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By NASA
Explore This Section Earth Earth Observer Editor’s Corner Feature Articles Meeting Summaries News Science in the News Calendars In Memoriam Announcements More Archives Conference Schedules Style Guide 13 min read
The Earth Observer Editor’s Corner: July–September 2025
NOTE TO READERS: After more than three decades associated with or directly employed by NASA, Steve Platnick [GSFC—Deputy Director for Atmospheres, Earth Sciences Division] stepped down effective August 8, 2025. Steve began his civil servant career at GSFC in 2002, but his GSFC association went back to 1993, first as a contractor and then as one of the earliest employees of the Joint Center for Earth Systems Technology (JCET). During his time at NASA, Steve played an integral role in the sustainability and advancement of NASA’s Earth Observing System platforms and data. He was actively involved in the Moderate Resolution Imaging Spectroradiometer (MODIS) Science Team, where he helped advance several key components of the MODIS instrument. He was also the NASA Lead/co-Lead for the Suomi National Polar-orbiting Partnership (Suomi NPP), Atmosphere Discipline from 2012–2020 where he focused on operational cloud optical and microphysical products.
In 2008, Steve became the Earth Observing System (EOS) Senior Project Scientist. In this role, he led the EOS Project Science Office that supported airborne sensors, ground networks, and calibration labs. The Kudos article titled “Steve Platnick Steps Down from NASA After 34 Years of Service” includes a more detailed account of Steve’s career and includes a list of awards he has received.
Steve’s departure leaves a vacancy in the author’s chair for “The Editor’s Corner” – another role Steve filled as EOS Senior Project Scientist. Barry Lefer [NASA Headquarters—Associate Director of Research, Earth Science Division] graciously agreed to serve as guest author of the editorial in the current compilation. I want to thank Steve for all his support for The Earth Observer over the years and thank Barry for stepping in as the author of “The Editor’s Corner” for the time being.
–Alan Ward, Executive Editor, The Earth Observer
I begin this editorial with news of a successful Earth science launch. At 5:40 PM Indian Standard Time (IST), or 8:10 AM Eastern Daylight Time (EDT), on July 30, 2025, the joint NASA–Indian Space Research Organization (ISRO) Synthetic Aperture Radar, or NISAR, mission launched from the Satish Dhawan Space Centre on India’s southeastern coast aboard an ISRO Geosynchronous Satellite Launch Vehicle (GSLV) rocket 5. The ISRO ground controllers began communicating with NISAR about 20 minutes after launch, at just after 8:29 AM EDT, and confirmed it is operating as expected.
NISAR will use two different radar frequencies (L-band SAR and S-band SAR) to penetrate clouds and forest canopies. Including L-band and S-band radars on one satellite is an evolution in SAR airborne and space-based missions that, for NASA, started in 1978 with the launch of Seasat. In 2012, ISRO began launching SAR missions starting with Radar Imaging Satellite (RISAT-1), followed by RISAT-1A in 2022, to support a wide range of applications in India.
Combining the data from these two radars will allow researchers to systematically and globally map Earth – measuring changes of our planet’s surface down to a centimeter (~0.4 inches). With this detailed view, researchers will have an unprecedented ability to observe and measure complex processes from ecosystem disturbances to natural hazards to groundwater issues. All NISAR science data will be freely available and open to the public.
Following the successful launch, NISAR entered an approximately 90-day commissioning phase to test out systems before science operations begin. A key milestone of that phase was the completion of the deployment of the 39-ft (12-m) radar antenna reflector on August 15 – see Video. The process began on August 9, when the satellite’s boom, which had been tucked close to its main body, started unfolding one joint at a time until it was fully extended about four days later. The reflector assembly is mounted at the end of the boom. On August 15, small explosive bolts that held the reflector assembly in place were fired, enabling the antenna to begin a process called the bloom – its unfurling by the release of tension stored in its flexible frame while stowed like an umbrella. Subsequent activation of motors and cables pulled the antenna into its final, locked position.
