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By NASA
5 min read
Ultra-low-noise Infrared Detectors for Exoplanet Imaging
A linear-mode avalanche photodiode array in the test dewar. The detector is the dark square in the center. Michael Bottom, University of Hawai’i One of the ultimate goals in astrophysics is the discovery of Earth-like planets that are capable of hosting life. While thousands of planets have been discovered around other stars, the vast majority of these detections have been made via indirect methods, that is, by detecting the effect of the planet on the star’s light, rather than detecting the planet’s light directly. For example, when a planet passes in front of its host star, the brightness of the star decreases slightly.
However, indirect methods do not allow for characterization of the planet itself, including its temperature, pressure, gravity, and atmospheric composition. Planetary atmospheres may include “biosignature” gases like oxygen, water vapor, carbon dioxide, etc., which are known to be key ingredients needed to support life as we know it. As such, direct imaging of a planet and characterization of its atmosphere are key to understanding its potential habitability.
But the technical challenges involved in imaging Earth-like extrasolar planets are extreme. First such planets are detected only by observing light they reflect from their parent star, and so they typically appear fainter than the stars they orbit by factors of about 10 billion. Furthermore, at the cosmic distances involved, the planets appear right next to the stars. A popular expression is that exoplanet imaging is like trying to detect a firefly three feet from a searchlight from a distance of 300 miles.
Tremendous effort has gone into developing starlight suppression technologies to block the bright glare of the star, but detecting the light of the planet is challenging in its own right, as planets are incredibly faint. One way to quantify the faintness of planetary light is to understand the photon flux rate. A photon is an indivisible particle of light, that is, the minimum detectable amount of light. On a sunny day, approximately 10 thousand trillion photons enter your eye every second. The rate of photons entering your eye from an Earth-like exoplanet around a nearby star would be around 10 to 100 per year. Telescopes with large mirrors can help collect as much of this light as possible, but ultra-sensitive detectors are also needed, particularly for infrared light, where the biosignature gases have their strongest effects. Unfortunately, state-of-the-art infrared detectors are far too noisy to detect the low level of light emitted from exoplanets.
With support from NASA’s Astrophysics Division and industrial partners, researchers at the University of Hawai’i are developing a promising detector technology to meet these stringent sensitivity requirements. These detectors, known as avalanche photodiode arrays, are constructed out of the same semiconductor material as conventional infrared sensors. However, these new sensors employ an extra “avalanche” layer that takes the signal from a single photon and multiplies it, much like an avalanche can start with a single snowball and quickly grow it to the size of a boulder. This signal amplification occurs before any noise from the detector is introduced, so the effective noise is proportionally reduced. However, at high avalanche levels, photodiodes start to behave badly, with noise exponentially increasing, which negates any benefits of the signal amplification. Late University of Hawai’i faculty member Donald Hall, who was a key figure in driving technology for infrared astronomy, realized the potential use of avalanche photodiodes for ultra-low-noise infrared astronomy with some modifications to the material properties.
University of Hawai’i team members with cryogenic dewar used to test the sensors. From left to right, Angelu Ramos, Michael Bottom, Shane Jacobson, Charles-Antoine Claveau. Michael Bottom, University of Hawai’i The most recent sensors benefit from a new design including a graded semiconductor bandgap that allows for excellent noise performance at moderate amplification, a mesa pixel geometry to reduce electronic crosstalk, and a read-out integrated circuit to allow for short readout times. “It was actually challenging figuring out just how sensitive these detectors are,” said Michael Bottom, associate professor at the University of Hawai’i and lead of development effort. “Our ‘light-tight’ test chamber, which was designed to evaluate the infrared sensors on the James Webb Space Telescope, was supposed to be completely dark. But when we put these avalanche photodiodes in the chamber, we started seeing light leaks at the level of a photon an hour, which you would never be able to detect using the previous generation of sensors.”
The new designs have a format of one megapixel, more than ten times larger than the previous iteration of sensors, and circuitry that allows for tracking and subtracting any electronic drifts. Additionally, the pixel size and control electronics are such that these new sensors could be drop-in replacements for the most common infrared sensors used on the ground, which would give new capabilities to existing instruments.
Image of the Palomar-2 globular cluster located in the constellation of Auriga, taken with the linear-mode avalanche photodiode arrays, taken from the first on-sky testing of the sensors using the University of Hawai’i’s 2.2 meter telescope. Michael Bottom, University of Hawai’i Last year, the team took the first on-sky images from the detectors, using the University of Hawai’i’s 2.2-meter telescope. “It was impressive to see the avalanche process on sky. When we turned up the gain, we could see more stars appear,” said Guillaume Huber, a graduate student working on the project. “The on-sky demonstration was important to prove the detectors could perform well in an operational environment,” added Michael Bottom.
