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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
NASA The Moon’s light is refracted by Earth’s atmosphere in this April 13, 2025, photograph from the International Space Station as it orbited into a sunset 264 miles above the border between Bolivia and Brazil in South America.
Understanding the Moon helps us understand other planets, how they have evolved and the processes which have shaped their surfaces. It also helps us understand the influence the Moon has had on Earth, the record of the ancient Sun, and it serves as a platform to study the rest of the universe. By using the Moon as our closest testing ground for robotics and instrument systems, we can further human exploration to not only the Moon, but the rest of the solar system.
Through Artemis missions, NASA will send astronauts to explore the Moon for scientific discovery, economic benefits, and to build the foundation for the first crewed missions to Mars.
Image credit: NASA
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By European Space Agency
The exoplanet TRAPPIST-1 d intrigues astronomers looking for possibly habitable worlds beyond our solar system because it is similar in size to Earth, rocky, and resides in an area around its star where liquid water on its surface is theoretically possible. But according to a new study using data from the NASA/ESA/CSA James Webb Space Telescope, it does not have an Earth-like atmosphere.
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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 Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Webb’s First Images Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning Since July 2022, NASA’s James Webb Space Telescope has been unwaveringly focused on our universe. With its unprecedented power to detect and analyze otherwise invisible infrared light, Webb is making observations that were once impossible, changing our view of the cosmos from the most distant galaxies to our own solar system.
Webb was built with the promise of revolutionizing astronomy, of rewriting the textbooks. And by any measure, it has more than lived up to the hype — exceeding expectations to a degree that scientists had not dared imagine. Since science operations began, Webb has completed more than 860 scientific programs, with one-quarter of its time dedicated to imaging and three-quarters to spectroscopy. In just three years, it has collected nearly 550 terabytes of data, yielding more than 1,600 research papers, with intriguing results too numerous to list and a host of new questions to answer.
Here are just a few noteworthy examples.
1. The universe evolved significantly faster than we previously thought.
Webb was specifically designed to observe “cosmic dawn,” a time during the first billion years of the universe when the first stars and galaxies were forming. What we expected to see were a few faint galaxies, hints of what would become the galaxies we see nearby.
Instead, Webb has revealed surprisingly bright galaxies that developed within 300 million years of the big bang; galaxies with black holes that seem far too massive for their age; and an infant Milky Way-type galaxy that existed when the universe was just 600 million years old. Webb has observed galaxies that already “turned off” and stopped forming stars within a billion years of the big bang, as well as those that developed quickly into modern-looking “grand design” spirals within 1.5 billion years.
Hundreds of millions of years might not seem quick for a growth spurt, but keep in mind that the universe formed in the big bang roughly 13.8 billion years ago. If you were to cram all of cosmic time into one year, the most distant of these galaxies would have matured within the first couple of weeks, rapidly forming multiple generations of stars and enriching the universe with the elements we see today.
Image: JADES deep field
A near-infrared image from NASA’s James Webb Space Telescope shows a region known as the JADES Deep Field. Tens of thousands of galaxies are visible in this tiny patch of sky, including Little Red Dots and hundreds of galaxies that existed more than 13.2 billion years ago, when the universe was less than 600 million years old. Webb also spotted roughly 80 ancient supernovae, many of which exploded when the universe was less than 2 billion years old. This is ten times more supernovae than had ever been discovered before in the early universe. Comparing these supernovae from the distant past with those in the more recent, nearby universe helps us understand how stars in these early times formed, lived, and died, seeding space with the elements for new generations of stars and their planets. NASA, ESA, CSA, STScI, JADES Collaboration 2. Deep space is scattered with enigmatic “Little Red Dots.”
Webb has revealed a new type of galaxy: a distant population of mysteriously compact, bright, red galaxies dubbed Little Red Dots. What makes Little Red Dots so bright and so red? Are they lit up by dense groupings of unusually bright stars or by gas spiraling into a supermassive black hole, or both? And whatever happened to them? Little Red Dots seem to have appeared in the universe around 600 million years after the big bang (13.2 billion years ago), and rapidly declined in number less than a billion years later. Did they evolve into something else? If so, how? Webb is probing Little Red Dots in more detail to answer these questions.