Video: NISAR mission team members at NASA JPL, working with colleagues in India, executed the deployment of the satellite’s radar antenna reflector on Aug. 15, 2025. About 39 feet (12 meters) in diameter, the reflector directs microwave pulses from NISAR’s two radars toward Earth and receives the return signals. Credit: NASA/JPL-Caltech The radar reflector will be used to direct and receive microwave signals from the two radars. By interpreting the differences between the L-band and S-band measurements, researchers will be able to discern characteristics about the surface below. As NISAR passes over the same locations twice every 12 days, scientists can evaluate how those characteristics have changed over time to reveal new insights about Earth’s dynamic surfaces.
With the radar reflector now in full bloom, scientists have turned their attention to tuning and testing the radar and preparing NISAR for Science Operations, which are anticipated to start around the beginning of November. Congratulations to the NISAR team on a successful launch and deployment of the radar reflector. Along with the science community, I am excited to see what new discoveries will result from the data collected by the first Earth System Observatory mission.
Turning now to news from active missions, the Soil Moisture Active Passive (SMAP) mission has collected over 10 years of global L-band radiometry observations that have resulted in surface soil moisture, vegetation optical depth (VOD), and freeze/thaw state estimates that outperform past and current products. A decade of SMAP soil moisture observations has led to scientific achievements, including quantifying the linkages of the three main metabolic cycles (e.g., carbon, water, and energy) on land. The data have been widely used by the Earth system science community to improve drought assessments and flood prediction as well as the accuracy of numerical weather prediction models.
SMAP’s Early Adopter program has helped connect SMAP data with people and organizations that need it. The program has increased the awareness of SMAP mission products, broadened the user community, increased collaboration with potential users, improved knowledge of SMAP data product capabilities, and expedited the distribution and uses of mission products for a suite of 16 products available. For example, the L-band VOD, which is related to water content in vegetation, is being used to better understand water exchanges in the soil–vegetation–atmosphere continuum.
The SMAP Active–Passive (AP) algorithm – based on data from SMAP and the European Copernicus Program Sentinel-1 C-band synthetic aperture radar (SAR) – will be adapted to work with L-band data from the newly launched NISAR mission. The result will be estimates of global soil moisture at a spatial resolution of 1 km (0.62 mi) or better approximately once per week.
In addition, the data collected during the SMAP mission would be continued and further enhanced by the European Union’s Copernicus Imaging Microwave Radiometer (CIMR) mission if it launches. This proposed multichannel microwave radiometry observatory includes L-band and four other microwave channels sharing a large mesh reflector – like the one used with SMAP. The plan calls for CIMR to follow a similar approach as SMAP for RFI detection and meet the instrument thermal noise and data latency of SMAP for next-mission desired characteristics.
To learn more about what SMAP has accomplished see “A Decade of Global Water Cycle Monitoring: NASA Soil Moisture Active Passive Mission.”
NASA’s Orbiting Carbon Observatory-2 (OCO-2) has been the “gold standard” for atmospheric carbon dioxide (CO2) observations from space for over a decade. The data returned from OCO-2 provide insights into plant health, forest management, forecasting crop yields, fire-risk models, and anticipating droughts.
OCO-3, constructed from spare parts left after OCO-2, was launched to the International Space Station (ISS) in 2019, where it has operated for over five years. OCO-3 extends the global CO2 measurement record while adding new capabilities made possible by being on ISS (e.g., detailed views of urban and tropical regions).
The overarching OCO mission hasn’t just about been about data and hardware. Although both those elements are parts of the story, the human stories woven through the mission’s successes and setbacks are really what holds the mission together. The feature, “A Tapestry of Tales: 10th Anniversary Reflections from NASA’s OCO-2 Mission,” sheds light on some of these personal stories from the OCO-2 and OCO-3 missions.
The individual tales contained in this article reveal the grit and determination behind the scenes of the success of OCO-2 and OCO-3, from the anxiety and excitement surrounding the launch of OCO-2, to moments of fieldwork in the Nevada desert, to internships where wildfire responders turned to OCO-2 data to improve fire-risk models. Taken together, these stories form a “tapestry” that reveals how the OCO-2 and OCO-3 missions continue to illuminate the dynamics of Earth’s atmosphere – one breath at a time.