According to the research team, while the current sensors are a major step forward, the megapixel format is still too small for many science applications, particularly those involving spectroscopy. Further tasks include improving detector uniformity and decreasing persistence. The next generation of sensors will be four times larger, meeting the size requirements for the Habitable Worlds Observatory, NASA’s next envisioned flagship mission, with the goals of imaging and characterizing Earth-like exoplanets.
Project Lead: Dr. Michael Bottom, University of Hawai’i
Sponsoring Organization: NASA Strategic Astrophysics Technology (SAT) Program
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Last Updated Feb 18, 2025 Related Terms
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By NASA
This artist’s concept visualizes a super-Neptune world orbiting a low-mass star near the center of our Milky Way galaxy. Scientists recently discovered such a system that may break the current record for fastest exoplanet system, traveling at least 1.2 million miles per hour, or 540 kilometers per second.NASA/JPL-Caltech/R. Hurt (Caltech-IPAC) Astronomers may have discovered a scrawny star bolting through the middle of our galaxy with a planet in tow. If confirmed, the pair sets a new record for the fastest-moving exoplanet system, nearly double our solar system’s speed through the Milky Way.
The planetary system is thought to move at least 1.2 million miles per hour, or 540 kilometers per second.
“We think this is a so-called super-Neptune world orbiting a low-mass star at a distance that would lie between the orbits of Venus and Earth if it were in our solar system,” said Sean Terry, a postdoctoral researcher at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Since the star is so feeble, that’s well outside its habitable zone. “If so, it will be the first planet ever found orbiting a hypervelocity star.”
A paper describing the results, led by Terry, was published in The Astronomical Journal on February 10.
A Star on the Move
The pair of objects was first spotted indirectly in 2011 thanks to a chance alignment. A team of scientists combed through archived data from MOA (Microlensing Observations in Astrophysics) – a collaborative project focused on a microlensing survey conducted using the University of Canterbury Mount John Observatory in New Zealand — in search of light signals that betray the presence of exoplanets, or planets outside our solar system.
Microlensing occurs because the presence of mass warps the fabric of space-time. Any time an intervening object appears to drift near a background star, light from the star curves as it travels through the warped space-time around the nearer object. If the alignment is especially close, the warping around the object can act like a natural lens, amplifying the background star’s light.
This artist’s concept visualizes stars near the center of our Milky Way galaxy. Each has a colorful trail indicating its speed –– the longer and redder the trail, the faster the star is moving. NASA scientists recently discovered a candidate for a particularly speedy star, visualized near the center of this image, with an orbiting planet. If confirmed, the pair sets a record for fastest known exoplanet system.NASA/JPL-Caltech/R. Hurt (Caltech-IPAC) In this case, microlensing signals revealed a pair of celestial bodies. Scientists determined their relative masses (one is about 2,300 times heavier than the other), but their exact masses depend on how far away they are from Earth. It’s sort of like how the magnification changes if you hold a magnifying glass over a page and move it up and down.
“Determining the mass ratio is easy,” said David Bennett, a senior research scientist at the University of Maryland, College Park and NASA Goddard, who co-authored the new paper and led the original study in 2011. “It’s much more difficult to calculate their actual masses.”
The 2011 discovery team suspected the microlensed objects were either a star about 20 percent as massive as our Sun and a planet roughly 29 times heavier than Earth, or a nearer “rogue” planet about four times Jupiter’s mass with a moon smaller than Earth.
To figure out which explanation is more likely, astronomers searched through data from the Keck Observatory in Hawaii and ESA’s (European Space Agency’s) Gaia satellite. If the pair were a rogue planet and moon, they’d be effectively invisible – dark objects lost in the inky void of space. But scientists might be able to identify the star if the alternative explanation were correct (though the orbiting planet would be much too faint to see).
They found a strong suspect located about 24,000 light-years away, putting it within the Milky Way’s galactic bulge — the central hub where stars are more densely packed. By comparing the star’s location in 2011 and 2021, the team calculated its high speed.
