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By NASA
Dr. Steven “Steve” Platnick took the NASA agency Deferred Resignation Program (DRP). His last work day was August 8, 2025. Steve spent more than three decades at, or associated with, NASA. While he began his civil servant career at the NASA’s Goddard Space Flight Center (GSFC) in 2002, his Goddard 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), a cooperative agreement between the University of Maryland, Baltimore County (UMBC) and GSFC’s Earth Science Division. At JCET Steve helped lead the development of the Atmosphere Physics Track curricula. Previously, he had held an NRC post-doctoral fellow at the NASA’s Ames Research Center. Along with his research work on cloud remote sensing from satellite and airborne sensors, Steve served as the Deputy Director for Atmospheres in GSFC’s Earth Sciences Division from January 2015–July 2024.
Dr. Steve Platnick Image credit: NASA During his time at NASA, Steve played an integral role in the sustainability and advancement of NASA’s Earth Observing System platforms and data. In 2008, he took over as the Earth Observing System (EOS) Senior Project Scientist from Michael King. In this role, he led the EOS Project Science Office, which included support for related EOS facility airborne sensors, ground networks, and calibration labs. The office also supported The Earth Observer newsletter, the NASA Earth Observatory, and other outreach and exhibit activities on behalf of NASA Headquarter’s Earth Science Division and Science Mission Directorate (further details below). From January 2003 – February 2010, Steve served as the Aqua Deputy Project Scientist.
Improving Imager Cloud Algorithms
Steve was actively involved in the Moderate Resolution Imaging Spectroradiometer (MODIS) Science Team serving as the Lead for the MODIS Atmosphere Discipline Team (cloud, aerosol and clear sky products) since 2008 and as the NASA Suomi National Polar-orbiting Partnership (Suomi NPP)/JPSS Atmosphere Discipline Lead/co-Lead from 2012–2020. His research team enhanced, maintained, and evaluated MODIS and Visible Infrared Imaging Radiometer Suite (VIIRS) cloud algorithms that included Level-2 (L2) Cloud Optical/Microphysical Properties components (MOD06 and MYD06 for MODIS on Terra and Aqua, respectively) and the Atmosphere Discipline Team Level-3 (L3) spatial/temporal products (MOD08, MYD08). The L2 cloud algorithms were developed to retrieve thermodynamic phase, optical thickness, effective particle radius, and derived water path for liquid and ice clouds, among other associated datasets. Working closely with longtime University of Wisconsin-Madison colleagues, the team also developed the CLDPROP continuity products designed to bridge the MODIS and VIIRS cloud data records by addressing differences in the spectral coverage between the two sensors; this product is currently in production for VIIRS on Suomi NPP and NOAA-20, as well as MODIS Aqua. The team also ported their CLDPROP code to Geostationary Operational Environmental Satellites (GOES) R-series Advanced Baseline Imager (ABI) and sister sensors as a research demonstration effort.
Steve’s working group participation included the Global Energy and Water Exchanges (GEWEX) Cloud Assessment Working Group (2008–present); the International Cloud Working Group (ICWG), which is part of the Coordination Group for Meteorological Satellites (CGMS), and its original incarnation, the Cloud Retrieval Evaluation Working (CREW) since 2009; and the NASA Observations for Modeling Intercomparison Studies (obs4MIPs) Working Group (2011–2013). Other notable roles included Deputy Chair of the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Science Definition Team (2011–2012) and membership in the Advanced Composition Explorer (ACE) Science Definition Team (2009–2011), the ABI Cloud Team (2005–2009), and the Climate Absolute Radiance and Refractivity Observatory (CLARREO) Mission Concept Team (2010-2011).
Steve has participated in numerous major airborne field campaigns over his career. His key ER-2 flight scientist and/or science team management roles included the Monterey Area Ship Track experiment (MAST,1994), First (International Satellite Cloud Climatology Project (ISCCP) Regional Experiment – Arctic Cloud Experiment [FIRE-ACE, 1998], Southern Africa Fire-Atmosphere Research Initiative (SAFARI-2000), Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL-FACE, 2002), and Tropical Composition, Cloud and Climate Coupling (TC4, 2007).
