B: Milky Way Center (MeerKAT and Webb), Labeled
The star-forming region Sagittarius C, captured by the James Webb Space Telescope, is about 200 light-years from the Milky Way’s central supermassive black hole, Sagittarius A*. The spectral index at the lower left shows how color was assigned to the radio data to create the image. On the negative end, there is non-thermal emission, stimulated by electrons spiraling around magnetic field lines. On the positive side, thermal emission is coming from hot, ionized plasma. For Webb, color is assigned by shifting the infrared spectrum to visible light colors. The shortest infrared wavelengths are bluer, and the longer wavelengths appear more red. NASA, ESA, CSA, STScI, SARAO, Samuel Crowe (UVA), John Bally (CU), Ruben Fedriani (IAA-CSIC), Ian Heywood (Oxford) Using Infrared to Reveal Forming Stars
In Sagittarius C’s brightest cluster, the researchers confirmed the tentative finding from the Atacama Large Millimeter Array (ALMA) that two massive stars are forming there. Along with infrared data from NASA’s retired Spitzer Space Telescope and SOFIA (Stratospheric Observatory for Infrared Astronomy) mission, as well as the Herschel Space Observatory, they used Webb to determine that each of the massive protostars is already more than 20 times the mass of the Sun. Webb also revealed the bright outflows powered by each protostar.
Even more challenging is finding low-mass protostars, still shrouded in cocoons of cosmic dust. Researchers compared Webb’s data with ALMA’s past observations to identify five likely low-mass protostar candidates.
The team also identified 88 features that appear to be shocked hydrogen gas, where material being blasted out in jets from young stars impacts the surrounding gas cloud. Analysis of these features led to the discovery of a new star-forming cloud, distinct from the main Sagittarius C cloud, hosting at least two protostars powering their own jets.
“Outflows from forming stars in Sagittarius C have been hinted at in past observations, but this is the first time we’ve been able to confirm them in infrared light. It’s very exciting to see, because there is still a lot we don’t know about star formation, especially in the Central Molecular Zone, and it’s so important to how the universe works,” said Crowe.
Magnetic Fields and Star Formation
Webb’s 2023 image of Sagittarius C showed dozens of distinctive filaments in a region of hot hydrogen plasma surrounding the main star-forming cloud. New analysis by Bally and his team has led them to hypothesize that the filaments are shaped by magnetic fields, which have also been observed in the past by the ground-based observatories ALMA and MeerKAT (formerly the Karoo Array Telescope).
“The motion of gas swirling in the extreme tidal forces of the Milky Way’s supermassive black hole, Sagittarius A*, can stretch and amplify the surrounding magnetic fields. Those fields, in turn, are shaping the plasma in Sagittarius C,” said Bally.
The researchers think that the magnetic forces in the galactic center may be strong enough to keep the plasma from spreading, instead confining it into the concentrated filaments seen in the Webb image. These strong magnetic fields may also resist the gravity that would typically cause dense clouds of gas and dust to collapse and forge stars, explaining Sagittarius C’s lower-than-expected star formation rate.
“This is an exciting area for future research, as the influence of strong magnetic fields, in the center of our galaxy or other galaxies, on stellar ecology has not been fully considered,” said Crowe.
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).
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View/Download the science paper led by Crowe from the The Astrophysical Journal.
Media Contacts
Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Leah Ramsay – lramsay@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
Christine Pulliam – cpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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Last Updated Apr 02, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
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By NASA
Based at NASA’s Johnson Space Center in Houston, the Astromaterials Research and Exploration Science Division, or ARES, curates the most extensive collection of extraterrestrial materials on Earth, ranging from microscopic cosmic dust particles to Apollo-era Moon rocks. Soon, ARES’ team of world-leading sample scientists hopes to add something new to its collection – lunar samples from the Moon’s South Pole region.
As the Artemis campaign sample curation lead, Dr. Juliane Gross is helping ARES and NASA prepare to collect and return those samples safely. “I’m responsible for representing the voice of the Moon rocks and advocating for their protection, preservation, and maintaining their integrity during the planning and execution of all stages of the different Artemis sample return missions,” she said.