This Hubble Space Telescope image shows a bow shock around a very young star called LL Ori. Named for the crescent-shaped wave made by a ship as it moves through water, a bow shock can be created in space when two streams of gas collide. Scientists think a similar feature may be present around a newfound star that could be traveling at least 1.2 million miles per hour, or 540 kilometers per second. Traveling at such a high velocity in the galactic bulge (the central part of the galaxy) where gas is denser could generate a bow shock. NASA and The Hubble Heritage Team (STScI/AURA); Acknowledgment: C. R. O’Dell (Vanderbilt University) But that’s just its 2D motion; if it’s also moving toward or away from us, it must be moving even faster. Its true speed may even be high enough to exceed the galaxy’s escape velocity of just over 1.3 million miles per hour, or about 600 kilometers per second. If so, the planetary system is destined to traverse intergalactic space many millions of years in the future.
“To be certain the newly identified star is part of the system that caused the 2011 signal, we’d like to look again in another year and see if it moves the right amount and in the right direction to confirm it came from the point where we detected the signal,” Bennett said.
“If high-resolution observations show that the star just stays in the same position, then we can tell for sure that it is not part of the system that caused the signal,” said Aparna Bhattacharya, a research scientist at the University of Maryland, College Park and NASA Goddard who co-authored the new paper. “That would mean the rogue planet and exomoon model is favored.”
NASA’s upcoming Nancy Grace Roman Space Telescope will help us find out how common planets are around such speedy stars, and may offer clues to how these systems are accelerated. The mission will conduct a survey of the galactic bulge, pairing a large view of space with crisp resolution.
“In this case we used MOA for its broad field of view and then followed up with Keck and Gaia for their sharper resolution, but thanks to Roman’s powerful view and planned survey strategy, we won’t need to rely on additional telescopes,” Terry said. “Roman will do it all.”
Download additional images and video from NASA’s Scientific Visualization Studio.
By Ashley Balzer
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Media contact:
Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, Md.
301-286-1940
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Last Updated Feb 10, 2025 EditorAshley BalzerContactAshley Balzerashley.m.balzer@nasa.govLocationGoddard Space Flight Center Related Terms
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By NASA
Almost a decade ago, then-grad student Kyle Helson contributed to early paperwork for NASA’s EXCITE mission. As a scientist at Goddard, Helson helped make this balloon-based telescope a reality: EXCITE launched successfully on Aug. 31.
Name: Kyle Helson
Title: Assistant Research Scientist
Organization: Observational Cosmology Lab (Code 665), via UMBC and the GESTAR II cooperative agreement with NASA Goddard
Dr. Kyle Helson is an assistant research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Photo credit: Dr. Amy Bender How did you know you wanted to work at NASA Goddard?
When I was finishing my physics Ph.D. at Brown University in 2016, I was talking to Ed Wollack and Dave Chuss at Goddard about the NASA postdoc program, and they suggested I apply. Luckily, I got the postdoc fellowship to come here to Goddard to work on cosmic microwave background detector testing and other related research.
I don’t think I would have realized or been interested in coming here had I not had that NASA Space Technology Research Fellowship when I was in grad school and gotten the opportunity to spend some time here and work with Ed and Dave.
What is the name of your team that you’re working with right now?
One of the projects I work on is the Exoplanet Climate Infrared TELescope (EXCITE). EXCITE is a scientific balloon-borne telescope that is designed to measure the spectra of hot, Jupiter-like exoplanet atmospheres in near-infrared light.
Related: NASA’s EXCITE Mission Prepared for Scientific Balloon Flight What is your role for that?
I do a little bit of everything. During grad school, I worked on the first few iterations of the proposal for EXCITE back in 2015 and 2016.
Over the past few years here at Goddard, I’ve been responsible for parts of a lot of the different subsystems like the cryogenic receiver, the gondola, the electronics, and integration and testing of the whole payload.
Last year, we went to Fort Sumner, New Mexico, for an engineering flight. Unfortunately, we were not able to fly for weather reasons. We went back last month, and I was again part of the field deployment team. We take the whole instrument, break it down, carefully ship it all out to New Mexico, put it back together, test it, and get it ready for a flight.
Kyle Helson (far right) and part of the EXCITE team stand in front of EXCITE Fort Sumner, New Mexico in Oct. 2023. EXCITE successfully launched on Aug. 31, 2024. Photo credit: Annalies Kleyheeg What is most interesting to you about your role here at Goddard?
What I like about working on a project like EXCITE is that we get to kind of do a little bit of everything.
We’ve been able to see the experiment from concept and design to actually getting built, tested and hopefully flown and then subsequent data analysis after the flight. What I think is really fun is being able be with an experiment for the entire life cycle.
How do you help support Goddard’s mission?
