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By European Space Agency
Image: Part of the Gibson Desert in Western Australia is featured in this image, captured by the Φsat-2 mission in June 2025. View the full article
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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 Science James Webb Space Telescope (JWST) NASA Webb Looks at… 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 6 Min Read NASA Webb Looks at Earth-Sized, Habitable-Zone Exoplanet TRAPPIST-1 e
This artist’s concept shows the volatile red dwarf star TRAPPIST-1 and its four most closely orbiting planets. Full image and caption shown below. Credits:
Artwork: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI) Scientists are in the midst of observing the exoplanet TRAPPIST-1 e with NASA’s James Webb Space Telescope. Careful analysis of the results so far presents several potential scenarios for what the planet’s atmosphere and surface may be like, as NASA science missions lay key groundwork to answer the question, “are we alone in the universe?”
“Webb’s infrared instruments are giving us more detail than we’ve ever had access to before, and the initial four observations we’ve been able to make of planet e are showing us what we will have to work with when the rest of the information comes in,” said Néstor Espinoza of the Space Telescope Science Institute in Baltimore, Maryland, a principal investigator on the research team. Two scientific papers detailing the team’s initial results are published in the Astrophysical Journal Letters.
Image A: Trappist-1 e (Artist’s Concept)
This artist’s concept shows the volatile red dwarf star TRAPPIST-1 and its four most closely orbiting planets, all of which have been observed by NASA’s James Webb Space Telescope. Webb has found no definitive signs of an atmosphere around any of these worlds yet. Artwork: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI) Of the seven Earth-sized worlds orbiting the red dwarf star TRAPPIST-1, planet e is of particular interest because it orbits the star at a distance where water on the surface is theoretically possible — not too hot, not too cold — but only if the planet has an atmosphere. That’s where Webb comes in. Researchers aimed the telescope’s powerful NIRSpec (Near-Infrared Spectrograph) instrument at the system as planet e transited, or passed in front of, its star. Starlight passing through the planet’s atmosphere, if there is one, will be partially absorbed, and the corresponding dips in the light spectrum that reaches Webb will tell astronomers what chemicals are found there. With each additional transit, the atmospheric contents become clearer as more data is collected.
Primary atmosphere unlikely
Though multiple possibilities remain open for planet e because only four transits have been analyzed so far, the researchers feel confident that the planet does not still have its primary, or original, atmosphere. TRAPPIST-1 is a very active star, with frequent flares, so it is not surprising to researchers that any hydrogen-helium atmosphere with which the planet may have formed would have been stripped off by stellar radiation. However many planets, including Earth, build up a heavier secondary atmosphere after losing their primary atmosphere. It is possible that planet e was never able to do this and does not have a secondary atmosphere. Yet researchers say there is an equal chance there is an atmosphere, and the team developed novel approaches to working with Webb’s data to determine planet e’s potential atmospheres and surface environments.
World of (fewer) possibilities
The researchers say it is unlikely that the atmosphere of TRAPPIST-1 e is dominated by carbon dioxide, analogous to the thick atmosphere of Venus and the thin atmosphere of Mars. However, the researchers also are careful to note that there are no direct parallels with our solar system.
“TRAPPIST-1 is a very different star from our Sun, and so the planetary system around it is also very different, which challenges both our observational and theoretical assumptions,” said team member Nikole Lewis, an associate professor of astronomy at Cornell University.
If there is liquid water on TRAPPIST-1 e, the researchers say it would be accompanied by a greenhouse effect, in which various gases, particularly carbon dioxide, keep the atmosphere stable and the planet warm.
“A little greenhouse effect goes a long way,” said Lewis, and the measurements do not rule out adequate carbon dioxide to sustain some water on the surface. According to the team’s analysis, the water could take the form of a global ocean, or cover a smaller area of the planet where the star is at perpetual noon, surrounded by ice. This would be possible because, due to the TRAPPIST-1 planets’ sizes and close orbits to their star, it is thought that they all are tidally locked, with one side always facing the star and one side always in darkness.
Image B: TRAPPIST-1 e Transmission Spectrum (NIRSpec)
This graphic compares data collected by Webb’s NIRSpec (Near-Infrared Spectrograph) with computer models of exoplanet TRAPPIST-1 e with (blue) and without (orange) an atmosphere. Narrow colored bands show the most likely locations of data points for each model. Illustration: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI) Innovative new method
Espinoza and co-principal investigator Natalie Allen of Johns Hopkins University are leading a team that is currently making 15 additional observations of planet e, with an innovative twist. The scientists are timing the observations so that Webb catches both planets b and e transiting the star one right after the other. After previous Webb observations of planet b, the planet orbiting closest to TRAPPIST-1, scientists are fairly confident it is a bare rock without an atmosphere. This means that signals detected during planet b’s transit can be attributed to the star only, and because planet e transits at nearly the same time, there will be less complication from the star’s variability. Scientists plan to compare the data from both planets, and any indications of chemicals that show up only in planet e’s spectrum can be attributed to its atmosphere.