Supporting Earth Science Communications
Through his EOS Project Science Office role, Steve has been supportive of the activities of NASA’s Science Support Office (SSO) and personally participated in many NASA Science exhibits at both national and international scientific conferences, including serving as a Hyperwall presenter numerous times.
For The Earth Observer newsletter publication team in particular, Steve replaced Michael King as Acting EOS Senior Project Scientist in June 2008, taking over the authorship of “The Editor’s Corner” beginning with the May–June 2008 issue [Volume 20, Issue 3]. The Acting label was removed beginning with the January–February 2010 issue [Volume 22, Issue 1]. Steve has been a champion of continuing to retain a historical record of NASA science team meetings to maintain a chronology of advances made by different groups within the NASA Earth Science community. He was supportive of the Executive Editor’s efforts to create a series called “Perspectives on EOS,” which ran from 2008–2011 and told the stories of the early years of the EOS Program from the point of view of those who lived them. He also supported the development of articles to commemorate the 25th and 30th anniversary of The Earth Observer. Later, Steve helped guide the transition of the newsletter from a print publication – the November–December 2022 issue was the last printed issue – to fully online by July 2024, a few months after the publication’s 35th anniversary. The Earth Observer team will miss Steve’s keen insight, historical perspective, and encouragement that he has shown through his leadership for the past 85 issues of print and online publications.
A Career Recognized through Awards and Honors
Throughout his career, Steve has amassed numerous honors, including the Goddard William Nordberg Memorial Award for Earth Science in 2023 and the Verner E. Suomi Award from the American Meteorological Society (AMS) in 2016. He was named an AMS Fellow that same year. He received two NASA Agency Honor Awards – the Exceptional Achievement Medal in 2008 and the Exceptional Service Medal in 2015.
Steve received his bachelor’s degree and master’s degree in electrical engineering from Duke University and the University of California, Berkeley, respectively. He earned a Ph.D. in atmospheric sciences from the University of Arizona.
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By NASA
Explore Hubble Science Hubble Space Telescope NASA’s Hubble Uncovers Rare… 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 AI and Hubble Science Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations 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 5 min read
NASA’s Hubble Uncovers Rare White Dwarf Merger Remnant
This is an illustration of a white dwarf star merging into a red giant star. A bow shock forms as the dwarf plunges through the star’s outer atmosphere. The passage strips down the white dwarf’s outer layers, exposing an interior carbon core. Artwork: NASA, ESA, STScI, Ralf Crawford (STScI) An international team of astronomers has discovered a cosmic rarity: an ultra-massive white dwarf star resulting from a white dwarf merging with another star, rather than through the evolution of a single star. This discovery, made by NASA’s Hubble Space Telescope’s sensitive ultraviolet observations, suggests these rare white dwarfs may be more common than previously suspected.
“It’s a discovery that underlines things may be different from what they appear to us at first glance,” said the principal investigator of the Hubble program, Boris Gaensicke, of the University of Warwick in the United Kingdom. “Until now, this appeared as a normal white dwarf, but Hubble’s ultraviolet vision revealed that it had a very different history from what we would have guessed.”
A white dwarf is a dense object with the same diameter as Earth, and represents the end state for stars that are not massive enough to explode as core-collapse supernovae. Our Sun will become a white dwarf in about 5 billion years.
In theory, a white dwarf can have a mass of up to 1.4 times that of the Sun, but white dwarfs heavier than the Sun are rare. These objects, which astronomers call ultra-massive white dwarfs, can form either through the evolution of a single massive star or through the merger of a white dwarf with another star, such as a binary companion.
This new discovery, published in the journal Nature Astronomy, marks the first time that a white dwarf born from colliding stars has been identified by its ultraviolet spectrum. Prior to this study, six white dwarf merger products were discovered via carbon lines in their visible-light spectra. All seven of these are part of a larger group that were found to be bluer than expected for their masses and ages from a study with ESA’s Gaia mission in 2019, with the evidence of mergers providing new insights into their formation history.
