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By NASA
7 min read
A New Alloy is Enabling Ultra-Stable Structures Needed for Exoplanet Discovery
A unique new material that shrinks when it is heated and expands when it is cooled could help enable the ultra-stable space telescopes that future NASA missions require to search for habitable worlds.
Advancements in material technologies are needed to meet the science needs of the next great observatories. These observatories will strive to find, identify, and study exoplanets and their ability to support life. Credit: NASA JPL One of the goals of NASA’s Astrophysics Division is to determine whether we are alone in the universe. NASA’s astrophysics missions seek to answer this question by identifying planets beyond our solar system (exoplanets) that could support life. Over the last two decades, scientists have developed ways to detect atmospheres on exoplanets by closely observing stars through advanced telescopes. As light passes through a planet’s atmosphere or is reflected or emitted from a planet’s surface, telescopes can measure the intensity and spectra (i.e., “color”) of the light, and can detect various shifts in the light caused by gases in the planetary atmosphere. By analyzing these patterns, scientists can determine the types of gasses in the exoplanet’s atmosphere.
Decoding these shifts is no easy task because the exoplanets appear very near their host stars when we observe them, and the starlight is one billion times brighter than the light from an Earth-size exoplanet. To successfully detect habitable exoplanets, NASA’s future Habitable Worlds Observatory will need a contrast ratio of one to one billion (1:1,000,000,000).
Achieving this extreme contrast ratio will require a telescope that is 1,000 times more stable than state-of-the-art space-based observatories like NASA’s James Webb Space Telescope and its forthcoming Nancy Grace Roman Space Telescope. New sensors, system architectures, and materials must be integrated and work in concert for future mission success. A team from the company ALLVAR is collaborating with NASA’s Marshall Space Flight Center and NASA’s Jet Propulsion Laboratory to demonstrate how integration of a new material with unique negative thermal expansion characteristics can help enable ultra-stable telescope structures.
Material stability has always been a limiting factor for observing celestial phenomena. For decades, scientists and engineers have been working to overcome challenges such as micro-creep, thermal expansion, and moisture expansion that detrimentally affect telescope stability. The materials currently used for telescope mirrors and struts have drastically improved the dimensional stability of the great observatories like Webb and Roman, but as indicated in the Decadal Survey on Astronomy and Astrophysics 2020 developed by the National Academies of Sciences, Engineering, and Medicine, they still fall short of the 10 picometer level stability over several hours that will be required for the Habitable Worlds Observatory. For perspective, 10 picometers is roughly 1/10th the diameter of an atom.
NASA’s Nancy Grace Roman Space Telescope sits atop the support structure and instrument payloads. The long black struts holding the telescope’s secondary mirror will contribute roughly 30% of the wave front error while the larger support structure underneath the primary mirror will contribute another 30%.
Credit: NASA/Chris Gunn
Funding from NASA and other sources has enabled this material to transition from the laboratory to the commercial scale. ALLVAR received NASA Small Business Innovative Research (SBIR) funding to scale and integrate a new alloy material into telescope structure demonstrations for potential use on future NASA missions like the Habitable Worlds Observatory. This alloy shrinks when heated and expands when cooled—a property known as negative thermal expansion (NTE). For example, ALLVAR Alloy 30 exhibits a -30 ppm/°C coefficient of thermal expansion (CTE) at room temperature. This means that a 1-meter long piece of this NTE alloy will shrink 0.003 mm for every 1 °C increase in temperature. For comparison, aluminum expands at +23 ppm/°C.
While other materials expand while heated and contract when cooled, ALLVAR Alloy 30 exhibits a negative thermal expansion, which can compensate for the thermal expansion mismatch of other materials. The thermal strain versus temperature is shown for 6061 Aluminum, A286 Stainless Steel, Titanium 6Al-4V, Invar 36, and ALLVAR Alloy 30.
Because it shrinks when other materials expand, ALLVAR Alloy 30 can be used to strategically compensate for the expansion and contraction of other materials. The alloy’s unique NTE property and lack of moisture expansion could enable optic designers to address the stability needs of future telescope structures. Calculations have indicated that integrating ALLVAR Alloy 30 into certain telescope designs could improve thermal stability up to 200 times compared to only using traditional materials like aluminum, titanium, Carbon Fiber Reinforced Polymers (CFRPs), and the nickel–iron alloy, Invar.