We’re studying exoplanets, which definitely fits within the scientific mission of Goddard. We’re also a collaboration between Goddard other academic institutions, like Arizona State, like Brown University, Cornell, and several other places, and so we’re also members of the larger scientific research community beyond NASA.
We also have a number of graduate students working on EXCITE. Ballooning is a good platform for training students and young researchers to learn how to build and design instruments, do data analysis, etc. One of the missions of NASA and Goddard is to train early career scientists like graduate students and post docs, and balloons provide a good platform for that as well.
Balloon missions like EXCITE also provide a good platform for technology advancement and demonstration in preparation for future satellite missions.
How did you know cosmology was what you wanted to pursue?
When I was a kid, I loved space. I wanted to be an astronaut when I was a kid. I even went to space camp.
The first time I ever got to see physics was a middle-school science class. That was the first time we ever learned physics or astronomy that was deeper than just identifying planets or constellations. We started to learn how we could use math to measure or predict experiments.
When I was in college, I remember talking to my undergraduate academic adviser, Glenn Starkman, and talking about what research I might like to do over the summer between sophomore and junior year of college. I wasn’t really sure what I wanted to do or what I was interested in, and he suggested I talk to some of the professors doing astrophysics and cosmology research and see if they had space for me in their lab.
I ended up finding a great opportunity working in a research lab in college — so it was working in the physics department in Case Western.
That’s where I first started learning about computer-aided design (CAD), and designing things in CAD, and that’s where I first learned how things get made in a machine shop, like on a mill, or a lathe. These skills have come in handy ever since, because I do a lot of design work in the lab. And I was lucky growing up that my dad was really hands-on and liked to fix things and build things and he taught me a lot of those skills as well.
“When I was a kid, I loved space,” said Kyle Helson. “I wanted to be an astronaut when I was a kid. I even went to space camp.”Photo courtesy of Kyle Helson Who has influenced you in your life?
My dad had a big influence. I think all the different people I’ve had the opportunity to learn from and work with who have been mentors along the way. My research advisers, professor John Ruhl in college, professor Greg Tucker in grad school, and Dr. Ed Wollack as a postdoc have all been very influential. Additionally, I have had the opportunity to work with a lot of very good post docs and research scientists during my career, Dr. Asad Aboobaker, Dr. Britt Reichborn-Kjennerud, Dr. Michele Limon, among others.
Throughout a career, there are tons of other people on the way from whom you pick up little things here and there that stick with you. You look back and you realize five years later you still do this one thing a certain way because someone helped you and taught you this skill or technique.
Where is a place you’d like to travel to?
Since I was lucky enough to go to Antarctica in graduate school, I figured that is the hardest continent to travel to, so now I have a mission to go to every continent. I’ve been to North America, I’ve been to South America, I’ve been to Asia, Europe, and Australia and New Zealand, but I’ve never been to Africa.
Kyle Helson (second from left) races the keirin at the Valley Preferred Cycling Center in Breinigsville, PA. Photo Credit Dr. Vishrut Garg What are your hobbies, or what do you enjoy doing?
I’m a competitive track cyclist. I started racing bikes in collegiate racing as a grad student at Brown. Many summers I’ve spent many weekends driving and flying all over the U.S. to race in the biggest track cycling events in the country.
What would be your three-word-memoir?
Curious, compassionate, cat-dad.
By Tayler Gilmore
NASA’s Goddard Space Flight Center in Greenbelt, Md
Conversations With Goddard is a collection of Q&A profiles highlighting the breadth and depth of NASA’s Goddard Space Flight Center’s talented and diverse workforce. The Conversations have been published twice a month on average since May 2011. Read past editions on Goddard’s “Our People” webpage.
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Last Updated Sep 10, 2024 EditorMadison OlsonContactRob Garnerrob.garner@nasa.govLocationGoddard Space Flight Center Related Terms
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By NASA
5 min read
How NASA Citizen Science Fuels Future Exoplanet Research
This artist’s concept shows the exoplanet K2-33b transiting its host star. Many citizen science projects at NASA invite the public to use transit data to make discoveries about exoplanets. NASA/JPL-Caltech NASA’s upcoming flagship astrophysics missions, the Nancy Grace Roman Space Telescope and the Habitable Worlds Observatory, will study planets outside our solar system, known as exoplanets. Over 5,000 exoplanets have been confirmed to date — and given that scientists estimate at least one exoplanet exists for every star in the sky, the hunt has just begun. Exoplanet discoveries from Roman and the Habitable Worlds Observatory may not be made only by professional researchers, but also by interested members of the public, known as citizen scientists.