These personal perspectives underscore that science is not just numbers; it’s people pushing boundaries, navigating failure, and inspiring ways to make our planet safer and healthier. In a time such as this, this is an important reminder.
The joint NASA–U.S. Geological Survey (USGS) Landsat program has been a cornerstone of Earth observation for over 50 years. On July 13, Landsat 9 collected its millionth image: a stunning shot of the Arctic National Wildlife Refuge in Alaska – see Figure. Landsat 9, the most recent satellite in the Landsat series, orbits Earth alongside Landsat 8. Together, these satellites collect invaluable data about Earth’s changing land surface every eight days.
Figure: This Landsat 9 image showing the Beaufort Sea shoreline off Alaska and Canada is just one of the scenes captured and processed on July 13, 2025— the same day the USGS EROS archive reached a milestone of one million Landsat 9 Level-1 products. This false color image was made with bands 6, 5, and 4 from the Operational Land Imager. This remote area allows the pristine wilderness environment to support a diverse wildlife and unique ecosystem that includes various species of mammals, birds, and fish. Landsat Level-1 products from Landsat 1 through Landsat 9 can be downloaded at no charge from a number of systems – visit the Landsat Data Access webpage to learn more. Credit: Public Domain After collecting more than 3.3 million images over the course of more than 26 years in orbit, Landsat 7 was decommissioned on June 4, 2025. A YouTube video released at the time of decommissioning provides a concise visual summary of the Landsat 7 mission’s achievements – and the technical challenges overcome. In addition, The Earth Observer did a feature for the 20th anniversary of Landsat 7 in the July–August 2019 issue, called “The Living Legacy of Landsat 7: Still Going Strong After 20 Years in Orbit” [Volume 31, Issue 4, pp. 4–14] that is a useful resource to learn more about the history and achievements (through 20 years) of the mission.
One of the strengths of the Landsat program is its potential for data integration with other satellites. The Harmonized Landsat and Sentinel-2 (HLS) product exemplifies this collaborative approach by combining data from Landsat 8 and 9 with data from the European Space Agency’s Copernicus Sentinel-2 A, B, and C missions. Whereas Landsat alone has a repeat time of eight days (i.e., combining Landsat 8 and 9 data); the combined HLS dataset provides imagery for the same location on Earth every 1.6 days – enabling researchers to monitor short-term changes in Earth’s land surface much more effectively than using Landsat or Sentinel-2 data alone.
HLS became one of the most-downloaded NASA data products in fiscal year 2024, with continued growth on the horizon. In February 2025, the program expanded with nine new vegetation indices based on HLS data, with historical processing back to 2013 scheduled for completion by early 2026. Low-latency HLS products will also be available in late 2026. For the full story of how HLS came to be – see the feature: “Harmonized Landsat and Sentinel-2: Collaboration Drives Innovation.”
Following a 13-month hibernation, the Global Ecosystem Dynamics Investigation (GEDI) mission was reinstalled to its original location aboard the ISS and resumed operations on April 22, 2024. Since this storage period, GEDI’s lasers have been operating nominally and the mission has continued to produce high-quality observations of the Earth’s three-dimensional structure, amassing 33 billion land surface returns as of November 27, 2024.
The mission team has been actively processing and releasing post-storage data to the public, with Version 2.1 – GEDI L1B, L2A, L2B, and L4A data products, which include data through November 2024, all available for download. The new L4C footprint-level Waveform Structural Complexity Index (WSCI) product using pre-storage data has also been released. Looking ahead, the team is preparing Version 3.0 (V3) of all data products, which will incorporate post-storage data while improving quality filtering, geolocation accuracy, and algorithm performance.
The 2025 GEDI Science Team Meeting (STM) brought together the mission science team, competed science team, representatives from the distributed active archive centers (DAACs), collaborators, stakeholders, and data users. Notably, it marked the first in-person gathering of the second competed science team, who shared updates on their research projects. The STM held an important space for brainstorming, knowledge-sharing, and discussion as the GEDI mission continues to flourish in its second epoch. To learn more, see “Summary of the 2025 GEDI Science Team Meeting.”
