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Astronomers Discover an Infrared Background Glow in the Universe
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By NASA
Research Astrophysicist and Roman’s Deputy Wide Field Instrument Scientist – Goddard Space Flight Center
From a young age, Ami Choi — now a research astrophysicist at NASA — was drawn to the vast and mysterious. By the fifth grade, she had narrowed her sights to two career paths: marine biology or astrophysics.
“I’ve always been interested in exploring big unknown realms, and things that aren’t quite tangible,” Choi said. That curiosity has served her all throughout her career.
In addition to conducting research, Ami Choi shares science with the public at various outreach events, including tours at NASA’s Goddard Space Flight Center in Greenbelt, Md. This photo captures one tour stop, outside the largest clean room at Goddard.Credit: NASA/Travis Wohlrab As a student at University Laboratory High School in Urbana, Illinois, Choi gravitated toward astrophysics and was fascinated by things like black holes. She studied physics as an undergraduate at the University of Chicago, though she says math and physics didn’t necessarily come easily to her.
“I wasn’t very good at it initially, but I really liked the challenge so I stuck with it,” Choi said.
Early opportunities to do research played a pivotal role in guiding her career. As an undergraduate, Choi worked on everything from interacting galaxies to the stuff in between stars in our galaxy, called the interstellar medium. She learned how to code, interpret data, and do spectroscopy, which involves splitting light from cosmic objects into a rainbow of colors to learn about things like their composition.
After college, Choi read an article about physicist Janet Conrad’s neutrino work at Fermilab and was so inspired by Conrad’s enthusiasm and inclusivity that she cold-emailed her to see if there were any positions available in her group.
On October 14, 2023, Ami took a break from a thermal vacuum shift to snap a selfie with a partial eclipse. She was visiting BAE, Inc. in Boulder, Co., where the primary instrument for NASA’s Nancy Grace Roman Space Telescope was undergoing testing. Credit: Courtesy of Ami Choi “That one email led to a year at Fermilab working on neutrino physics,” Choi said.
She went on to earn a doctorate at the University of California, Davis, where she studied weak gravitational lensing — the subtle warping of light by gravity — and used it to explore dark matter, dark energy, and the large-scale structure of the universe.
Her postdoctoral work took Choi first to the University of Edinburgh in Scotland, where she contributed to the Kilo-Degree Survey, and later to The Ohio State University, where she became deeply involved in DES (the Dark Energy Survey) and helped lay the groundwork for the Nancy Grace Roman Space Telescope — NASA’s next flagship astrophysics mission.
“One of my proudest moments came in 2021, when the DES released its third-year cosmology results,” Choi said. “It was a massive team effort conducted during a global pandemic, and I had helped lead as a co-convener of the weak lensing team.”
Choi regularly presents information about NASA’s Nancy Grace Roman Space Telescope to fellow scientists and the public. Here, she gives a Hyperwall talk at an AAS (American Astronomical Society) meeting.Credit: Courtesy of Ami Choi After a one-year stint at the California Institute of Technology in Pasadena, where Choi worked on SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer)—an observatory that’s surveying stars and galaxies—she became a research astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. She also serves as the deputy Wide Field Instrument scientist for Roman. Choi operates at the intersection of engineering, calibration, and cosmology, helping translate ground-based testing into flight-ready components that will help Roman reveal large swaths of the universe in high resolution.
“I’m very excited for Roman’s commissioning phase — the first 90 days when the spacecraft will begin transmitting data from orbit,” Choi said.
Choi, photographed here in Death Valley, finds joy in the natural world outside of work. She cycles, hikes, and tends a small vegetable garden with a friend from grad school. Credit: Insook Choi (used with permission) She’s especially drawn to so-called systematics, which are effects that can alter the signals scientists are trying to measure. “People sometimes think of systematics as nuisances, but they’re often telling us something deeply interesting about either the physics of something like a detector or the universe itself,” Choi said. “There’s always something more going on under the surface.”
While she’s eager to learn more about things like dark energy, Choi is also looking forward to seeing all the other ways our understanding of the universe grows. “It’s more than just an end goal,” she said. “It’s about everything we learn along the way. Every challenge we overcome, every detail we uncover, is an important discovery too.”
For those who hope to follow a similar path, Choi encourages staying curious, being persistent, and taking opportunities to get involved in research. And don’t let the tricky subjects scare you away! “You don’t have to be perfect at math or physics right away,” she said. “What matters most is a deep curiosity and the tenacity to keep pushing through.”
By Ashley Balzer
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Sep 09, 2025 EditorAshley BalzerLocationGoddard Space Flight Center Related Terms
Goddard Space Flight Center Nancy Grace Roman Space Telescope People of Goddard View the full article
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By NASA
5 min read
Astronomers Map Stellar ‘Polka Dots’ Using NASA’s TESS, Kepler
Scientists have devised a new method for mapping the spottiness of distant stars by using observations from NASA missions of orbiting planets crossing their stars’ faces. The model builds on a technique researchers have used for decades to study star spots.