The hexapod assembly with six ALLVAR Alloy struts was measured for long-term stability. The stability of the individual struts and the hexapod assembly were measured using interferometry at the University of Florida’s Institute for High Energy Physics and Astrophysics. The struts were found to have a length noise well below the proposed target for the success criteria for the project. Credit: (left) ALLVAR and (right) Simon F. Barke, Ph.D. To demonstrate that negative thermal expansion alloys can enable ultra-stable structures, the ALLVAR team developed a hexapod structure to separate two mirrors made of a commercially available glass ceramic material with ultra-low thermal expansion properties. Invar was bonded to the mirrors and flexures made of Ti6Al4V—a titanium alloy commonly used in aerospace applications—were attached to the Invar. To compensate for the positive CTEs of the Invar and Ti6Al4V components, an NTE ALLVAR Alloy 30 tube was used between the Ti6Al4V flexures to create the struts separating the two mirrors. The natural positive thermal expansion of the Invar and Ti6Al4V components is offset by the negative thermal expansion of the NTE alloy struts, resulting in a structure with an effective zero thermal expansion.
The stability of the structure was evaluated at the University of Florida Institute for High Energy Physics and Astrophysics. The hexapod structure exhibited stability well below the 100 pm/√Hz target and achieved 11 pm/√Hz. This first iteration is close to the 10 pm stability required for the future Habitable Worlds Observatory. A paper and presentation made at the August 2021 Society of Photo-Optical Instrumentation Engineers conference provides details about this analysis.
Furthermore, a series of tests run by NASA Marshall showed that the ultra-stable struts were able to achieve a near-zero thermal expansion that matched the mirrors in the above analysis. This result translates into less than a 5 nm root mean square (rms) change in the mirror’s shape across a 28K temperature change.
The ALLVAR enabled Ultra-Stable Hexapod Assembly undergoing Interferometric Testing between 293K and 265K (right). On the left, the Root Mean Square (RMS) changes in the mirror’s surface shape are visually represented. The three roughly circular red areas are caused by the thermal expansion mismatch of the invar bonding pads with the ZERODUR mirror, while the blue and green sections show little to no changes caused by thermal expansion. The surface diagram shows a less than 5 nanometer RMS change in mirror figure. Credit: NASA’s X-Ray and Cryogenic Facility [XRCF] Beyond ultra-stable structures, the NTE alloy technology has enabled enhanced passive thermal switch performance and has been used to remove the detrimental effects of temperature changes on bolted joints and infrared optics. These applications could impact technologies used in other NASA missions. For example, these new alloys have been integrated into the cryogenic sub-assembly of Roman’s coronagraph technology demonstration. The addition of NTE washers enabled the use of pyrolytic graphite thermal straps for more efficient heat transfer. ALLVAR Alloy 30 is also being used in a high-performance passive thermal switch incorporated into the UC Berkeley Space Science Laboratory’s Lunar Surface Electromagnetics Experiment-Night (LuSEE Night) project aboard Firefly Aerospace’s Blue Ghost Mission 2, which will be delivered to the Moon through NASA’s CLPS (Commercial Lunar Payload Services) initiative. The NTE alloys enabled smaller thermal switch size and greater on-off heat conduction ratios for LuSEE Night.
Through another recent NASA SBIR effort, the ALLVAR team worked with NASA’s Jet Propulsion Laboratory to develop detailed datasets of ALLVAR Alloy 30 material properties. These large datasets include statistically significant material properties such as strength, elastic modulus, fatigue, and thermal conductivity. The team also collected information about less common properties like micro-creep and micro-yield. With these properties characterized, ALLVAR Alloy 30 has cleared a major hurdle towards space-material qualification.