Shifting focus to the boreal forests of North America, the NASA Arctic–Boreal Vulnerability Experiment (ABoVE) is now in its final year, marking the end of a decade-long scientific endeavor that has transformed our understanding of environmental change in Alaska and western Canada. This ambitious campaign, funded primarily by NASA’s Terrestrial Ecology Program, has successfully progressed through three distinct phases: ecosystem dynamics (2015–2018), ecosystem services (2017–2022), and the current analysis and synthesis phase (2023–present).
As ABoVE approaches its conclusion, the program has grown to encompass 67 NASA-funded projects with over 1000 participating researchers – a testament to the collaborative scale required to address complex Arctic–boreal ecosystem questions. The program’s integrated approach, combining field research, airborne campaigns, and satellite remote sensing, has generated unprecedented insights into how environmental changes in these northern regions affect both vulnerable ecosystems and society.
The recent 11th – and final – ABoVE Science Team Meeting was an opportunity to showcase the program’s evolution from data collection to synthesis, highlighting successful community engagement initiatives, cutting-edge research on carbon dynamics and ecosystem responses, and innovative science communication strategies that have made this complex research accessible to diverse audiences. With synthesis activities now underway, ABoVE is positioned to deliver comprehensive insights that will inform Arctic and boreal research for years to come. To learn more, see “Summary of the 11th and Final ABoVE Science Team Meeting.”
Last but certainly not least, I want to both recognize and congratulate Compton J. Tucker [GSFC—Senior Researcher]. Compton retired from NASA in March 2025 after 48 years of public service, and then in April, was among 149 newly elected members to the National Academy of Sciences (NAS) – which is one of the highest honors in American science. This recognition from NAS brings Compton’s career full circle. He came to GSFC as a NAS postdoc before joining NASA as a civil servant. Compton is a pioneer in the field of satellite-based environmental analysis, using data from various Landsat missions and from the National Oceanographic and Atmospheric Administration’s (NOAA) Advanced Very High Resolution Radiometer (AVHRR) instrument. His research has focused on global photosynthesis on land, determining land cover, monitoring droughts and food security, and evaluating ecologically coupled disease outbreaks. The Kudos, “Compton J. Tucker Retires from NASA and is Named NAS Fellow,” provides more details about Compton’s research achievements and all of the other scientific awards and honors received throughout his career.
Barry Lefer
Associate Director of Research, Earth Science Division
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Last Updated Sep 10, 2025 Related Terms
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By NASA
Explore Webb 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 Webb Timeline Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Science Explainers 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 Webb’s First Images Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning 5 Min Read Glittering Glimpse of Star Birth From NASA’s Webb Telescope
Webb captured this sparkling scene of star birth in Pismis 24. Full image and caption below. Credits:
Image: NASA, ESA, CSA, STScI; Image Processing: A. Pagan (STScI) This is a sparkling scene of star birth captured by NASA’s James Webb Space Telescope. What appears to be a craggy, starlit mountaintop kissed by wispy clouds is actually a cosmic dust-scape being eaten away by the blistering winds and radiation of nearby, massive, infant stars.
Called Pismis 24, this young star cluster resides in the core of the nearby Lobster Nebula, approximately 5,500 light-years from Earth in the constellation Scorpius. Home to a vibrant stellar nursery and one of the closest sites of massive star birth, Pismis 24 provides rare insight into large and massive stars. Its proximity makes this region one of the best places to explore the properties of hot young stars and how they evolve.
At the heart of this glittering cluster is the brilliant Pismis 24-1. It is at the center of a clump of stars above the jagged orange peaks, and the tallest spire is pointing directly toward it. Pismis 24-1 appears as a gigantic single star, and it was once thought to be the most massive known star. Scientists have since learned that it is composed of at least two stars, though they cannot be resolved in this image. At 74 and 66 solar masses, respectively, the two known stars are still among the most massive and luminous stars ever seen.
