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By NASA
A scanning electron microscope image of a micrometeorite impact crater in a particle of asteroid Bennu material. Credits: NASA/Zia Rahman 5 min read
NASA’s Bennu Samples Reveal Complex Origins, Dramatic Transformation
Asteroid Bennu, sampled by NASA’s OSIRIS-REx mission in 2023, is a mixture of dust that formed in our solar system, organic matter from interstellar space, and pre-solar system stardust. Its unique and varied contents were dramatically transformed over time by interactions with water and exposure to the harsh space environment.
These insights come from a trio of newly published papers based on the analysis of Bennu samples by scientists at NASA and other institutions.
Bennu is made of fragments from a larger parent asteroid destroyed by a collision in the asteroid belt, between the orbits of Mars and Jupiter. One of the papers, co-led by Jessica Barnes at the University of Arizona, Tucson, and Ann Nguyen of NASA’s Johnson Space Center in Houston and published in the journal Nature Astronomy, suggests that Bennu’s ancestor was made up of material that had diverse origins—near the Sun, far from the Sun, and even beyond our solar system.
The analyses show that some of the materials in the parent asteroid, despite very low odds, escaped various chemical processes driven by heat and water and even survived the extremely energetic collision that broke it apart and formed Bennu.
“We traced the origins of these initial materials accumulated by Bennu’s ancestor,” said Nguyen. “We found stardust grains with compositions that predate the solar system, organic matter that likely formed in interstellar space, and high temperature minerals that formed closer to the Sun. All of these constituents were transported great distances to the region that Bennu’s parent asteroid formed.”
The chemical and atomic similarities of samples from Bennu, the asteroid Ryugu (sampled by JAXA’s (the Japan Aerospace Exploration Agency) Hayabusa2 mission) and the most chemically primitive meteorites collected on Earth suggest their parent asteroids may have formed in a similar, distant region of the early solar system. Yet the differences from Ryugu and meteorites that were seen in the Bennu samples may indicate that this region changed over time or did not mix as well as some scientists have thought.
We found stardust grains with compositions that predate the solar system, organic matter that likely formed in interstellar space, and high temperature minerals that formed closer to the Sun.
Ann Nguyen
Planetary Scientist
Though some original constituents survived, most of Bennu’s materials were transformed by reactions with water, as reported in the paper co-led by Tom Zega of the University of Arizona and Tim McCoy of the Smithsonian’s National Museum of Natural History in Washington and published in Nature Geoscience. In fact, minerals in the parent asteroid likely formed, dissolved, and reformed over time.
“Bennu’s parent asteroid accumulated ice and dust. Eventually that ice melted, and the resulting liquid reacted with the dust to form what we see today, a sample that is 80% minerals that contain water,” said Zega. “We think the parent asteroid accumulated a lot of icy material from the outer solar system, and then all it needed was a little bit of heat to melt the ice and cause liquids to react with solids.”
Bennu’s transformation did not end there. The third paper, co-led by Lindsay Keller at NASA Johnson and Michelle Thompson of Purdue University, also published in Nature Geoscience, found microscopic craters and tiny splashes of once-molten rock – known as impact melts – on the sample surfaces, signs that the asteroid was bombarded by micrometeorites. These impacts, together with the effects of solar wind, are known as space weathering and occurred because Bennu has no atmosphere to protect it.
“The surface weathering at Bennu is happening a lot faster than conventional wisdom would have it, and the impact melt mechanism appears to dominate, contrary to what we originally thought,” said Keller. “Space weathering is an important process that affects all asteroids, and with returned samples, we can tease out the properties controlling it and use that data and extrapolate it to explain the surface and evolution of asteroid bodies that we haven’t visited.”
Ann Nguyen, co-lead author of a new paper that gives insights into the diverse origin of asteroid Bennu’s “parent” asteroid works alongside the NanoSIMS 50L (nanoscale secondary ion mass spectrometry) ion microprobe in the Astromaterials Research and Exploration Science Division at NASA’s Johnson Space Center in Houston. Credit: NASA/James Blair As the leftover materials from planetary formation 4.5 billion years ago, asteroids provide a record of the solar system’s history. But as Zega noted, we’re seeing that some of these remnants differ from what has been found in meteorites on Earth, because certain types of asteroids burn up in the atmosphere and never make it to the ground. That, the researchers point out, is why collecting actual samples is so important.
