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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
This artist’s concept shows a brown dwarf — an object larger than a planet but not massive enough to kickstart fusion in its core like a star. Brown dwarfs are hot when they form and may glow like this one, but over time they get closer in temperature to gas giant planets like Jupiter. NOIRLab/NSF/AURA/R. Proctor An unusual cosmic object is helping scientists better understand the chemistry hidden deep in Jupiter and Saturn’s atmospheres — and potentially those of exoplanets.
Why has silicon, one of the most common elements in the universe, gone largely undetected in the atmospheres of Jupiter, Saturn, and gas planets like them orbiting other stars? A new study using observations from NASA’s James Webb Space Telescope sheds light on this question by focusing on a peculiar object that astronomers discovered by chance in 2020 and called “The Accident.”
The results were published on Sept. 4 in the journal Nature.
As shown in this graphic, brown dwarfs can be far more massive than even large gas planets like Jupiter and Saturn. However, they tend to lack the mass that kickstarts nuclear fusion in the cores of stars, causing them to shine. NASA/JPL-Caltech The Accident is a brown dwarf, a ball of gas that’s not quite a planet and not quite a star. Even among its already hard-to-classify peers, The Accident has a perplexing mix of physical features, some of which have been previously seen in only young brown dwarfs and others seen only in ancient ones. Because of those features, it slipped past typical detection methods before being discovered five years ago by a citizen scientist participating in Backyard Worlds: Planet 9. The program lets people around the globe look for new discoveries in data from NASA’s now-retired NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer), which was managed by NASA’s Jet Propulsion Laboratory in Southern California.
The brown dwarf nicknamed “The Accident” can be seen moving in the bottom left corner of this video, which shows data from NASA’s now-retired NEOWISE (Near-Earth Object Wide-Field Infrared Survey Explorer), launched in 2009 with the moniker WISE. NASA/JPL-Caltech/Dan Caselden The Accident is so faint and odd that researchers needed NASA’s most powerful space observatory, Webb, to study its atmosphere. Among several surprises, they found evidence of a molecule they couldn’t initially identify. It turned out to be a simple silicon molecule called silane (SiH4). Researchers have long expected — but been unable — to find silane not only in our solar system’s gas giants, but also in the thousands of atmospheres belonging to brown dwarfs and to the gas giants orbiting other stars. The Accident is the first such object where this molecule has been identified.
Scientists are fairly confident that silicon exists in Jupiter and Saturn’s atmospheres but that it is hidden. Bound to oxygen, silicon forms oxides such as quartz that can seed clouds on hot gas giants, bearing a resemblance to dust storms on Earth. On cooler gas giants like Jupiter and Saturn, these types of clouds would sink far beneath lighter layers of water vapor and ammonia clouds, until any silicon-containing molecules are deep in the atmosphere, invisible even to the spacecraft that have studied those two planets up close.
Some researchers have also posited that lighter molecules of silicon, like silane, should be found higher up in these atmospheric layers, left behind like traces of flour on a baker’s table. That such molecules haven’t appeared anywhere except in a single, peculiar brown dwarf suggests something about the chemistry occurring in these environments.
“Sometimes it’s the extreme objects that help us understand what’s happening in the average ones,” said Faherty, a researcher at the American Museum of Natural History in New York City, and lead author on the new study.
Happy accident
Located about 50 light-years from Earth, The Accident likely formed 10 billion to 12 billion years ago, making it one of the oldest brown dwarfs ever discovered. The universe is about 14 billion years old, and at the time that The Accident developed, the cosmos contained mostly hydrogen and helium, with trace amounts of other elements, including silicon. Over eons, elements like carbon, nitrogen, and oxygen forged in the cores of stars, so planets and stars that formed more recently possess more of those elements.
Webb’s observations of The Accident confirm that silane can form in brown dwarf and planetary atmospheres. The fact that silane seems to be missing in other brown dwarfs and gas giant planets suggests that when oxygen is available, it bonds with silicon at such a high rate and so easily, virtually no silicon is left over to bond with hydrogen and form silane.
