SPACE/COSMOS
Asteroid Bennu is a time capsule of materials bearing witness to its origin and transformation over billions of years
Three publications by members of the UA-led OSIRIS-REx sample analysis team reveal the asteroid's composition and history in unprecedented detail
University of Arizona
image:
Jessica Barnes examines a vial containing sample particles at the Kuiper-Arizona Laboratory for Astromaterials Analysis, located at the University of Arizona.
view moreCredit: Chris Richards, University of Arizona
Asteroid Bennu — the target of NASA's OSIRIS-REx sample return mission, led by the University of Arizona — is a mixture of materials from throughout, and even beyond, our solar system. Over the past few billion years, its unique and varied contents have been transformed by interactions with water and the harsh space environment.
These details come from a trio of newly published papers based on analysis of Bennu samples delivered to Earth by OSIRIS-REx in 2023. The OSIRIS-REx sample analysis campaign is coordinated by the U of A's Lunar and Planetary Laboratory (LPL) and involves scientists from around the world. LPL researchers contributed to all three studies and led two of them.
"This is work you just can’t do with telescopes," said Jessica Barnes, associate professor at the U of A's Lunar and Planetary Laboratory and co-lead author on one of the publications. "It's super exciting that we're finally able to say these things about an asteroid that we've been dreaming of going to for so long and eventually brought back samples from."
Bennu is made of fragments from a larger "parent" asteroid that broke up after it collided with another asteroid, likely in the asteroid belt between the orbits of Mars and Jupiter. The parent asteroid consisted of material with diverse origins — near the sun, far from the sun, and from other stars — that coalesced more than 4 billion years ago as our solar system was forming. These findings are the subject of the first paper, published in Nature Astronomy and jointly led by Barnes and Ann Nguyen with the Astromaterials Research and Exploration Science Division at NASA’s Johnson Space Center in Houston.
"Bennu's parent asteroid may have formed in the outer parts of the solar system, possibly beyond the giant planets, Jupiter and Saturn," Barnes said. "We think this parent body was struck by an incoming asteroid and smashed apart. Then the fragments re-assembled and this might have repeated several times."
By looking at the samples returned by the OSIRIS-REx spacecraft, Barnes and her colleagues were able to get the most comprehensive snapshot of its history to date. Among the findings was an abundance of stardust, material that existed before our solar system formed, Barnes said. The discovery of these most ancient materials was made possible, in part, by the NanoSIMS instrument at the U of A's Kuiper-Arizona Laboratory for Astromaterials Analysis, which can reveal a sample's isotopes — variants of chemical elements — at nanometer scales. The tiny grains of stardust are identifiable by their unusual isotopic makeup compared to materials formed in the solar system.
"Those are pieces of stardust from other stars that are long dead, and these pieces were incorporated into the cloud of gas and dust from which our solar system formed," Barnes said. "In addition, we found organic material that's highly anomalous in their isotopes and that was probably formed in interstellar space, and we have solids that formed closer to the sun, and for the first time, we show that all these materials are present in Bennu."
The chemical and isotopic similarities between samples from Bennu and a similar asteroid, Ryugu, which was sampled by the Japanese Hayabusa 2 mission in 2019, and the most chemically primitive meteorites found on Earth suggest their parent asteroids may have formed in a shared region of the early solar system. Yet the differences researchers are observing in the Bennu samples may indicate that the starting materials in this region changed over time or were not as well-mixed as some scientists have thought.
The analyses show that some of the materials in the parent asteroid survived various chemical processes involving heat and water and even the energetic collision that resulted in the formation of Bennu. Nevertheless, most of the materials were transformed by hydrothermal processes, as reported in the second paper, published in Nature Geoscience. In fact, that study found, minerals in the parent asteroid likely formed, dissolved and reformed over time due to interactions with water.
"We think that Bennu’s parent asteroid accreted a lot of icy material from the outer solar system, which melted over time," said Tom Zega, director of the Kuiper-Arizona Laboratory who co-led the study with Tim McCoy, curator of meteorites at the Smithsonian.