Astronomers used Hubble’s Cosmic Origins Spectrograph to investigate a white dwarf called WD 0525+526. Located 128 light-years away, it is 20% more massive than the Sun. In visible light, the spectrum of WD 0525+526’s atmosphere resembled that of a typical white dwarf. However, Hubble’s ultraviolet spectrum revealed something unusual: evidence of carbon in the white dwarf’s atmosphere.
White dwarfs that form through the evolution of a single star have atmospheres composed of hydrogen and helium. The core of the white dwarf is typically composed mostly of carbon and oxygen or oxygen and neon, but a thick atmosphere usually prevents these elements from appearing in the white dwarf’s spectrum.
When carbon appears in the spectrum of a white dwarf, it can signal a more violent origin than the typical single-star scenario: the collision of two white dwarfs, or of a white dwarf and a subgiant star. Such a collision can burn away the hydrogen and helium atmospheres of the colliding stars, leaving behind a scant layer of hydrogen and helium around the merger remnant that allows carbon from the white dwarf’s core to float upward, where it can be detected.
WD 0525+526 is remarkable even within the small group of white dwarfs known to be the product of merging stars. With a temperature of almost 21,000 kelvins (37,000 degrees Fahrenheit) and a mass of 1.2 solar masses, WD 0525+526 is hotter and more massive than the other white dwarfs in this group.
WD 0525+526’s extreme temperature posed something of a mystery for the team. For cooler white dwarfs, such as the six previously discovered merger products, a process called convection can mix carbon into the thin hydrogen-helium atmosphere. WD 0525+526 is too hot for convection to take place, however. Instead, the team determined a more subtle process called semi-convection brings a small amount of carbon up into WD 0525+526’s atmosphere. WD 0525+526 has the smallest amount of atmospheric carbon of any white dwarf known to result from a merger, about 100,000 times less than other merger remnants.
The high temperature and low carbon abundance mean that identifying this white dwarf as the product of a merger would have been impossible without Hubble’s sensitivity to ultraviolet light. Spectral lines from elements heavier than helium, like carbon, become fainter at visible wavelengths for hotter white dwarfs, but these spectral signals remain bright in the ultraviolet, where Hubble is uniquely positioned to spot them.
“Hubble’s Cosmic Origins Spectrograph is the only instrument that can obtain the superb quality ultraviolet spectroscopy that was required to detect the carbon in the atmosphere of this white dwarf,” said study lead Snehalata Sahu from the University of Warwick.
Because WD 0525+526’s origin was revealed only once astronomers glimpsed its ultraviolet spectrum, it’s likely that other seemingly “normal” white dwarfs are actually the result of cosmic collisions — a possibility the team is excited to explore in the future.
“We would like to extend our research on this topic by exploring how common carbon white dwarfs are among similar white dwarfs, and how many stellar mergers are hiding among the normal white dwarf family,” said study co-leader Antoine Bedrad from the University of Warwick. “That will be an important contribution to our understanding of white dwarf binaries, and the pathways to supernova explosions.”
The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
To learn more about Hubble, visit: https://science.nasa.gov/hubble
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Related Images & Videos
White Dwarf Merger Illustration
This is an illustration of a white dwarf star merging into a red giant star. A bow shock forms as the dwarf plunges through the star’s outer atmosphere. The passage strips down the white dwarf’s outer layers, exposing an interior carbon core.
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Last Updated Aug 13, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Contact Media Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
Ray Villard
Space Telescope Science Institute
Baltimore, Maryland
Bethany Downer
ESA/Hubble
Garching, Germany
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Hubble Space Telescope Astrophysics Astrophysics Division Goddard Space Flight Center Stars The Universe White Dwarfs
Related Links and Documents
Science Paper: A hot white dwarf merger remnant revealed by an ultraviolet detection of carbon, PDF (23.45 MB)
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Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
Science: NASA, ESA, CXC, Yi-Chi Chang (National Tsing Hua University); Image Processing: Joseph DePasquale (STScI) NASA’s Hubble Space Telescope and NASA’s Chandra X-ray Observatory teamed up to identify a new possible example of a rare class of black holes, identified by X-ray emission (in purple) in this image released on July 24, 2025. Called NGC 6099 HLX-1, this bright X-ray source seems to reside in a compact star cluster in a giant elliptical galaxy. These rare black holes are called intermediate-mass black holes (IMBHs) and weigh between a few hundred to a few 100,000 times the mass of our Sun.