So why is silane in The Accident? The study authors surmise it is because far less oxygen was present in the universe when the ancient brown dwarf formed, resulting in less oxygen in its atmosphere to gobble up all the silicon. The available silicon would have bonded with hydrogen instead, resulting in silane.
“We weren’t looking to solve a mystery about Jupiter and Saturn with these observations,” said JPL’s Peter Eisenhardt, project scientist for the WISE (Wide-field Infrared Survey Explorer) mission, which was later repurposed as NEOWISE. “A brown dwarf is a ball of gas like a star, but without an internal fusion reactor, it gets cooler and cooler, with an atmosphere like that of gas giant planets. We wanted to see why this brown dwarf is so odd, but we weren’t expecting silane. The universe continues to surprise us.”
Brown dwarfs are often easier to study than gas giant exoplanets because the light from a faraway planet is typically drowned out by the star it orbits, while brown dwarfs generally fly solo. And the lessons learned from these objects extend to all kinds of planets, including ones outside our solar system that might feature potential signs of habitability.
“To be clear, we’re not finding life on brown dwarfs,” said Faherty. “But at a high level, by studying all of this variety and complexity in planetary atmospheres, we’re setting up the scientists who are one day going to have to do this kind of chemical analysis for rocky, potentially Earth-like planets. It might not specifically involve silicon, but they’re going to get data that is complicated and confusing and doesn’t fit their models, just like we are. They’ll have to parse all those complexities if they want to answer those big questions.”
More about WISE, Webb
A division of Caltech, JPL managed and operated WISE for NASA’s Science Mission Directorate. The mission was selected competitively under NASA’s Explorers Program managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland. The NEOWISE mission was a project of JPL and the University of Arizona in Tucson, supported by NASA’s Planetary Defense Coordination Office.
For more information about WISE, go to:
https://www.nasa.gov/mission_pages/WISE/main/index.html
The James Webb Space Telescope is the world’s premier space science observatory, and 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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Space Telescope Science Institute, Baltimore, Md.
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Last Updated Sep 09, 2025 Related Terms
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By NASA
Explore This Section Overview Science Science Findings Juno’s Orbits Spacecraft People Stories Multimedia JunoCam Images Jupiter hosts the brightest and most spectacular auroras in the Solar System. Near its poles, these shimmering lights offer a glimpse into how the planet interacts with the solar wind and moons swept by Jupiter’s magnetic field. Unlike Earth’s northern lights, the largest moons of Jupiter create their own auroral signatures in the planet’s atmosphere — a phenomenon that Earth’s Moon does not produce. These moon-induced auroras, known as “satellite footprints,” reveal how each moon interacts with its local space environment.
Juno capturing the marks on Jupiter of all four Galilean moons. The auroras related to each are labeled Io, Eur (for Europa), Gan (for Ganymede), and Cal (for Callisto). NASA/JPL-Caltech/SwRI/UVS team/MSSS/Gill/Jónsson/Perry/Hue/Rabia Before NASA’s Juno mission, three of Jupiter’s four largest moons, known as Galilean moons — Io, Europa, and Ganymede — were shown to produce these distinct auroral signatures. But Callisto, the most distant of the Galilean moons, remained a mystery. Despite multiple attempts using NASA’s Hubble Space Telescope, Callisto’s footprint had proven elusive, both because it is faint and because it most often lies atop the brighter main auroral oval, the region where auroras are displayed.
NASA’s Juno mission, orbiting Jupiter since 2016, offers unprecedented close-up views of these polar light shows. But to image Callisto’s footprint, the main auroral oval needs to move aside while the polar region is being imaged. And to bring to bear Juno’s arsenal of instruments studying fields and particles, the spacecraft’s trajectory must carry it across the magnetic field line linking Callisto and Jupiter.
These two events serendipitously occurred during Juno’s 22nd orbit of the giant planet, in September 2019, revealing Callisto’s auroral footprint and providing a sample of the particle population, electromagnetic waves, and magnetic fields associated with the interaction.