As a spinoff of this NASA-funded work, the team is developing a new alloy with tunable thermal expansion properties that can match other materials or even achieve zero CTE. Thermal expansion mismatch causes dimensional stability and force-load issues that can impact fields such as nuclear engineering, quantum computing, aerospace and defense, optics, fundamental physics, and medical imaging. The potential uses for this new material will likely extend far beyond astronomy. For example, ALLVAR developed washers and spacers, are now commercially available to maintain consistent preloads across extreme temperature ranges in both space and terrestrial environments. These washers and spacers excel at counteracting the thermal expansion and contraction of other materials, ensuring stability for demanding applications.
For additional details, see the entry for this project on NASA TechPort.
Project Lead: Dr. James A. Monroe, ALLVAR
The following NASA organizations sponsored this effort: NASA Astrophysics Division, NASA SBIR Program funded by the Space Technology Mission Directorate (STMD).
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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 6 Min Read Frigid Exoplanet in Strange Orbit Imaged by NASA’s Webb
This image of exoplanet 14 Herculis c was taken by NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera). A star symbol marks the location of the host star 14 Herculis, whose light has been blocked by a coronagraph on NIRCam (shown here as a dark circle outlined in white). Credits:
NASA, ESA, CSA, STScI, W. Balmer (JHU), D. Bardalez Gagliuffi (Amherst College) A planetary system described as abnormal, chaotic, and strange by researchers has come into clearer view with NASA’s James Webb Space Telescope. Using Webb’s NIRCam (Near-Infrared Camera), researchers have successfully imaged one of two known planets surrounding the star 14 Herculis, located 60 light-years away from Earth in our own Milky Way galaxy.
The exoplanet, 14 Herculis c, is one of the coldest imaged to date. While there are nearly 6,000 exoplanets that have been discovered, only a small number of those have been directly imaged, most of those being very hot (think hundreds or even thousands of degrees Fahrenheit). The new data suggests 14 Herculis c, which weighs about 7 times the planet Jupiter, is as cool as 26 degrees Fahrenheit (minus 3 degrees Celsius).
Image: 14 Herculis c (NIRCam)
This image of exoplanet 14 Herculis c was taken by NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera). A star symbol marks the location of the host star 14 Herculis, whose light has been blocked by a coronagraph on NIRCam (shown here as a dark circle outlined in white). NASA, ESA, CSA, STScI, W. Balmer (JHU), D. Bardalez Gagliuffi (Amherst College) The team’s results covering 14 Herculis c have been submitted to The Astrophysical Journal Letters and were presented in a press conference Tuesday at the 246th meeting of the American Astronomical Society in Anchorage, Alaska.
“The colder an exoplanet, the harder it is to image, so this is a totally new regime of study that Webb has unlocked with its extreme sensitivity in the infrared,” said William Balmer, co-first author of the new paper and graduate student at Johns Hopkins University. “We are now able to add to the catalog of not just hot, young exoplanets imaged, but older exoplanets that are far colder than we’ve directly seen before Webb.”
Webb’s image of 14 Herculis c also provides insights into a planetary system unlike most others studied in detail with Webb and other ground- and space-based `observatories. The central star, 14 Herculis, is almost Sun-like – it is similar in age and temperature to our own Sun, but a little less massive and cooler.
There are two planets in this system – 14 Herculis b is closer to the star, and covered by the coronagraphic mask in the Webb image. These planets don’t orbit each other on the same plane like our solar system. Instead, they cross each other like an ‘X’, with the star being at the center. That is, the orbital planes of the two planets are inclined relative to one another at an angle of about 40 degrees. The planets tug and pull at one another as they orbit the star.
This is the first time an image has ever been snapped of an exoplanet in such a mis-aligned system.
Scientists are working on several theories for just how the planets in this system got so “off track.” One of the leading concepts is that the planets scattered after a third planet was violently ejected from the system early in its formation.
“The early evolution of our own solar system was dominated by the movement and pull of our own gas giants,” added Balmer. “They threw around asteroids and rearranged other planets. Here, we are seeing the aftermath of a more violent planetary crime scene. It reminds us that something similar could have happened to our own solar system, and that the outcomes for small planets like Earth are often dictated by much larger forces.”
Understanding the Planet’s Characteristics With Webb
Webb’s new data is giving researchers further insights into not just the temperature of 14 Herculis c, but other details about the planet’s orbit and atmosphere.