“We are really still in the early stages of learning what kind of amazing science we can do with Webb. It’s incredible to measure the details of starlight around Earth-sized planets 40 light-years away and learn what it might be like there, if life could be possible there,” said Ana Glidden, a post-doctoral researcher at Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, who led the research on possible atmospheres for planet e. “We’re in a new age of exploration that’s very exciting to be a part of,” she said.
The four transits of TRAPPIST-1 e analyzed in the new papers published today were collected by the JWST Telescope Scientist Team’s DREAMS (Deep Reconnaissance of Exoplanet Atmospheres using Multi-instrument Spectroscopy) collaboration.
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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Trappist-1 e (Artist’s Concept)
This artist’s concept shows the volatile red dwarf star TRAPPIST-1 and its four most closely orbiting planets, all of which have been observed by NASA’s James Webb Space Telescope. Webb has found no definitive signs of an atmosphere around any of these worlds yet.
TRAPPIST-1 e Transmission Spectrum (NIRSpec)
This graphic compares data collected by Webb’s NIRSpec (Near-Infrared Spectrograph) with computer models of exoplanet TRAPPIST-1 e with (blue) and without (orange) an atmosphere. Narrow colored bands show the most likely locations of data points for each model.
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Last Updated Sep 08, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Location NASA Goddard Space Flight Center Contact Media Laura Betz
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
laura.e.betz@nasa.gov
Leah Ramsay
Space Telescope Science Institute
Baltimore, Maryland
Hannah Braun
Space Telescope Science Institute
Baltimore, Maryland
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By NASA
Advancing Single-Photon Sensing Image Sensors to Enable the Search for Life Beyond Earth
A NASA-sponsored team is advancing single-photon sensing Complementary Metal-Oxide-Semiconductor (CMOS) detector technology that will enable future NASA astrophysics space missions to search for life on other planets. As part of their detector maturation program, the team is characterizing sensors before, during, and after high-energy radiation exposure; developing novel readout modes to mitigate radiation-induced damage; and simulating a near-infrared CMOS pixel prototype capable of detecting individual photons.
Single-photon sensing and photon-number resolving CMOS image sensors: a 9.4 Mpixel sensor (left) and a 16.7 Mpixel sensor (right). Credit: CfD, RIT Are we alone in the universe? This age-old question has inspired scientific exploration for centuries. If life on other planets evolves similarly to life on Earth, it can imprint its presence in atmospheric spectral features known asbiosignatures. They include absorption and emission lines in the spectrum produced by oxygen, carbon dioxide, methane, and other molecules that could indicate conditions which can support life. A future NASA astrophysics mission, the Habitable Worlds Observatory (HWO), will seek to find biosignatures in the ultraviolet, optical, and near-infrared (NIR) spectra of exoplanet atmospheres to look for evidence that life may exist elsewhere in the universe.
HWO will need highly sensitive detector technology to detect these faint biosignatures on distant exoplanets. The Single-Photon Sensing Complementary Metal-Oxide-Semiconductor (SPSCMOS) image sensor is a promising technology for this application. These silicon-based sensors can detect and resolve individual optical-wavelength photons using a low-capacitance, high-gain floating diffusion sense node. They operate effectively over a broad temperature range, including at room temperature. They have near-zero read noise, are tolerant to radiation, and generate very little unwanted signal—such as dark current. When cooled to 250 K, the dark current drops to just one electron every half-hour. If either the read noise or dark current is too high, the sensor will fail to detect the faint signals that biosignatures produce.
A research team at the Rochester Institute of Technology (RIT) Center for Detectors (CfD) is accelerating the readiness of these SPSCMOS sensors for use in space missions through detector technology maturation programs funded by NASA’s Strategic Astrophysics Technology and Early Stage Innovations solicitations. These development programs include several key goals:
Characterize critical detector performance metrics like dark current, quantum efficiency, and read noise before, during, and after exposure to high-energy radiation Develop new readout modes for these sensors to mitigate effects from short-term and long-term radiation damage Design a new NIR version of the sensor using Technology Computer-Aided Design (TCAD) software SPSCMOS sensors operate similarly to traditional CMOS image sensors but are optimized to detect individual photons—an essential capability for ultra-sensitive space-based observations, such as measuring the gases in the atmospheres of exoplanets. Incoming photons enter the sensor and generate free charges (electrons) in the sensor material. These charges collect in a pixel’s storage well and eventually transfer to a low-capacitance component called the floating diffusion (FD) sense node where each free charge causes a large and resolved voltage shift. This voltage shift is then digitized to read the signal.