By improving astronomers’ understanding of spotty stars, the new model — called StarryStarryProcess — can help discover more about planetary atmospheres and potential habitability using data from telescopes like NASA’s upcoming Pandora mission.
“Many of the models researchers use to analyze data from exoplanets, or worlds beyond our solar system, assume that stars are uniformly bright disks,” said Sabina Sagynbayeva, a graduate student at Stony Brook University in New York. “But we know just by looking at our own Sun that stars are more complicated than that. Modeling complexity can be difficult, but our approach gives astronomers an idea of how many spots a star might have, where they are located, and how bright or dark they are.”
A paper describing StarryStarryProcess, led by Sagynbayeva, published Monday, August 25, in The Astrophysical Journal.
Watch to learn how a new tool uses data from exoplanets, worlds beyond our solar system, to tell us about their polka-dotted stars.
NASA’s Goddard Space Flight Center
Download images and videos through NASA’s Scientific Visualization Studio.
NASA’s TESS (Transiting Exoplanet Survey Satellite) and now-retired Kepler Space Telescope were designed to identify planets using transits, dips in stellar brightness caused when a planet passes in front of its star.
These measurements reveal how the star’s light varies with time during each transit, and astronomers can arrange them in a plot astronomers call a light curve. Typically, a transit light curve traces a smooth sweep down as the planet starts passing in front of the star’s face. It reaches a minimum brightness when the world is fully in front of the star and then rises smoothly as the planet exits and the transit ends.
By measuring the time between transits, scientists can determine how far the planet lies from its star and estimate its surface temperature. The amount of missing light from the star during a transit can reveal the planet’s size, which can hint at its composition.
Every now and then, though, a planet’s light curve appears more complicated, with smaller dips and peaks added to the main arc. Scientists think these represent dark surface features akin to sunspots seen on our own Sun — star spots.
The Sun’s total number of sunspots varies as it goes through its 11-year solar cycle. Scientists use them to determine and predict the progress of that cycle as well as outbreaks of solar activity that could affect us here on Earth.
Similarly, star spots are cool, dark, temporary patches on a stellar surface whose sizes and numbers change over time. Their variability impacts what astronomers can learn about transiting planets.
Scientists have previously analyzed transit light curves from exoplanets and their host stars to look at the smaller dips and peaks. This helps determine the host star’s properties, such as its overall level of spottiness, inclination angle of the planet’s orbit, the tilt of the star’s spin compared to our line of sight, and other factors. Sagynbayeva’s model uses light curves that include not only transit information, but also the rotation of the star itself to provide even more detailed information about these stellar properties.
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This artist’s concept illustrates the varying brightness of star with a transiting planet and several star spots. NASA’s Goddard Space Flight Center “Knowing more about the star in turn helps us learn even more about the planet, like a feedback loop,” said co-author Brett Morris, a senior software engineer at the Space Telescope Science Institute in Baltimore. “For example, at cool enough temperatures, stars can have water vapor in their atmospheres. If we want to look for water in the atmospheres of planets around those stars — a key indicator of habitability — we better be very sure that we’re not confusing the two.”
To test their model, Sagynbayeva and her team looked at transits from a planet called TOI 3884 b, located around 141 light-years away in the northern constellation Virgo.
Discovered by TESS in 2022, astronomers think the planet is a gas giant about five times bigger than Earth and 32 times its mass.
The StarryStarryProcess analysis suggests that the planet’s cool, dim star — called TOI 3384 — has concentrations of spots at its north pole, which also tips toward Earth so that the planet passes over the pole from our perspective.
Currently, the only available data sets that can be fit by Sagynbayeva’s model are in visible light, which excludes infrared observations taken by NASA’s James Webb Space Telescope. But NASA’s upcoming Pandora mission will benefit from tools like this one. Pandora, a small satellite developed through NASA’s Astrophysics Pioneers Program, will study the atmospheres of exoplanets and the activity of their host stars with long-duration multiwavelength observations. The Pandora mission’s goal is to determine how the properties of a star’s light differs when it passes through a planet’s atmosphere so scientists can better measure those atmospheres using Webb and other missions.
“The TESS satellite has discovered thousands of planets since it launched in 2018,” said Allison Youngblood, TESS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “While Pandora will study about 20 worlds, it will advance our ability to pick out which signals come from stars and which come from planets. The more we understand the individual parts of a planetary system, the better we understand the whole — and our own.”
Facebook logo @NASAUniverse @NASAUniverse Instagram logo @NASAUniverse By Jeanette Kazmierczak
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Media Contact:
Alise Fisher
202-358-2546
alise.m.fisher@nasa.gov
NASA Headquarters, Washington
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Last Updated Aug 25, 2025 Related Terms
Astrophysics Exoplanet Atmosphere Exoplanets Galaxies, Stars, & Black Holes Galaxies, Stars, & Black Holes Research Goddard Space Flight Center Kepler / K2 Stars TESS (Transiting Exoplanet Survey Satellite) The Universe View the full article
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By NASA
KEY POINTS
Jupiter, Saturn, and Neptune each emit more energy than they receive from the Sun, meaning they have comparatively warm interiors. NASA’s Uranus flyby with Voyager 2 in 1986 found the planet colder than expected, which challenged ideas of how planets formed and evolved. However, with advanced computer modeling and a new look at old data, scientists think the planet may actually be warmer than previously expected. For millennia, astronomers thought Uranus was no more than a distant star. It wasn’t until the late 18th century that Uranus was universally accepted as a planet. To this day, the ringed, blue world subverts scientists’ expectations, but new NASA research helps puzzle out some of the world’s mystique.