Learn more about IMBHs and what studying them can tell us about the universe.
Image credit: Science: NASA, ESA, CXC, Yi-Chi Chang (National Tsing Hua University); Image Processing: Joseph DePasquale (STScI)
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By European Space Agency
Image: A team of astronomers has taken the sharpest-ever picture of the unexpected interstellar comet 3I/ATLAS, using the crisp vision of the NASA/ESA Hubble Space Telescope.
ESA's Planetary Defence Office responded promptly to the discovery of the comet, and has been tracking it since the beginning of July.
Now, Hubble's observations from space are allowing astronomers to more accurately estimate the size of the comet’s solid icy nucleus. The upper limit on the diameter of the nucleus is 5.6 km, but it could be as small as 320 m across, researchers report.
Though the Hubble images put tighter constraints on the nucleus size compared to previous ground-based estimates, the solid heart of the comet presently cannot be directly seen, even by Hubble. Further observations, including by the NASA/ESA/CSA James Webb Space Telescope, will help refine our knowledge about the comet, including its chemical makeup.
Hubble also captured a dust plume ejected from the Sun-warmed side of the comet, and the hint of a dust tail streaming away from the nucleus. Hubble’s data show that the comet is losing dust in a similar manner to that from previously seen Sun-bound comets originating within our Solar System.
The big difference is that this interstellar visitor originated in some other stellar systems, elsewhere in our Milky Way galaxy.
3I/ATLAS is traveling through our Solar System at roughly 210 000 km per hour, the highest speed ever recorded for a Solar System visitor. This breathtaking sprint is evidence that the comet has been drifting through interstellar space for many billions of years. The gravitational slingshot effect from innumerable stars and nebulae the comet passed added momentum, ratcheting up its speed. The longer 3I/ATLAS was out in space, the higher its speed grew.
This comet was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on 1 July 2025 at a distance of 675 million km from the Sun. 3I/ATLAS should remain visible to ground-based telescopes until September, after which it will pass too close to the Sun to observe. It is expected to reappear on the other side of the Sun by early December.
Icy wanderers such as 3I/ATLAS offer a rare, tangible connection to the broader galaxy. To actually visit one would connect humankind with the Universe on a far greater scale. To this end, ESA is preparing the Comet Interceptor mission. The spacecraft will be launched in 2029 into a parking orbit, lying in wait for a suitable target – a pristine comet from the distant Oort Cloud that surrounds our Solar System, or, unlikely but highly appealing, an interstellar object.
While it is improbable that we will discover an interstellar object that is reachable for Comet Interceptor, as a first demonstration of a rapid response mission that waits in space for its target, it will be a pathfinder for possible future missions to intercept these mysterious visitors.
The research paper based on Hubble observations will be published in The Astrophysical Journal Letters.
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By NASA
A white-tailed deer fawn photographed on a Snapshot Wisconsin trail camera in Vernon County, WI Credit: WI DNR The Snapshot Wisconsin project recently collected their 100 millionth trail camera photo! What’s more, this milestone coincides with the project’s 10-year anniversary. Congratulations to the team and everyone who’s participated!
Snapshot Wisconsin utilizes a statewide network of volunteer-managed trail cameras to monitor and better understand the state’s diverse wildlife from white-tailed deer to snowshoe hares, whooping cranes, and much more.
“It’s been amazing to get a glimpse of our wild treasures via the Snapshot lens,” said one volunteer. “Satisfying to help advance wildlife research in the digital age.”
Snapshot Wisconsin was launched in 2013 with help from a NASA grant, and is overseen by the Wisconsin Department of Natural Resources. It recently won a new grant from NASA’s Citizen Science for Earth Systems Program.
Volunteer classifications of the species present in trail camera photos have fueled many different scientific investigations over the years. You, too, can get involved in the merriment by visiting the project’s site on the Zooniverse crowdsourcing platform and helping classify their latest photo season today!
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Last Updated Aug 06, 2025 Related Terms
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