3. Pulsating stars and a triply lensed supernova are further evidence that the “Hubble Tension” is real.
How fast is the universe expanding? It’s hard to say because different ways of calculating the current expansion rate yield different results — a dilemma known as the Hubble Tension. Are these differences just a result of measurement errors, or is there something weird going on in the universe? So far, Webb data indicates that the Hubble Tension is not caused by measurement errors. Webb was able to distinguish pulsating stars from nearby stars in a crowded field, ensuring that the measurements weren’t contaminated by extra light. Webb also discovered a distant, gravitationally lensed supernova whose image appears in three different locations and at three different times during its explosion. Calculating the expansion rate based on the brightness of the supernova at these three different times provides an independent check on measurements made using other techniques. Until the matter of the Hubble Tension is settled, Webb will continue measuring different objects and exploring new methods.
4. Webb has found surprisingly rich and varied atmospheres on gas giants orbiting distant stars.
While NASA’s Hubble Space Telescope made the first detection of gases in the atmosphere of a gas giant exoplanet (a planet outside our solar system), Webb has taken studies to an entirely new level. Webb has revealed a rich cocktail of chemicals, including hydrogen sulfide, ammonia, carbon dioxide, methane, and sulfur dioxide — none of which had been clearly detected in an atmosphere outside our solar system before. Webb has also been able to examine exotic climates of gas giants as never before, detecting flakes of silica “snow” in the skies of the puffy, searing-hot gas giant WASP-17 b, for example, and measuring differences in temperature and cloud cover between the permanent morning and evening skies of WASP-39 b.
Image: Spectrum of WASP-107 b
A transmission spectrum of the “warm Neptune” exoplanet WASP-107 b captured by NASA’s Hubble and Webb space telescopes, shows clear evidence for water, carbon dioxide, carbon monoxide, methane, sulfur dioxide, and ammonia in the planet’s atmosphere. These measurements allowed researchers to estimate the interior temperature and mass of the core of the planet, as well as understand the chemistry and dynamics of the atmosphere. NASA, ESA, CSA, Ralf Crawford (STScI) 5. A rocky planet 40 light-years from Earth may have an atmosphere fed by gas bubbling up from its lava-covered surface.
Detecting, let alone analyzing, a thin layer of gas surrounding a small rocky planet is no easy feat, but Webb’s extraordinary ability to measure extremely subtle changes in the brightness of infrared light makes it possible. So far, Webb has been able to rule out significant atmosphere on a number of rocky planets, and has found tantalizing signs of carbon monoxide or carbon dioxide on 55 Cancri e, a lava world that orbits a Sun-like star. With findings like these, Webb is laying the groundwork for NASA’s future Habitable Worlds Observatory, which will be the first mission purpose-built to directly image and search for life on Earth-like planets around Sun-like stars.
6. Webb exposes the skeletal structure of nearby spiral galaxies in mesmerizing detail.
We already knew that galaxies are collections of stars, planets, dust, gas, dark matter, and black holes: cosmic cities where stars form, live, die, and are recycled into the next generation. But we had never been able to see the structure of a galaxy and the interactions between stars and their environment in such detail. Webb’s infrared vision reveals filaments of dust that trace the spiral arms, old star clusters that make up galactic cores, newly forming stars still encased in dense cocoons of glowing dust and gas, and clusters of hot young stars carving enormous cavities in the dust. It also elucidates how stellar winds and explosions actively reshape their galactic homes.
Image: PHANGS Phantom Galaxy (M74/NGC 628)
A near- to mid-infrared image from NASA’s James Webb Space Telescope highlights details in the complex structure of a nearby galaxy that are invisible to other telescopes. The image of NGC 628, also known as the Phantom Galaxy, shows spiral arms with lanes of warm dust (represented in red), knots of glowing gas (orange-yellow), and giant bubbles (black) carved by hot, young stars. The dust-free core of the galaxy is filled with older, cooler stars (blue). NASA, ESA, CSA, STScI, Janice Lee (STScI), Thomas Williams (Oxford), PHANGS team 7. It can be hard to tell the difference between a brown dwarf and a rogue planet.
Brown dwarfs form like stars, but are not dense or hot enough to fuse hydrogen in their cores like stars do. Rogue planets form like other planets, but have been ejected from their system and no longer orbit a star. Webb has spotted hundreds of brown-dwarf-like objects in the Milky Way, and has even detected some candidates in a neighboring galaxy. But some of these objects are so small — just a few times the mass of Jupiter — that it is hard to figure out how they formed. Are they free-floating gas giant planets instead? What is the least amount of material needed to form a brown dwarf or a star? We’re not sure yet, but thanks to three years of Webb observations, we now know there is a continuum of objects from planets to brown dwarfs to stars.