Image A: Pismis 24 (NIRCam Image)
Webb captured this sparkling scene of star birth in Pismis 24, a young star cluster about 5,500 light-years from Earth in the constellation Scorpius. This region is one of the best places to explore the properties of hot young stars and how they evolve. Image: NASA, ESA, CSA, STScI; Image Processing: A. Pagan (STScI) Captured in infrared light by Webb’s NIRCam (Near-Infrared Camera), this image reveals thousands of jewel-like stars of varying sizes and colors. The largest and most brilliant ones with the six-point diffraction spikes are the most massive stars in the cluster. Hundreds to thousands of smaller members of the cluster appear as white, yellow, and red, depending on their stellar type and the amount of dust enshrouding them. Webb also shows us tens of thousands of stars behind the cluster that are part of the Milky Way galaxy.
Super-hot, infant stars –some almost 8 times the temperature of the Sun – blast out scorching radiation and punishing winds that are sculpting a cavity into the wall of the star-forming nebula. That nebula extends far beyond NIRCam’s field of view. Only small portions of it are visible at the bottom and top right of the image. Streamers of hot, ionized gas flow off the ridges of the nebula, and wispy veils of gas and dust, illuminated by starlight, float around its towering peaks.
Dramatic spires jut from the glowing wall of gas, resisting the relentless radiation and winds. They are like fingers pointing toward the hot, young stars that have sculpted them. The fierce forces shaping and compressing these spires cause new stars to form within them. The tallest spire spans about 5.4 light-years from its tip to the bottom of the image. More than 200 of our solar systems out to Neptune’s orbit could fit into the width its tip, which is 0.14 lightyears.
In this image, the color cyan indicates hot or ionized hydrogen gas being heated up by the massive young stars. Dust molecules similar to smoke here on Earth are represented in orange. Red signifies cooler, denser molecular hydrogen. The darker the red, the denser the gas. Black denotes the densest gas, which is not emitting light. The wispy white features are dust and gas that are scattering starlight.
Video A: Expedition to Star Cluster Pismis 24
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This scientific visualization takes viewers on a journey to a glittering young star cluster called Pismis 24. NASA’s James Webb Space Telescope captured this fantastical scene in the heart of the Lobster Nebula, approximately 5,500 light-years from Earth. Video: NASA, ESA, CSA, STScI, Leah Hustak (STScI), Christian Nieves (STScI); Image Processing: Alyssa Pagan (STScI); Script Writer: Frank Summers (STScI); Narration: Frank Summers (STScI); Music: Christian Nieves (STScI); Audio: Danielle Kirshenblat (STScI); Producer: Greg Bacon (STScI); Acknowledgment: VISTA Video B: Zoom to Pismis 24
This zoom-in video shows the location of the young star cluster Pismis 24 on the sky. It begins with a ground-based photo of the constellation Scorpius by the late astrophotographer Akira Fujii. The sequence closes in on the Lobster Nebula, using views from the Digitized Sky Survey. As the video homes in on a select portion, it fades to a VISTA image in infrared light. The zoom continues in to the region around Pismis 24, where it transitions to the stunning image captured by NASA’s James Webb Space Telescope in near-infrared light.
Video: NASA, ESA, CSA, STScI, Alyssa Pagan (STScI); Narration: Frank Summers (STScI); Script Writer: Frank Summers (STScI); Music: Christian Nieves (STScI); Audio: Danielle Kirshenblat (STScI); Producer: Greg Bacon (STScI); Acknowledgment: VISTA, Akira Fujii, DSS 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:
https://science.nasa.gov/webb
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Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Ann Jenkins – jenkins@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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NASA/Nichole Ayers On July 26, 2025, NASA astronaut Nichole Ayers took this long-exposure photograph – taken over 31 minutes from a window inside the International Space Station’s Kibo laboratory module – capturing the circular arcs of star trails.
In its third decade of continuous human presence, the space station has a far-reaching impact as a microgravity lab hosting technology, demonstrations, and scientific investigations from a range of fields. The research done on the orbiting laboratory will inform long-duration missions like Artemis and future human expeditions to Mars.