“The samples are really crucial for this work,” Barnes said. “We could only get the answers we got because of the samples. It’s super exciting that we’re finally able to see these things about an asteroid that we’ve been dreaming of going to for so long.”
The next samples NASA expects to help unravel our solar system’s story will be Moon rocks returned by the Artemis III astronauts.
NASA’s Goddard Space Flight Center provided overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator. The university leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft and provided flight operations. Goddard and KinetX Aerospace were responsible for navigating the OSIRIS-REx spacecraft. Curation for OSIRIS-REx takes place at NASA’s Johnson Space Center in Houston. International partnerships on this mission include the OSIRIS-REx Laser Altimeter instrument from the Canadian Space Agency and asteroid sample science collaboration with JAXA’s Hayabusa2 mission. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.
Melissa Gaskill
Johnson Space Center
For more information on NASA’s OSIRIS-REx mission, visit:
https://science.nasa.gov/mission/osiris-rex/
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Victoria Segovia
Johnson Space Center
(281) 483-5111
victoria.segovia@nasa.gov
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
This artist’s concept shows the Moon’s hot interior and volcanism about 2 to 3 billion years ago. It is thought that volcanic activity on the lunar near side (the side facing Earth) helped create a landscape dominated by vast plains called mare, which are formed by molten rock that cooled and solidified. NASA/JPL-Caltech Analyzing gravity data collected by spacecraft orbiting other worlds reveals groundbreaking insights about planetary structures without having to land on the surface.
Although the Moon and the asteroid Vesta are very different, two NASA studies use the same technique to reveal new details about the interiors of both.
In the lunar study, published May 14 in the journal Nature, researchers developed a new gravity model of the Moon that includes tiny variations in the celestial body’s gravity during its elliptical orbit around Earth. These fluctuations cause the Moon to flex slightly due to Earth’s tidal force — a process called tidal deformation — which provides critical insights into the Moon’s deep internal structure.
Using their model, the researchers produced the most detailed lunar gravitational map yet, providing future missions an improved way to calculate location and time on the Moon. They accomplished this by analyzing data on the motion of NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission, whose spacecraft, Ebb and Flow, orbited the Moon from Dec. 31, 2011, to Dec. 17, 2012.
These views of the Moon’s near side, left, and far side were put together from observations made by NASA’s Lunar Reconnaissance Orbiter. NASA/JPL-Caltech In a second study, published in the journal Nature Astronomy on April 23, the researchers focused on Vesta, an object in the main asteroid belt between Mars and Jupiter. Using NASA’s Deep Space Network radiometric data and imaging data from the agency’s Dawn spacecraft, which orbited the asteroid from July 16, 2011, to Sept. 5, 2012, they found that instead of having distinct layers as expected, Vesta’s internal structure may be mostly uniform, with a very small iron core or no core at all.
“Gravity is a unique and fundamental property of a planetary body that can be used to explore its deep interior,” said Park. “Our technique doesn’t need data from the surface; we just need to track the motion of the spacecraft very precisely to get a global view of what’s inside.”
Lunar Asymmetry
The lunar study looked at gravitational changes to the Moon’s near and far sides. While the near side is dominated by vast plains — known as mare — formed by molten rock that cooled and solidified billions of years ago, the far side is more rugged, with few plains.
NASA’s Dawn mission obtained this image of the giant asteroid Vesta on July 24, 2011. The spacecraft spent 14 months orbiting the asteroid, capturing more than 30,000 images and fully mapping its surface. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA Both studies were led by Ryan Park, supervisor of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory in Southern California, and were years in the making due to their complexity. The team used NASA supercomputers to build a detailed map of how gravity varies across each body. From that, they could better understand what the Moon and Vesta are made of and how planetary bodies across the solar system formed.
Some theories suggest intense volcanism on the near side likely caused these differences. That process would have caused radioactive, heat-generating elements to accumulate deep inside the near side’s mantle, and the new study offers the strongest evidence yet that this is likely the case.
“We found that the Moon’s near side is flexing more than the far side, meaning there’s something fundamentally different about the internal structure of the Moon’s near side compared to its far side,” said Park. “When we first analyzed the data, we were so surprised by the result we didn’t believe it. So we ran the calculations many times to verify the findings. In all, this is a decade of work.”