Juliane Gross leads a geology lesson for Artemis II crew members as part of their field training in Iceland in 2024.NASA Her multifaceted role includes preparing the Johnson facility that will receive new lunar samples, developing curation strategies, and collaborating with mission teams to plan sampling operations, which encompass collection, handling, transport, and storage processes for all stages of Artemis missions. She trains program managers and engineers on the importance of sample return and teaches crew members how to identify lunar samples and collect them without contamination. She also works with the different programs and teams that oversee the vehicles used at different stages of lunar missions – collaborating with the human landing system team around tool storage and delivery to the lunar surface, the Orion Program to coordinate sample stowage for the return to Earth, and Exploration Ground Systems to plan sample recovery after splashdown.
Once samples are returned to Earth, Gross and the ARES curation team will conduct a preliminary examination of the materials and release a sample catalog from which members of the global scientific community may request loans to carry out their respective research.
Working across Artemis teams raised an unexpected but fun challenge for Gross – learning to communicate effectively with colleagues who have different academic and professional backgrounds. “Scientists like me speak a different language than engineers, and we all speak a different language than managers or the general public,” she said. “I have worked hard to find common vocabulary and to ‘translate’ science needs into the different types of languages that exist within the Artemis campaign. I’m trying to use our differences as strengths to enable mission success and to connect and build relationships with all these different teams through my love and passion for the Moon and rocks from the Moon.”
That passion emerged shortly after Gross completed her Ph.D. in geology, while working on lunar samples with the Lunar and Planetary Institute. She went on to become a research scientist with the American Museum of Natural History in New York, and then a tenured professor of planetary sciences at Rutgers University in Piscataway, New Jersey.
In 2019, NASA asked Gross to join the Apollo Next Generation Sample Analysis Program. Under the program, NASA preserved some of the 382 kilograms of lunar samples returned by Apollo missions, keeping them sealed for future generations to open and analyze. “NASA had the foresight to understand that technology would evolve and our level of sophistication for handling and examining samples would greatly increase,” Gross said.
She and two other scientists had the incredible opportunity to open and examine two samples returned by Apollo 17. Their work served as a practice run for Artemis sample returns while building upon the fundamental insights into the shared origin and history of Earth and the Moon that scientists previously derived from other Apollo samples. For example, the team extracted gas from one sample that will provide information about the volatiles that future lunar missions may encounter around the Moon’s South Pole.
“The Apollo Next Generation Sample Analysis Program linked the first generation of lunar explorers from Apollo with future explorers of the Moon with Artemis,” Gross said. “I’m very proud to have played such an important role in this initiative that now feeds forward to Artemis.”
Juliane Gross examines lunar samples returned by Apollo 17 in Johnson Space Center’s Lunar Sample Laboratory Facility. NASA Gross’ connection with NASA began even earlier in her career. She was selected to join the agency-sponsored Antarctic Search for Meteorites team and lived in the deep ice fields of Antarctica for two months with seven other people. “We lived in tiny two-person tents without any support and recovered a total of 263 space rocks under challenging conditions,” she said. “I experienced the powerful forces of Antarctica and traveled 332 miles on skidoos. My body changed in the cold – I stuffed my face with enough butter, chocolate, and peanut M&Ms to last a lifetime and yet I lost weight.”
This formative experience taught Gross to find and celebrate beauty, even in her toughest moments. “I drank tea made with Antarctic glacier ice that is thousands to millions of years old. I will never forget the beautiful bell-like sounds that snow crystals make when being blown across the ice, the rainbow-sparkling ice crystals on a really cold day, the vast expanses of ice sheets looking like oceans frozen in eternity, and the icy bite of the wind on any unprotected skin that made me feel so alive and reminded me how vulnerable and precious life is,” she said. “And I will never ever forget the thrill and utter joy of finding a meteorite that you know no one on this planet has ever seen before you.”
Gross ultimately received the Antarctica Service Medal of the United States Armed Forces from the U.S. Department of Defense for her work.
Juliane Gross returns to McMurdo Station in Antarctica after working in the deep field for two months as part of the Antarctic Search for Meteorites team.Image courtesy of Juliane Gross Transitioning from full-time academia to her current position at NASA has been a big adjustment for Gross, but she has learned to love the change and the growth opportunities that come with it. “Being part of this incredible moment in history when we are about to return to the Moon with Artemis, our Apollo of today, feels so special and humbling that it made the transition easier,” she said.
