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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
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Artist concept highlighting the novel approach proposed by the 2025 NIAC awarded selection of Beholding Black Hole Power with the Accretion Explorer Interferometer concept.NASA/Kimberly Weaver Kimberly Weaver
NASA Goddard Space Flight Center
Some of the most enigmatic objects in the Universe are giant supermassive black holes (SMBH). Yet after 30 years of study, we don’t know precisely how these objects produce their power. This requires observations at X-ray wavelengths. The state-of-the-art for X-ray images is Chandra (~0.5-1 arcsecond resolution) but this is insufficient to image regions near SMBH where the most energetic behavior occurs. The Accretion Explorer (AE) is a mission architecture that will shatter new ground by creating X-ray images at scientifically crucial energies of 0.7-1.2 keV, 1.5-2.5 keV, 6-7 keV, up to 6 orders of magnitude better than Chandra, and will offer imaging at 4-5 orders of magnitude better than JWST (IR) and HST(optical/UV). The specific X-ray energy bands we are proposing to cover contain vital X-ray line signatures that can distinguish between SMBH activity and stellar processes. The AE NIAC concept would be a game changer for NASA and astrophysics. X-ray interferometry will challenge and change the conversation around future mission possibilities for NASA’s flagships. It will also influence the Astrophysics 2030 Decadal Survey and will significantly contribute to our scientific knowledge base in astrophysics and other fields. AE has tremendous potential to generate enthusiasm for future missions and the potential to build advocacy to support it within NASA, society, and the aerospace community.
Alternative approaches to ultra high-resolution X-ray imaging technology are not currently being funded. Our study will focus on a large free-flying X-ray interferometer. We will design a multiple spacecraft system that provides the architecture to align individual mirror pair baseline groupings provided by individual collector spacecraft, with the pointing precision to achieve micro-arcsecond resolution. Our study will assess the required pointing stability and determine optimal ways to nest and mount the collecting mirror flats within mirror modules. We will assess the required size for the detector array(s) to accommodate the wavelength coverage for detecting fringes, study how images will be created from fringes, and produce a simulated image from a design with accompanying optical element tolerance tables. We will document alternative approaches, how new factors substantially differentiate AE from prior efforts for X-ray interferometry, and identify technical hurdles.
As a result of performing this study, there are notable engineering benefits that can contribute to space missions, even if the concept is shown to be infeasible. These include establishing how small baseline interferometers can be flown with less risk in terms of spacing and tethering mirror modules, studies of very high levels of pointing precision for space-based interferometers, and extreme stability on target. Producing a simulated image from this design with accompanying tolerance tables can inform other space-based interferometry designs.
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Last Updated Jan 10, 2025 EditorLoura Hall Related Terms
NASA Innovative Advanced Concepts (NIAC) Program NIAC Studies Keep Exploring Discover More NIAC Topics
Space Technology Mission Directorate
NASA Innovative Advanced Concepts
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By NASA
2 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Artist concept highlighting the novel approach proposed by the 2025 NIAC awarded selection of TOBIAS: Tethered Observatory for Balloon-based Imaging and Atmospheric Sampling concept.NASA/Ben Hockman Ben Hockman
NASA Jet Propulsion Laboratory
A basketball-sized towbody containing a camera, atmospheric sampling instruments, and support hardware is suspended on a multi-kilometer tether from a high-altitude balloon in the Venusian atmosphere, allowing it to peer beneath the dense cloud layer and image the surface at high resolution. The towbody harvests energy from the differential wind shear via an onboard wind turbine in order to power onboard instruments and active cooling system. Aerodynamic surfaces interacting with the relative wind shears of ~10 m/s allow the towbody to maintain stable pointing for imaging. This Phase I study will focus on four key feasibility aspects of the towbody system: (1) the tether system, including tether design, deployment system, and drag due to atmospheric wind shear, (2) towbody attitude stability, including its aerodynamic design and vibration suppression, (3) the power and thermal system for surviving the harsh Venusian atmosphere, and (4) the mission architecture and systems engineering aspects, particularly communications, towbody deployment, gondola interfaces, and the concept of operations. This “Tethered Observatory for Balloon-based Imaging and Atmospheric Sampling (TOBIAS)” would transform our understanding of the nature and evolution of Venus by enabling high resolution and spatial coverage nighttime IR imaging of surface geology, including active and past volcanism.