Jupiter’s magnetic field extends far beyond its major moons, carving out a vast region (magnetosphere) enveloped by, and buffeted by, the solar wind streaming from our Sun. Just as solar storms on Earth push the northern lights to more southern latitudes, Jupiter’s auroras are also affected by our Sun’s activity. In September 2019, a massive, high-density solar stream buffeted Jupiter’s magnetosphere, briefly revealing — as the auroral oval moved toward Jupiter’s equator — a faint but distinct signature associated with Callisto. This discovery finally confirms that all four Galilean moons leave their mark on Jupiter’s atmosphere, and that Callisto’s footprints are sustained much like those of its siblings, completing the family portrait of the Galilean moon auroral signatures.
An international team of scientists led by Jonas Rabia of the Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS, CNES, in Toulouse, France, published their paper on the discovery, “In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft,” in the journal Nature Communications on Sept. 1, 2025.
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Last Updated Sep 02, 2025 Related Terms
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By European Space Agency
The European Space Agency-led Solar Orbiter mission has split the flood of energetic particles flung out into space from the Sun into two groups, tracing each back to a different kind of outburst from our star.
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By NASA
5 min read
Close-Up Views of NASA’s DART Impact to Inform Planetary Defense
Photos taken by the Italian LICIACube, short for the LICIA Cubesat for Imaging of Asteroids. These offer the closest, most detailed observations of NASA’s DART (Double Asteroid Redirection Test) impact aftermath to date. The photo on the left was taken roughly 2 minutes and 40 seconds after impact, as the satellite flew past the Didymos system. The photo on the right was taken 20 seconds later, as LICIACube was leaving the scene. The larger body, near the top of each image is Didymos. The smaller body in the lower half of each image is Dimorphos, enveloped by the cloud of rocky debris created by DART’s impact. NASA/ASI/University of Maryland On Sept. 11, 2022, engineers at a flight control center in Turin, Italy, sent a radio signal into deep space. Its destination was NASA’s DART (Double Asteroid Redirection Test) spacecraft flying toward an asteroid more than 5 million miles away.
The message prompted the spacecraft to execute a series of pre-programmed commands that caused a small, shoebox-sized satellite contributed by the Italian Space Agency (ASI), called LICIACube, to detach from DART.
Fifteen days later, when DART’s journey ended in an intentional head-on collision with near-Earth asteroid Dimorphos, LICIACube flew past the asteroid to snap a series of photos, providing researchers with the only on-site observations of the world’s first demonstration of an asteroid deflection.
After analyzing LICIACube’s images, NASA and ASI scientists report on Aug. 21 in the Planetary Science Journal that an estimated 35.3 million pounds (16 million kilograms) of dust and rocks spewed from the asteroid as a result of the crash, refining previous estimates that were based on data from ground and space-based observations.
While the debris shed from the asteroid amounted to less than 0.5% of its total mass, it was still 30,000 times greater than the mass of the spacecraft. The impact of the debris on Dimorphos’ trajectory was dramatic: shortly after the collision, the DART team determined that the flying rubble gave Dimorphos a shove several times stronger than the hit from the spacecraft itself.
“The plume of material released from the asteroid was like a short burst from a rocket engine,” said Ramin Lolachi, a research scientist who led the study from NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The important takeaway from the DART mission is that a small, lightweight spacecraft can dramatically alter the path of an asteroid of similar size and composition to Dimorphos, which is a “rubble-pile” asteroid — or a loose, porous collection of rocky material bound together weakly by gravity.
“We expect that a lot of near-Earth asteroids have a similar structure to Dimorphos,” said Dave Glenar, a planetary scientist at the University of Maryland, Baltimore County, who participated in the study. “So, this extra push from the debris plume is critical to consider when building future spacecraft to deflect asteroids from Earth.”