Findings indicate the planet orbits around 1.4 billion miles from the host star in a highly elliptical, or football-shaped orbit, closer in than previous estimates. This is around 15 times farther from the Sun than Earth. On average, this would put 14 Herculis c between Saturn and Uranus in our solar system.
The planet’s brightness at 4.4 microns measured using Webb’s coronagraph, combined with the known mass of the planet and age of the system, hints at some complex atmospheric dynamics at play.
“If a planet of a certain mass formed 4 billion years ago, then cooled over time because it doesn’t have a source of energy keeping it warm, we can predict how hot it should be today,” said Daniella C. Bardalez Gagliuffi of Amherst College, co-first author on the paper with Balmer. “Added information, like the perceived brightness in direct imaging, would in theory support this estimate of the planet’s temperature.”
However, what researchers expect isn’t always reflected in the results. With 14 Herculis c, the brightness at this wavelength is fainter than expected for an object of this mass and age. The research team can explain this discrepancy, though. It’s called carbon disequilibrium chemistry, something often seen in brown dwarfs.
“This exoplanet is so cold, the best comparisons we have that are well-studied are the coldest brown dwarfs,” Bardalez Gagliuffi explained. “In those objects, like with 14 Herculis c, we see carbon dioxide and carbon monoxide existing at temperatures where we should see methane. This is explained by churning in the atmosphere. Molecules made at warmer temperatures in the lower atmosphere are brought to the cold, upper atmosphere very quickly.”
Researchers hope Webb’s image of 14 Herculis c is just the beginning of a new phase of investigation into this strange system.
While the small dot of light obtained by Webb contains a plethora of information, future spectroscopic studies of 14 Herculis could better constrain the atmospheric properties of this interesting planet and help researchers understand the dynamics and formation pathways of the system.
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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Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Hannah Braun – hbraun@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
Christine Pulliam – cpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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Exoplanets Astrophysics Goddard Space Flight Center James Webb Space Telescope (JWST) Science & Research Studying Exoplanets The Universe View the full article
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Explore This Section 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 Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning 6 Min Read NASA’s Webb Lifts Veil on Common but Mysterious Type of Exoplanet
This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like. It is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. Credits:
Illustration: NASA, ESA, CSA, Dani Player (STScI) Though they don’t orbit around our Sun, sub-Neptunes are the most common type of exoplanet, or planet outside our solar system, that have been observed in our galaxy. These small, gassy planets are shrouded in mystery…and often, a lot of haze. Now, by observing exoplanet TOI-421 b, NASA’s James Webb Space Telescope is helping scientists understand sub-Neptunes in a way that was not possible prior to the telescope’s launch.
“I had been waiting my entire career for Webb so that we could meaningfully characterize the atmospheres of these smaller planets,” said principal investigator Eliza Kempton of the University of Maryland, College Park. “By studying their atmospheres, we’re getting a better understanding of how sub-Neptunes formed and evolved, and part of that is understanding why they don’t exist in our solar system.”
Image A: Artist’s Concept of TOI-421 b
This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like. It is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. Illustration: NASA, ESA, CSA, Dani Player (STScI) Small, Cool, Shrouded in Haze
The existence of sub-Neptunes was unexpected before they were discovered by NASA’s retired Kepler space telescope in the last decade. Now, astronomers are trying to understand where these planets came from and why are they so common.
Before Webb, scientists had very little information on them. While sub-Neptunes are a few times larger than Earth, they are still much smaller than gas-giant planets and typically cooler than hot Jupiters, making them much more challenging to observe than their gas-giant counterparts.
A key finding prior to Webb was that most sub-Neptune atmospheres had flat or featureless transmission spectra. This means that when scientists observed the spectrum of the planet as it passed in front of its host star, instead of seeing spectral features – the chemical fingerprints that would reveal the composition of the atmosphere – they saw only a flat-line spectrum. Astronomers concluded from all of those flat-line spectra that at least certain sub-Neptunes were probably very highly obscured by either clouds or hazes.