Experiments that measure sensor performance in a space relevant environment use a vacuum Dewar and a thermally-controlled mount to allow precise tuning of the sensors temperature. The Dewar enables testing at conditions that match the expected thermal environment of the HWO instrument, and can even cool the sensor and its on-chip circuits to temperatures colder than any prior testing reported for this detector family. These tests are critical for revealing performance limitations with respect to detector metrics like dark current, quantum efficiency, and read noise. As temperatures change, the electrical properties of on-chip circuits can also change, which affects the read out of charge in a pixel.
The two figures show results for SPSCMOS devices. The figure on the left shows a photon counting histogram with peaks that correspond to photon number. The figure on the right shows the dark current for a SPSCMOS device before and after exposure to 50 krad of 60 MeV protons. Credit: CfD, RIT The radiation-rich environment for HWO will cause temporary and permanent effects in the sensor. These effects can corrupt the signal measured in a pixel, interrupt sensor clocking and digital logic, and can cause cumulative damage that gradually degrades sensor performance. To mitigate the loss of detector sensitivity throughout a mission lifetime, the RIT team is developing new readout modes that are not available in commercial CMOS sensors. These custom modes sample the signal over time (a “ramp” acquisition) to enable the detection and removal of cosmic ray artifacts. In one mode, when the system identifies an artifact, it segments the signal ramp and selectively averages the segments to reconstruct the original signal—preserving scientific data that would otherwise be lost. In addition, a real-time data acquisition system monitors the detector’s power consumption, which may change from the accumulation of damage throughout a mission. The acquisition system records these shifts and communicates with the detector electronics to adjust voltages and maintain nominal operation. These radiation damage mitigation strategies will be evaluated during a number of test programs at ground-based radiation facilities. The tests will help identify unique failure mechanisms that impact SPSCMOS technology when it is exposed to radiation equivalent to the dose expected for HWO.
Custom acquisition electronics (left) that will control the sensors during radiation tests, and an image captured using this system (right). Credit: CfD, RIT While existing SPSCMOS sensors are limited to detecting visible light due to their silicon-based design, the RIT team is developing the world’s first NIR single-photon photodiode based on the architecture used in the optical sensors. The photodiode design starts as a simulation in TCAD software to model the optical and electrical properties of the low-capacitance CMOS architecture. The model simulates light-sensitive circuits using both silicon and Mercury Cadmium Telluride (HgCdTe or MCT) material to determine how well the pixel would measure photo-generated charge if a semiconductor foundry physically fabricated it. It has 2D and 3D device structures that convert light into electrical charge, and circuits to control charge transfer and signal readout with virtual probes that can measure current flow and electric potential. These simulations help to evaluate the key mechanisms like the conversion of light into electrons, storing and transferring the electrons, and the output voltage of the photodiode sampling circuit.
In addition to laboratory testing, the project includes performance evaluations at a ground-based telescope. These tests allow the sensor to observe astronomical targets that cannot be fully replicated in lab. Star fields and diffuse nebulae challenge the detector’s full signal chain under real sky backgrounds with faint flux levels, field-dependent aberrations, and varying seeing conditions. These observations help identify performance limitations that may not be apparent in controlled laboratory measurements.
In January 2025, a team of researchers led by PhD student Edwin Alexani used an SPSCMOS-based camera at the C.E.K. Mees Observatory in Ontario County, New York. They observed star cluster M36 to evaluate the sensor’s photometric precision, and the Bubble Nebula in a narrow-band H-alpha filter. The measured dark current and read noise were consistent with laboratory results.
The team observed photometric reference stars to estimate the quantum efficiency (QE) or the ability for the detector to convert photons into signal. The calculated QE agreed with laboratory measurements, despite differences in calibration methods.
The team also observed the satellite STARLINK-32727 as it passed through the telescope’s field of view and measured negligible persistent charge—residual signal that can remain in detector pixels after exposure to a bright source. Although the satellite briefly produced a bright streak across several pixels due to reflected sunlight, the average latent charge in affected pixels was only 0.03 e–/pix – well below both the sky-background and sensor’s read noise.
Images captured at the C.E.K. Mees Observatory. Left: The color image shows M36 in the Johnson color filters B (blue), V (green), and R (red) bands (left). Right: Edwin Alexani and the SPSCMOS camera (right). Credit: : CfD, RIT As NASA advances and matures the HWO mission, SPSCMOS technology promises to be a game-changer for exoplanet and general astrophysics research. These sensors will enhance our ability to detect and analyze distant worlds, bringing us one step closer to answering one of humanity’s most profound questions: are we alone?
For additional details, see the entry for this project on NASA TechPort.
Project Lead(s): Dr. Donald F. Figer, Future Photon Initiative and Center for Detectors, Rochester Institute of Technology (RIT), supported by engineer Justin Gallagher and a team of students.
Sponsoring Organization(s): NASA Astrophysics Division, Strategic Astrophysics Technology (SAT) Program and NASA Space Technology Mission Directorate (STMD), Early Stage Innovations (ESI) Program
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Last Updated Sep 02, 2025 Related Terms
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