The tail of material that formed behind Dimorphos was prominent almost 12 days after the DART impact, giving the asteroid a comet-like appearance, as seen in this image captured by NASA’s Hubble Space Telescope in October 2022. Hubble’s observations were made from roughly 6.8 million miles away. NASA, ESA, STScI, Jian-Yang Li (PSI); Image Processing: Joseph DePasquale DART’s Star Witness
NASA chose Dimorphos, which poses no threat to Earth, as the mission target due to its relationship with another, larger asteroid named Didymos. Dimorphos orbits Didymos in a binary asteroid system, much like the Moon orbits Earth. Critically, the pair’s position relative to Earth allowed astronomers to measure the duration of the moonlet’s orbit before and after the collision.
Ground and space-based observations revealed that DART shortened Dimorphos’ orbit by 33 minutes. But these long-range observations, made from 6.8 million miles (10.9 million kilometers) away, were too distant to support a detailed study of the impact debris. That was LICIACube’s job.
After DART’s impact, LICIACube had just 60 seconds to make its most critical observations. Barreling past the asteroid at 15,000 miles (21,140 kilometers) per hour, the spacecraft took a snapshot of the debris roughly once every three seconds. Its closest image was taken just 53 miles (85.3 km) from Dimorphos’ surface.
The short distance between LICIACube and Dimorphos provided a unique advantage, allowing the cubesat to capture detailed images of the dusty debris from multiple angles.
The research team studied a series of 18 LICIAcube images. The first images in the sequence showed LICIACube’s head-on approach. From this angle, the plume was brightly illuminated by direct sunlight. As the spacecraft glided past the asteroid, its camera pivoted to keep the plume in view.
This animated series of images was taken by a camera aboard LICIACube 2 to 3 minutes after DART crashed into Dimorphos. As LICIACube made its way past the binary pair of asteroids Didymos, the larger one on top, and Dimorphos, the object at the bottom. The satellite’s viewing angle changed rapidly during its flyby of Dimorphos, allowing scientists o get a comprehensive view of the impact plume from a series of angles. ASI/University of Maryland/Tony Farnham/Nathan Marder As LICIACube looked back at the asteroid, sunlight filtered through the dense cloud of debris, and the plume’s brightness faded. This suggested the plume was made of mostly large particles — about a millimeter or more across — which reflect less light than tiny dust grains.
Since the innermost parts of the plume were so thick with debris that they were completely opaque, the scientists used models to estimate the number of particles that were hidden from view. Data from other rubble-pile asteroids, including pieces of Bennu delivered to Earth in 2023 by NASA’s OSIRIS-REx spacecraft, and laboratory experiments helped refine the estimate.
“We estimated that this hidden material accounted for almost 45% of the plume’s total mass,” said Timothy Stubbs, a planetary scientist at NASA Goddard who was involved with the study.
While DART showed that a high-speed collision with a spacecraft can change an asteroid’s trajectory, Stubbs and his colleagues note that different asteroid types, such as those made of stronger, more tightly packed material, might respond differently to a DART-like impact. “Every time we interact with an asteroid, we find something that surprises us, so there’s a lot more work to do,” said Stubbs. “But DART is a big step forward for planetary defense.”
The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, managed the DART mission and operated the spacecraft for NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office.
By Nathan Marder, nathan.marder@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Aug 21, 2025 Related Terms
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By NASA
A collaboration between NASA and the small business Aloft Sensing produced a new compact radar system that will enable researchers to leverage High Altitude Long Endurance (HALE) platforms to observe dynamic Earth systems. This new radar is small, provides highly sensitive measurements, and doesn’t require GPS for positioning; eventually, it could be used on vehicles in space.
HALE InSAR flies aboard a high-altitude balloon during a test-flight. This lightweight instrument will help researchers measure ground deformation and dynamic Earth systems. Credit: Aloft Sensing Long before a volcano erupts or a mountainous snowpack disappears, millimeter-scale changes in Earth’s surface indicate larger geologic processes are at work. But detecting those minute changes, which can serve as early warnings for impending disasters, is difficult.
With support from NASA’s Earth Science Technology Office (ESTO ) a team of researchers from the small aerospace company Aloft Sensing is developing a compact radar instrument for observing Earth’s surface deformation, topography, and vegetation with unprecedented precision.