Image credit: NASA/Nichole Ayers
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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 Universe Uncovered Hubble’s Partners in Science AI and Hubble Science Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Astronaut Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts Multimedia Images Videos Sonifications Podcasts e-Books Online Activities 3D Hubble Models Lithographs Fact Sheets Posters Hubble on the NASA App Glossary News Hubble News Social Media Media Resources More 35th Anniversary Online Activities 2 min read
Hubble Homes in on Galaxy’s Star Formation
This NASA/ESA Hubble Space Telescope image features the asymmetric spiral galaxy Messier 96. ESA/Hubble & NASA, F. Belfiore, D. Calzetti This NASA/ESA Hubble Space Telescope image features a galaxy whose asymmetric appearance may be the result of a galactic tug of war. Located 35 million light-years away in the constellation Leo, the spiral galaxy Messier 96 is the brightest of the galaxies in its group. The gravitational pull of its galactic neighbors may be responsible for Messier 96’s uneven distribution of gas and dust, asymmetric spiral arms, and off-center galactic core.
This asymmetric appearance is on full display in the new Hubble image that incorporates data from observations made in ultraviolet, near infrared, and visible/optical light. Earlier Hubble images of Messier 96 were released in 2015 and 2018. Each successive image added new data, building up a beautiful and scientifically valuable view of the galaxy.
The 2015 image combined two wavelengths of optical light with one near infrared wavelength. The optical light revealed the galaxy’s uneven form of dust and gas spread asymmetrically throughout its weak spiral arms and its off-center core, while the infrared light revealed the heat of stars forming in clouds shaded pink in the image.
The 2018 image added two more optical wavelengths of light along with one wavelength of ultraviolet light that pinpointed areas where high-energy, young stars are forming.
This latest version offers us a new perspective on Messier 96’s star formation. It includes the addition of light that reveals regions of ionized hydrogen (H-alpha) and nitrogen (NII). This data helps astronomers determine the environment within the galaxy and the conditions in which stars are forming. The ionized hydrogen traces ongoing star formation, revealing regions where hot, young stars are ionizing the gas. The ionized nitrogen helps astronomers determine the rate of star formation and the properties of gas between stars, while the combination of the two ionized gasses helps researchers determine if the galaxy is a starburst galaxy or one with an active galactic nucleus.
The bubbles of pink gas in this image surround hot, young, massive stars, illuminating a ring of star formation in the galaxy’s outskirts. These young stars are still embedded within the clouds of gas from which they were born. Astronomers will use the new data in this image to study how stars are form within giant dusty gas clouds, how dust filters starlight, and how stars affect their environments.
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This graphic features data from NASA’s Chandra X-ray Observatory of the Cassiopeia A (Cas A) supernova remnant that reveals that the star’s interior violently rearranged itself mere hours before it exploded. The main panel of this graphic is Chandra data that shows the location of different elements in the remains of the explosion: silicon (represented in red), sulfur (yellow), calcium (green) and iron (purple). The blue color reveals the highest-energy X-ray emission detected by Chandra in Cas A and an expanding blast wave. The inset reveals regions with wide ranges of relative abundances of silicon and neon. This data, plus computer modeling, reveal new insight into how massive stars like Cas A end their lives.X-ray: NASA/CXC/Meiji Univ./T. Sato et al.; Image Processing: NASA/CXC/SAO/N. Wolk The inside of a star turned on itself before it spectacularly exploded, according to a new study from NASA’s Chandra X-ray Observatory. Today, this shattered star, known as the Cassiopeia A supernova remnant, is one of the best-known, well-studied objects in the sky.
Over three hundred years ago, however, it was a giant star on the brink of self-destruction. The new Chandra study reveals that just hours before it exploded, the star’s interior violently rearranged itself. This last-minute shuffling of its stellar belly has profound implications for understanding how massive stars explode and how their remains behave afterwards.
Cassiopeia A (Cas A for short) was one of the first objects the telescope looked at after its launch in 1999, and astronomers have repeatedly returned to observe it.
“It seems like each time we closely look at Chandra data of Cas A, we learn something new and exciting,” said Toshiki Sato of Meiji University in Japan who led the study. “Now we’ve taken that invaluable X-ray data, combined it with powerful computer models, and found something extraordinary.”
As massive stars age, increasingly heavy elements form in their interiors by nuclear reactions, creating onion-like layers of different elements. Their outer layer is mostly made of hydrogen, followed by layers of helium, carbon and progressively heavier elements – extending all the way down to the center of the star.