Exoplanet research has a long involvement with citizen science. NASA’s TESS (Transiting Exoplanet Survey Satellite) mission and now-retired Kepler mission, which are responsible for the vast majority of exoplanet discoveries to date, both made observations freely available to the public immediately after processing. This open science policy paved the way for the public to get involved with NASA’s exoplanet science.
NASA’s Planet Hunters TESS project invites the public to classify exoplanet light curves from TESS online. Another project, Exoplanet Watch, allows citizen scientists to gather data about known exoplanets, submit their observations to NASA’s public data archive, and receive credit if their observation is used in a scientific paper. Participants don’t even need their own telescope — Exoplanet Watch also curates data from robotic telescopes for users to process.
Artist’s concept of NASA’s TESS (Transiting Exoplanet Survey Satellite). Data from TESS have been used in citizen science projects. NASA’s Goddard Space Flight Center “Anyone across the world who has access to a smartphone or a laptop can fully participate in a lot of these citizen science efforts to help us learn more about the cosmos,” said Rob Zellem, the project lead and project scientist for Exoplanet Watch and astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
NASA’s citizen science projects have discovered several new planets from Kepler and TESS data. They have also helped scientists refine the best time to observe important targets, saving hours of precious observation time on current flagship missions like NASA’s James Webb Space Telescope.
Roman and the Habitable Worlds Observatory provide even more possibilities for citizen science. Expected to launch by May 2027, Roman will discover exoplanets through direct imaging, transits, and gravitational microlensing. Following that, the Habitable Worlds Observatory will take direct images of stars in our solar neighborhood to find potentially habitable planets and study their atmospheres.
The general public can get Roman data as quickly as I can as a scientist working on the mission.
Rob Zellem
Exoplanet Watch Project Lead and Project Scientist; Nancy Grace Roman Space Telescope Deputy Project Scientist for Communications
Like Kepler and TESS before them, data from Roman and the Habitable Worlds Observatory will be available to both the scientific community and the public immediately after processing. With Roman’s surveys expected to deliver a terabyte of data to Earth every day — over 17 times as much as Webb — there is a huge opportunity for the public to help sift through the information.
“The general public can get Roman data as quickly as I can as a scientist working on the mission,” said Zellem, who also serves as Roman’s deputy project scientist for communications at NASA Goddard. “It truly makes Roman a mission for everyone and anyone.”
Although the Habitable Worlds Observatory’s full capabilities and instrumentation have yet to be finalized, the inclusion of citizen science is expected to continue. The team behind the mission is embracing a community-oriented planning approach by opening up working groups to volunteers who want to contribute.
“It’s already setting the tone for open science with the Habitable Worlds Observatory,” said Megan Ansdell, the program scientist for the mission at NASA Headquarters in Washington. “The process is as open as possible, and these working groups are open to anybody in the world who wants to join.” There are already over 1,000 community working group members participating, some of whom are citizen scientists.
The Roman Coronagraph, photographed during testing at NASA’s Jet Propulsion Lab in Southern California, is a technology demonstration designed to block starlight and allow scientists to see the faint light from planets outside our solar system. It represents one of multiple ways that Roman will contribute to exoplanet research. NASA/JPL-Caltech Future citizen science initiatives may be combined with cutting-edge tools such as artificial intelligence (AI) for greater efficacy. “AI can be exceptionally powerful in terms of classification and identifying anomalous things,” said Joshua Pepper, the deputy program scientist for the Habitable Worlds Observatory at NASA Headquarters. “But the evaluation of what those anomalous things are often requires human insight, intervention, and review, and I think that could be a really fantastic area for citizen scientists to participate.”
Before Roman and the Habitable Worlds Observatory launch, exoplanet citizen scientists still have plenty of data to analyze from the Kepler and TESS satellites, but the contributions of the community will become even more important when data begin pouring in from the new missions. As Zellem said, “We’re in a golden age of exoplanet science right now.”
NASA’s citizen science projects are collaborations between scientists and interested members of the public and do not require U.S. citizenship. Through these collaborations, volunteers (known as citizen scientists) have helped make thousands of important scientific discoveries. To get involved with a project, visit NASA’s Citizen Science page.
By Lauren Leese
Web Content Strategist for the Office of the Chief Science Data Officer
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Last Updated Aug 08, 2024 Related Terms
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By European Space Agency
An international team of astronomers using the NASA/ESA/CSA James Webb Space Telescope have directly imaged an exoplanet roughly 12 light-years from Earth. While there were hints that the planet existed, it had not been confirmed until Webb imaged it. The planet is one of the coldest exoplanets observed to date.
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