8. Some planets might be able to survive the death of their star.
When a star like our Sun dies, it swells up to form a red giant large enough to engulf nearby planets. It then sheds its outer layers, leaving behind a super-hot core known as a white dwarf. Is there a safe distance that planets can survive this process? Webb might have found some planets orbiting white dwarfs. If these candidates are confirmed, it would mean that it is possible for planets to survive the death of their star, remaining in orbit around the slowly cooling stellar ember.
9. Saturn’s water supply is fed by a giant fountain of vapor spewing from Enceladus.
Among the icy “ocean worlds” of our solar system, Saturn’s moon Enceladus might be the most intriguing. NASA’s Cassini mission first detected water plumes coming out of its southern pole. But only Webb could reveal the plume’s true scale as a vast cloud spanning more than 6,000 miles, about 20 times wider than Enceladus itself. This water spreads out into a donut-shaped torus encircling Saturn beyond the rings that are visible in backyard telescopes. While a fraction of the water stays in that ring, the majority of it spreads throughout the Saturnian system, even raining down onto the planet itself. Webb’s unique observations of rings, auroras, clouds, winds, ices, gases, and other materials and phenomena in the solar system are helping us better understand what our cosmic neighborhood is made of and how it has changed over time.
Video: Water plume and torus from Enceladus
A combination of images and spectra captured by NASA’s James Webb Space Telescope show a giant plume of water jetting out from the south pole of Saturn’s moon Enceladus, creating a donut-shaped ring of water around the planet.
Credit: NASA, ESA, CSA, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI), L. Hustak (STScI) 10. Webb can size up asteroids that may be headed for Earth.
In 2024 astronomers discovered an asteroid that, based on preliminary calculations, had a chance of hitting Earth. Such potentially hazardous asteroids become an immediate focus of attention, and Webb was uniquely able to measure the object, which turned out to be the size of a 15-story building. While this particular asteroid is no longer considered a threat to Earth, the study demonstrated Webb’s ability to assess the hazard.
Webb also provided support for NASA’s Double Asteroid Redirection Test (DART) mission, which deliberately smashed into the Didymos binary asteroid system, showing that a planned impact could deflect an asteroid on a collision course with Earth. Both Webb and Hubble observed the impact, serving witness to the resulting spray of material that was ejected. Webb’s spectroscopic observations of the system confirmed that the composition of the asteroids is probably typical of those that could threaten Earth.
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In just three years of operations, Webb has brought the distant universe into focus, revealing unexpectedly bright and numerous galaxies. It has unveiled new stars in their dusty cocoons, remains of exploded stars, and skeletons of entire galaxies. It has studied weather on gas giants, and hunted for atmospheres on rocky planets. And it has provided new insights into the residents of our own solar system.
But this is only the beginning. Engineers estimate that Webb has enough fuel to continue observing for at least 20 more years, giving us the opportunity to answer additional questions, pursue new mysteries, and put together more pieces of the cosmic puzzle.
For example: What were the very first stars like? Did stars form differently in the early universe? Do we even know how galaxies form? How do stars, dust, and supermassive black holes affect each other? What can merging galaxy clusters tell us about the nature of dark matter? How do collisions, bursts of stellar radiation, and migration of icy pebbles affect planet-forming disks? Can atmospheres survive on rocky worlds orbiting active red dwarf stars? Is Uranus’s moon Ariel an ocean world?
As with any scientific endeavor, every answer raises more questions, and Webb has shown that its investigative power is unmatched. Demand for observing time on Webb is at an all-time high, greater than any other telescope in history, on the ground or in space. What new findings await?
By Dr. Macarena Garcia Marin and Margaret W. Carruthers, Space Telescope Science Institute, Baltimore, Maryland
Media Contacts
Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Christine Pulliam – cpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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Last Updated Jul 02, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
James Webb Space Telescope (JWST) Astrophysics Black Holes Brown Dwarfs Exoplanet Science Exoplanets Galaxies Galaxies, Stars, & Black Holes Goddard Space Flight Center Nebulae Science & Research Star-forming Nebulae Stars Studying Exoplanets The Universe View the full article
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By European Space Agency
The second of the Meteosat Third Generation (MTG) satellites and the first instrument for the Copernicus Sentinel-4 mission lifted off at 23:04 CEST on Tuesday, 1 July. The satellite is now on its way to monitor Earth’s atmosphere from an altitude of 36 000 km. From this geostationary orbit, the missions can provide game-changing data for forecasting severe storms and air pollution over Europe.
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