Their project, “HALE InSAR,” has demonstrated the feasibility of using high-altitude, long-endurance (HALE) vehicles equipped with Interferometric Synthetic Aperture Radar (InSAR) to observe changes in surface deformation mere millimeters in size and terrain information with centimetric vertical accuracy.
“It’s a level of sensitivity that has eluded traditional radar sensors, without making them bulky and expensive,” said Lauren Wye, CEO of Aloft Sensing and principal investigator for HALE InSAR.
HALE vehicles are lightweight aircraft designed to stay airborne for extended periods of time, from weeks to months and even years. These vehicles can revisit a scene multiple times an hour, making them ideal for locating subtle changes in an area’s geologic environment.
InSAR, a remote sensing technique that compares multiple images of the same scene to detect changes in surface topography or determine structure, is also uniquely well-suited to locate these clues. But traditional InSAR instruments are typically too large to fly aboard HALE vehicles.
HALE InSAR is different. The instrument is compact enough for a variety of HALE vehicles, weighing less than 15 pounds (seven kilograms) and consuming fewer than 300 watts of power, about as much energy as it takes to power an electric bike.
HALE InSAR leverages previously-funded NASA technologies to make such detailed measurements from a small platform: a novel electronically steered antenna and advanced positioning algorithms embedded within an agile software-defined transceiver. These technologies were developed under ESTO’s Instrument Incubation Program (IIP) and Decadal Survey Incubation (DSI) Program, respectively.
“All of the design features that we’ve built into the instrument are starting to showcase themselves and highlight why this payload in particular is distinct from what other small radars might be looking to achieve,” said Wye.
One of those features is a flat phased array antenna, which gives users the ability to focus HALE InSAR’s radar beam without physically moving the instrument. Using a panel about the size of a tablet computer, operators can steer the beam electronically, eliminating the need for gimbles and other heavy components, which helps enable the instrument’s reduced size and weight.
A close up HALE InSAR fixed to a high-altitude airship. The flat planar antenna reduces the instruments mass and eliminates the need for gimbles and other heavy components. Credit: Aloft Sensing “SAR needs to look to the side. Our instrument can be mounted straight down, but look left and right on every other pulse such that we’re collecting a left-looking SAR image and a right-looking SAR image essentially simultaneously. It opens up opportunities for the most mass-constrained types of stratospheric vehicles,” said Wye.
Using advanced positioning algorithms, HALE InSAR also has the unique ability to locate itself without GPS, relying instead on feedback from its own radar signals to determine its position even more accurately. Brian Pollard, Chief Engineer at Aloft Sensing and co-investigator for HALE InSAR, explained that precise positioning is essential for creating high-resolution data about surface deformation and topography.
“SAR is like a long exposure camera, except with radio waves. Your exposure time could be a minute or two long, so you can imagine how much smearing goes on if you don’t know exactly where the radar is,” said Pollard.
Navigating without GPS also makes HALE InSAR ideal for field missions in austere environments where reliable GPS signals may be unavailable, increasing the instrument’s utility for national security applications and science missions in remote locations.
The Aloft Sensing team recently achieved several key milestones, validating their instrument aboard an airship at 65,000 feet as well as small stratospheric balloons. Next, they’ll test HALE InSAR aboard a fixed wing HALE aircraft. A future version of their instrument could even find its way into low Earth orbit on a small satellite.
Wye credits NASA support for helping her company turn a prototype into a proven instrument.
“This technology has been critically enabled by ESTO, and the benefit to science and civil applications is huge,” said Wye. “It also exemplifies the dual-use potential enabled by NASA-funded research. We are seeing significant military interest in this capability now that it is reaching maturity. As a small business, we need this hand-in-hand approach to be able to succeed.”
For more information about opportunities to work with NASA to develop new Earth observation technologies, visit esto.nasa.gov.
For additional details, see the entry for this project on NASA TechPort.
Project Lead: Dr. Lauren Wye, CEO, Aloft Sensing
Sponsoring Organization: NASA’s Instrument Incubation Program (IIP)
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Last Updated Aug 19, 2025 Related Terms
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