Once iron starts forming in the core of the star, the game changes. As soon as the iron core grows beyond a certain mass (about 1.4 times the mass of the Sun), it can no longer support its own weight and collapses. The outer part of the star falls onto the collapsing core, and rebounds as a core-collapse supernova.
The new research with Chandra data reveals a change that happened deep within the star at the very last moments of its life. After more than a million years, Cas A underwent major changes in its final hours before exploding.
“Our research shows that just before the star in Cas A collapsed, part of an inner layer with large amounts of silicon traveled outwards and broke into a neighboring layer with lots of neon,” said co-author Kai Matsunaga of Kyoto University in Japan. “This is a violent event where the barrier between these two layers disappears.”
This upheaval not only caused material rich in silicon to travel outwards; it also forced material rich in neon to travel inwards. The team found clear traces of these outward silicon flows and inward neon flows in the remains of Cas A’s supernova remnant. Small regions rich in silicon but poor in neon are located near regions rich in neon and poor in silicon.
The survival of these regions not only provides critical evidence for the star’s upheaval, but also shows that complete mixing of the silicon and neon with other elements did not occur immediately before or after the explosion. This lack of mixing is predicted by detailed computer models of massive stars near the ends of their lives.
There are several significant implications for this inner turmoil inside of the doomed star. First, it may directly explain the lopsided rather than symmetrical shape of the Cas A remnant in three dimensions. Second, a lopsided explosion and debris field may have given a powerful kick to the remaining core of the star, now a neutron star, explaining the high observed speed of this object.
Finally, the strong turbulent flows created by the star’s internal changes may have promoted the development of the supernova blast wave, facilitating the star’s explosion.
“Perhaps the most important effect of this change in the star’s structure is that it may have helped trigger the explosion itself,” said co-author Hiroyuki Uchida, also of Kyoto University. “Such final internal activity of a star may change its fate—whether it will shine as a supernova or not.”
These results have been published in the latest issue of The Astrophysical Journal and are available online.
To learn more about Chandra, visit:
https://science.nasa.gov/chandra
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
This release features a composite image of Cassiopeia A, a donut-shaped supernova remnant located about 11,000 light-years from Earth. Included in the image is an inset closeup, which highlights a region with relative abundances of silicon and neon.
Over three hundred years ago, Cassiopeia A, or Cas A, was a star on the brink of self-destruction. In composition it resembled an onion with layers rich in different elements such as hydrogen, helium, carbon, silicon, sulfur, calcium, and neon, wrapped around an iron core. When that iron core grew beyond a certain mass, the star could no longer support its own weight. The outer layers fell into the collapsing core, then rebounded as a supernova. This explosion created the donut-like shape shown in the composite image. The shape is somewhat irregular, with the thinner quadrant of the donut to the upper left of the off-center hole.
In the body of the donut, the remains of the star’s elements create a mottled cloud of colors, marbled with red and blue veins. Here, sulfur is represented by yellow, calcium by green, and iron by purple. The red veins are silicon, and the blue veins, which also line the outer edge of the donut-shape, are the highest energy X-rays detected by Chandra and show the explosion’s blast wave.
The inset uses a different color code and highlights a colorful, mottled region at the thinner, upper left quadrant of Cas A. Here, rich pockets of silicon and neon are identified in the red and blue veins, respectively. New evidence from Chandra indicates that in the hours before the star’s collapse, part of a silicon-rich layer traveled outwards, and broke into a neighboring neon-rich layer. This violent breakdown of layers created strong turbulent flows and may have promoted the development of the supernova’s blast wave, facilitating the star’s explosion. Additionally, upheaval in the interior of the star may have produced a lopsided explosion, resulting in the irregular shape, with an off-center hole (and a thinner bite of donut!) at our upper left.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Corinne Beckinger
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
corinne.m.beckinger@nasa.gov
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Last Updated Aug 28, 2025 EditorLee MohonContactCorinne M. Beckingercorinne.m.beckinger@nasa.govLocationMarshall Space Flight Center Related Terms
Chandra X-Ray Observatory General Marshall Astrophysics Marshall Space Flight Center Supernova Remnants Supernovae The Universe Explore More
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