When comparing their results with other models, Park’s team found a small but greater-than-expected difference in how much the two hemispheres deform. The most likely explanation is that the near side has a warm mantle region, indicating the presence of heat-generating radioactive elements, which is evidence for volcanic activity that shaped the Moon’s near side 2 billion to 3 billion years ago.
Vesta’s Evolution
Park’s team applied a similar approach for their study that focused on Vesta’s rotational properties to learn more about its interior.
“Our technique is sensitive to any changes in the gravitational field of a body in space, whether that gravitational field changes over time, like the tidal flexing of the Moon, or through space, like a wobbling asteroid,” said Park. “Vesta wobbles as it spins, so we could measure its moment of inertia, a characteristic that is highly sensitive to the internal structure of the asteroid.”
Changes in inertia can be seen when an ice skater spins with their arms held outward. As they pull their arms in, bringing more mass toward their center of gravity, their inertia decreases and their spin speeds up. By measuring Vesta’s inertia, scientists can gain a detailed understanding of the distribution of mass inside the asteroid: If its inertia is low, there would be a concentration of mass toward its center; if it’s high, the mass would be more evenly distributed.
Some theories suggest that over a long period, Vesta gradually formed onion-like layers and a dense core. But the new inertia measurement from Park’s team suggests instead that Vesta is far more homogeneous, with its mass distributed evenly throughout and only a small core of dense material, or no core.
Gravity slowly pulls the heaviest elements to a planet’s center over time, which is how Earth ended up with a dense core of liquid iron. While Vesta has long been considered a differentiated asteroid, a more homogenous structure would suggest that it may not have fully formed layers or may have formed from the debris of another planetary body after a massive impact.
In 2016, Park used the same data types as the Vesta study to focus on Dawn’s second target, the dwarf planet Ceres, and results suggested a partially differentiated interior.
Park and his team recently applied a similar technique to Jupiter’s volcanic moon Io, using data acquired by NASA’s Juno and Galileo spacecraft during their flybys of the Jovian satellite as well as from ground-based observations. By measuring how Io’s gravity changes as it orbits Jupiter, which exerts a powerful tidal force, they revealed that the fiery moon is unlikely to possess a global magma ocean.
“Our technique isn’t restricted just to Io, Ceres, Vesta, or the Moon,” said Park. “There are many opportunities in the future to apply our technique for studying the interiors of intriguing planetary bodies throughout the solar system.”
News Media Contacts
Ian J. O’Neill
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649
ian.j.oneill@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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Last Updated May 14, 2025 Related Terms
Vesta Dawn Earth's Moon GRAIL (Gravity Recovery And Interior Laboratory) Jet Propulsion Laboratory Planetary Science Small Bodies of the Solar System The Solar System Explore More
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By NASA
In about 5 billion years, our Sun will run out of fuel and expand, possibly engulfing Earth. These end stages of a star’s life can be utterly beautiful – as is the case with this planetary nebula called the Helix Nebula. Astronomers study these objects by looking at all kinds of light.X-ray: NASA/CXC/SAO/Univ Mexico/S. Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optical: NASA/ESA/STScI (M. Meixner)/NRAO (T.A. Rector); Infrared: ESO/VISTA/J. Emerson; Image Processing: NASA/CXC/SAO/K. Arcand This image of the Helix Nebula, released on March 4, 2025, shows a potentially destructive white dwarf at the nebula’s center: this star may have destroyed a planet. This has never been seen before – and could explain a mysterious X-ray signal that astronomers have detected from the nebula for over 40 years.
This view combines X-rays from NASA’s Chandra X-ray Observatory (magenta), optical light data from NASA’s Hubble Space Telescope (orange, light blue), infrared data from the European Southern Observatory VISTA telescope (gold, dark blue), and ultraviolet data from GALEX (purple) of the Helix Nebula. Data from Chandra indicates that this white dwarf has destroyed a very closely orbiting planet.
Image credit: X-ray: NASA/CXC/SAO/Univ Mexico/S. Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optical: NASA/ESA/STScI (M. Meixner)/NRAO (T.A. Rector); Infrared: ESO/VISTA/J. Emerson; Image Processing: NASA/CXC/SAO/K. Arcand
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By European Space Agency
The European Space Agency is releasing the first catalogue of astronomical data from the Euclid space telescope, including three new enormous image mosaics with zoom-ins. Follow the reveal live on Wednesday 19 March at 11:00 BST / 12:00 CET.
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