Image B: Spectrum of TOI-421 b
A transmission spectrum captured by NASA’s James Webb Space Telescope reveals chemicals in the atmosphere of the hot sub-Neptune exoplanet TOI-421 b. Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI) A Different Kind of Sub-Neptune?
“Why did we observe this planet, TOI-421 b? It’s because we thought that maybe it wouldn’t have hazes,” said Kempton. “And the reason is that there were some previous data that implied that maybe planets over a certain temperature range were less enshrouded by haze or clouds than others.”
That temperature threshold is about 1,070 degrees Fahrenheit. Below that, scientists hypothesized that a complex set of photochemical reactions would occur between sunlight and methane gas, and that would trigger the haze. But hotter planets shouldn’t have methane and therefore perhaps shouldn’t have haze.
The temperature of TOI-421 b is about 1,340 degrees Fahrenheit, well above the presumed threshold. Without haze or clouds, researchers expected to see a clear atmosphere – and they did!
A Surprising Finding
“We saw spectral features that we attribute to various gases, and that allowed us to determine the composition of the atmosphere,” said the University of Maryland’s Brian Davenport, a third-year Ph.D. student who conducted the primary data analysis. “Whereas with many of the other sub-Neptunes that had been previously observed, we know their atmospheres are made of something, but they’re being blocked by haze.”
The team found water vapor in the planet’s atmosphere, as well as tentative signatures of carbon monoxide and sulfur dioxide. Then there are molecules they didn’t detect, such as methane and carbon dioxide. From the data, they can also infer that a large amount of hydrogen is in TOI-421 b’s atmosphere.
The lightweight hydrogen atmosphere was the big surprise to the researchers. “We had recently wrapped our mind around the idea that those first few sub-Neptunes observed by Webb had heavy-molecule atmospheres, so that had become our expectation, and then we found the opposite,” said Kempton. This suggests TOI-421 b may have formed and evolved differently from the cooler sub-Neptunes observed previously.
Is TOI-421 b Unique?
The hydrogen-dominated atmosphere is also interesting because it mimics the composition of TOI-421 b’s host star. “If you just took the same gas that made the host star, plopped it on top of a planet’s atmosphere, and put it at the much cooler temperature of this planet, you would get the same combination of gases. That process is more in line with the giant planets in our solar system, and it is different from other sub-Neptunes that have been observed with Webb so far,” said Kempton.
Aside from being hotter than other sub-Neptunes previously observed with Webb, TOI-421 b orbits a Sun-like star. Most of the other sub-Neptunes that have been observed so far orbit smaller, cooler stars called red dwarfs.
Is TOI-421b emblematic of hot sub-Neptunes orbiting Sun-like stars, or is it just that exoplanets are very diverse? To find out, the researchers would like to observe more hot sub-Neptunes to determine if this is a unique case or a broader trend. They hope to gain insights into the formation and evolution of these common exoplanets.
“We’ve unlocked a new way to look at these sub-Neptunes,” said Davenport. “These high-temperature planets are amenable to characterization. So by looking at sub-Neptunes of this temperature, we’re perhaps more likely to accelerate our ability to learn about these planets.”
The team’s findings appear on May 5 in the Astrophysical Journal Letters.
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
Downloads
Click any image to open a larger version.
View/Download all image products at all resolutions for this article from the Space Telescope Science Institute.
Media Contacts
Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Ann Jenkins – jenkins@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
Hannah Braun – hbraun@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
Related Information
Webb Blog: Reconnaissance of Potentially Habitable Worlds with NASA’s Webb
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Learn more about exoplanets
More Webb News
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Related For Kids
What is the Webb Telescope?
SpacePlace for Kids
En Español
Ciencia de la NASA
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James Webb Space Telescope
Webb is the premier observatory of the next decade, serving thousands of astronomers worldwide. It studies every phase in the…
Exoplanets
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Last Updated May 04, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
James Webb Space Telescope (JWST) Astrophysics Exoplanets Goddard Space Flight Center Science & Research The Universe View the full article
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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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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
Exoplanets Astrophysics Exoplanet Discoveries Exoplanet Science Goddard Space Flight Center Nancy Grace Roman Space Telescope Neptune-Like Exoplanets Science & Research Studying Exoplanets The Universe Explore More
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