2025 Selections
Facebook logo @NASATechnology @NASA_Technology
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Last Updated Jan 10, 2025 EditorLoura Hall Related Terms
NASA Innovative Advanced Concepts (NIAC) Program NIAC Studies Keep Exploring Discover More NIAC Topics
Space Technology Mission Directorate
NASA Innovative Advanced Concepts
NIAC Funded Studies
About NIAC
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By NASA
An artist’s concept of the Earth, Moon, and Mars.Credit: NASA As NASA develops a blueprint for space exploration throughout the solar system for the benefit of humanity, the agency released several new documents Friday updating its Moon to Mars architecture. The roadmap sets NASA on course for long-term lunar exploration under the Artemis campaign in preparation for future crewed missions to Mars.
Following an Architecture Concept Review, the 2024 updates include a revision of NASA’s Architecture Definition Document which details technical approaches and processes of the agency’s exploration plans, an executive overview, and 12 new white papers on key Moon to Mars topics.
“NASA’s Architecture Concept Review process is critical to getting us on a path to mount a human mission to Mars,” said NASA Associate Administrator Jim Free. “We’re taking a methodical approach to mapping out the decisions we need to make, understanding resource and technological trades, and ensuring we are listening to feedback from stakeholders.”
One newly released white paper highlights NASA’s decision to use fission power as the primary source of power on the Martian surface to sustain crews — the first of seven key decisions necessary for human Mars exploration. Fission power is a form of nuclear power unaffected by day and night cycles or potential dust storms on Mars.
New additions this year also include a broader, prioritized list of key architecture decisions that need to be made early in NASA’s plans to send humans to the Red Planet. Two new elements are now part of the agency’s Moon to Mars architecture — a lunar surface cargo lander and an initial lunar surface habitat. The lunar surface cargo lander will deliver logistics items, science and technology payloads, communications systems, and more. The initial surface habitat will house astronauts on the lunar surface to extend the crew size, range, and duration of exploration missions and enable crewed and uncrewed science opportunities.
The newest revision of the Architecture Definition Document adds more information about NASA’s decision road mapping process — how the agency decides which decisions must be made early in the planning process based on impacts to subsequent decisions — and a list of architecture-driven opportunities that help technology development organizations prioritize research into new technologies that will enable the Moon to Mars architecture.
“Identifying and analyzing high-level architecture decisions are the first steps to realizing a crewed Mars exploration campaign,” said Catherine Koerner, associate administrator, Exploration Systems Development Mission Directorate, NASA Headquarters in Washington. “Each yearly assessment cycle as part of our architecture process is moving us closer to ensuring we have a well thought out plan to accomplish our exploration objectives.”
NASA’s Moon to Mars architecture approach incorporates feedback from U.S. industry, academia, international partners, and the NASA workforce. The agency typically releases a series of technical documents at the end of its annual analysis cycle, including an update of the Architecture Definition Document and white papers that elaborate on frequently raised topics.
Under NASA’s Artemis campaign, the agency will establish the foundation for long-term scientific exploration at the Moon, land the next Americans and first international partner astronaut on the lunar surface, and prepare for human expeditions to Mars for the benefit of all.
For NASA’s Moon to Mars architecture documents, visit:
https://www.nasa.gov/moontomarsarchitecture
-end-
Rachel Kraft / Kathryn Hambleton
Headquarters, Washington
202-358-1600
rachel.h.kraft@nasa.gov / kathryn.a.hambleton@nasa.gov
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Last Updated Dec 13, 2024 EditorJessica TaveauLocationNASA Headquarters Related Terms
Exploration Systems Development Mission Directorate Artemis Earth's Moon Mars View the full article
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By European Space Agency
The latest edition of ESA Impact is here
Your interactive gateway to the most captivating stories and stunning visuals from ESA
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