This zoomed-in image of Uranus, captured by the Near-Infrared Camera on NASA’s James Webb Space Telescope on Feb. 6, 2023, reveals stunning views of Uranus’ rings. Credits: NASA, ESA, CSA, STScI Uranus is unlike any other planet in our solar system. It spins on its side, which means each pole directly faces the Sun for a continuous 42-year “summer.” Uranus also rotates in the opposite direction of all planets except Venus. Data from NASA’s Voyager 2 Uranus flyby in 1986 also suggested the planet is unusually cold inside, challenging scientists to reconsider fundamental theories of how planets formed and evolved throughout our solar system.
“Since Voyager 2’s flyby, everybody has said Uranus has no internal heat,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But it’s been really hard to explain why that is, especially when compared with the other giant planets.”
These Uranus projections came from only one up-close measurement of the planet’s emitted heat made by Voyager 2: “Everything hinges on that one data point,” said Simon. “That is part of the problem.”
Now, using an advanced computer modeling technique and revisiting decades of data, Simon and a team of scientists have found that Uranus does in fact generate some heat, as they reported on May 16 in the Monthly Notices of the Royal Astronomical Society journal.
A planet’s internal heat can be calculated by comparing the amount of energy it receives from the Sun to the amount it of energy it releases into space in the form of reflected light and emitted heat. The solar system’s other giant planets — Saturn, Jupiter, and Neptune — emit more heat than they receive, which means the extra heat is coming from inside, much of it left over from the high-energy processes that formed the planets 4.5 billion years ago. The amount of heat a planet exudes could be an indication of its age: the less heat released relative to the heat absorbed from the Sun, the older the planet is.
Uranus stood out from the other planets because it appeared to give off as much heat as it received, implying it had none of its own. This puzzled scientists. Some hypothesized that perhaps the planet is much older than all the others and has cooled off completely. Others proposed that a giant collision — the same one that may have knocked the planet on its side — blasted out all of Uranus’ heat. But none of these hypotheses satisfied scientists, motivating them to solve Uranus’ cold case.
“We thought, ‘Could it really be that there is no internal heat at Uranus?’” said Patrick Irwin, the paper’s lead author and professor of planetary physics at the University of Oxford in England. “We did many calculations to see how much sunshine is reflected by Uranus and we realized that it is actually more reflective than people had estimated.”
The researchers set out to determine Uranus’ full energy budget: how much energy it receives from the Sun compared to how much it reflects as sunlight and how much it emits as heat. To do this, they needed to estimate the total amount of light reflected from the planet at all angles. “You need to see the light that’s scattered off to the sides, not just coming straight back at you,” Simon said.
To get the most accurate estimate of Uranus’ energy budget yet, Oxford researchers developed a computer model that brought together everything known about Uranus’ atmosphere from decades of observations from ground- and space-based telescopes, including NASA’s Hubble Space Telescope and NASA’s Infrared Telescope Facility in Hawaii. The model included information about the planet’s hazes, clouds, and seasonal changes, all of which affect how sunlight is reflected and how heat escapes.
These side-by-side images of Uranus, taken eight years apart by NASA’s Hubble Space Telescope, show seasonal changes in the planet’s reflectivity. The left image shows the planet seven years after its northern spring equinox when the Sun was shining just above its equator. The second photo, taken six years before the planet’s summer solstice, portrays a bright and large northern polar cap. Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI) The researchers found that Uranus releases about 15% more energy than it receives from the Sun, a figure that is similar to another recent estimate from a separate study funded in part by NASA that was published July 14 in Geophysical Research Letters. These studies suggest Uranus it has its own heat, though still far less than its neighbor Neptune, which emits more than twice the energy it receives.
“Now we have to understand what that remnant amount of heat at Uranus means, as well as get better measurements of it,” Simon said.
Unraveling Uranus’ past is useful not only for mapping the timeline of when solar system planets formed and migrated to their current orbits, but it also helps scientists better understand many of the planets discovered outside the solar system, called exoplanets, a majority of which are the same size as Uranus.
By Emma Friedman
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Jul 17, 2025 Editor Lonnie Shekhtman Contact Lonnie Shekhtman lonnie.shekhtman@nasa.gov Location NASA Goddard Space Flight Center Related Terms
Planetary Science Planets The Solar System Uranus View the full article
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By European Space Agency
Astronomers have discovered a huge filament of hot gas bridging four galaxy clusters. At 10 times as massive as our galaxy, the thread could contain some of the Universe’s ‘missing’ matter, addressing a decades-long mystery.
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