The job has also increased Gross’ love and excitement for space exploration and reminds her every day why sample return missions are important. “The Moon is a museum of planetary history,” she said. “It has recorded and preserved the changes that affected the Earth-Moon system and is the best and most accessible place in the solar system to study planet-altering processes that have affected our corner of the universe.”
Still, “The Moon is only our next frontier,” she said. “Keep looking up and never give up. Ad astra!”
Watch below to learn about NASA’s rich history of geology training and hear how scientists and engineers are getting ready to bring back samples that will help us learn about the origins of our solar system.
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By NASA
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 3 min read
Visiting Mars on the Way to the Outer Solar System
Written by Roger Wiens, Principal Investigator, SuperCam instrument / Co-Investigator, SHERLOC instrument at Purdue University
A portion of the “Sally’s Cove” outcrop where the Perseverance rover has been exploring. The radiating lines in the rock on the left of the image may indicate that it is a shatter cone, showing the effects of the shock wave from a nearby large impact. The image was taken by Mastcam-Z’s left camera on March 21, 2025 (Sol 1452, or Martian day 1,452 of the Mars 2020 mission) at the local mean solar time of 12:13:44. Mastcam-Z is a pair of cameras located high on the rover’s mast. This image was voted by the public as “Image of the week.” NASA/JPL-Caltech/ASU Recently Mars has had a few Earthly visitors. On March 1, NASA’s Europa Clipper flew within 550 miles (884 kilometers) of the Red Planet’s surface on its way out to Jupiter. On March 12, the European Space Agency’s Hera spacecraft flew within about 3,100 miles (5,000 kilometers) of Mars, and only 300 kilometers from its moon, Deimos. Hera is on its way to study the binary asteroid Didymos and its moon Dimorphos. Next year, in May 2026, NASA’s Psyche mission is scheduled to buzz the Red Planet on its way to the metal-rich asteroid 16 Psyche, coming within a few thousand kilometers.
Why all these visits to Mars? You might at first think that they’re using Mars as an object of opportunity for their cameras, and you would be partially right. But Mars has more to give these missions than that. The main reason for these flybys is the extra speed that Mars’ velocity around the Sun can give them. The idea that visiting a planet can speed up a spacecraft is not all that obvious, because the same gravity that attracts the spacecraft on its way towards the planet will exert a backwards force as the spacecraft leaves the planet.
The key is in the direction that it approaches and leaves the planet. If the spacecraft leaves Mars heading in the direction that Mars is traveling around the Sun, it will gain speed in that direction, slingshotting it farther into the outer solar system. A spacecraft can typically gain several percent of its speed by performing such a slingshot flyby. The closer it gets to the planet, the bigger the effect. However, no mission wants to be slowed by the upper atmosphere, so several hundred kilometers is the closest that a mission should go. And the proximity to the planet is also affected by the exact direction the spacecraft needs to go when it leaves Mars.
Clipper’s Mars flyby was a slight exception, slowing down the craft — by about 1.2 miles per second (2 kilometers per second) — to steer it toward Earth for a second gravity assist in December 2026. That will push the spacecraft the rest of the way to Jupiter, for its 2030 arrival.
While observing Mars is not the main reason for their visits, many of the visiting spacecraft take the opportunity to use their cameras either to perform calibrations or to study the Red Planet and its moons.
During Clipper’s flyby over sols 1431-1432, Mastcam-Z was directed to watch the skies for signs of the interplanetary visitor. Clipper’s relatively large solar panels could have reflected enough sunlight for it to be seen in the Mars night sky, much as we can see satellites overhead from Earth. Unfortunately, the spacecraft entered the shadow of Mars just before it came into potential view above the horizon from Perseverance’s vantage point, so the sighting did not happen. But it was worth a try.
Meanwhile, back on the ground, Perseverance is performing something of a cliff-hanger. “Sally’s Cove” is a relatively steep rock outcrop in the outer portion of Jezero crater’s rim just north of “Broom Hill.” Perseverance made an approach during March 19-23, and has been exploring some dark-colored rocks along this outcrop, leaving the spherules behind for the moment. Who knows what Perseverance will find next?
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Last Updated Mar 28, 2025 Related Terms
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