The team found evidence that silicate minerals would have reacted with the resultant liquid water at relatively low temperatures of about 25 degrees Celsius, or room temperature. That heat could have either lingered from the accretion process itself, when Bennu's parent asteroid first formed, or was generated by impacts later in its history, possibly in combination with the decay of radioactive elements deep inside it. The trapped heat could have melted the ice inside the asteroid, according to Zega.
"Now you have a liquid in contact with a solid and heat — everything you need to start doing chemistry," he said. "The water reacted with the minerals and formed what we see today: samples in which 80% of minerals contain water in their interior, created billions of years ago when the solar system was still forming."
The transformation of Bennu's materials did not end there. The third paper, also published in Nature Geoscience, reports microscopic craters and tiny splashes of once-molten rock on the surfaces of Bennu particles — signs that the asteroid has been peppered by micrometeorite impacts. These impacts, together with the effects of solar wind, are known as "space weathering" and occur because Bennu does not have an atmosphere to protect it. This weathering is happening a lot faster than conventional wisdom would have it, according to the study, which was led by Lindsay Keller at NASA Johnson and Michelle Thompson at Purdue University.
As the leftover materials from planetary formation 4.5 billion years ago, asteroids provide a record of the solar system’s history. But many of these remnants may be different from what meteorites recovered on Earth would suggest, Zega said, because different types of meteors (fragments of asteroids) may burn up in the atmosphere and never make it to the ground.
"And those that do make it to the ground can react with Earth’s atmosphere, particularly if the meteorite is not recovered quickly after it falls," he added, "which is why sample return missions such as OSIRIS-REx are critical."
Journal
Nature Astronomy
A scanning electron microscope image of a micrometeorite impact crater in a particle of asteroid Bennu material.
Jessica Barnes working in the Kuiper-Arizona Laboratory for Astromaterials Analysis at the University of Arizona.
Credit
Chris Richards, University of Arizona
Tom Zega leads the Kuiper-Arizona Laboratory at the University of Arizona
Credit
Arlene Islas, University of Arizona
‘Root beer FLOAT’ burst’s home is located with extraordinary precision
New Outrigger system traces the cosmic flash to a nearby galaxy’s single spiral arm
Northwestern University
image:
Artistic interpretation of CHIME's Outrigger array over North America localizing RBFLOAT to its host galaxy.
view moreCredit: Daniëlle Futselaar/MMT Observatory
An international team of scientists, including Northwestern University astrophysicists, has spotted one of the brightest fast radio bursts (FRBs) ever recorded — and pinpointed its location with unprecedented precision.
The millisecond-long blast — nicknamed RBFLOAT (short for “radio-brightest flash of all time” and, yes, a nod to “root beer float”) — was discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and its newly completed “Outrigger” array. By combining observations from sites in British Columbia, West Virginia and California, scientists traced the burst to a single spiral arm of a galaxy 130 million light-years away — accurate within just 42 light-years.
Because they occur so far away and vanish within the blink of an eye, FRBs are notoriously difficult to study. If scientists can pinpoint an FRB’s exact location, however, they can explore its environment, including characteristics of its home galaxy, distance from Earth and potentially even its cause. Eventually, this information could help shed light on the nature and origins of these mysterious, fleeting bursts.
The study will be published on Thursday (Aug. 21) in The Astrophysical Journal Letters. It marks the first time the full Outrigger array was used to localize an FRB.
“It is remarkable that only a couple of months after the full Outrigger array went online, we discovered an extremely bright FRB in a galaxy in our own cosmic neighborhood,” said Northwestern’s Wen-fai Fong, a senior author on the study. “This bodes very well for the future. An increase in event rates always provides the opportunity for discovering more rare events. The CHIME/FRB collaboration worked for many years toward this technical achievement, and the universe rewarded us with an absolute gift.”
“This result marks a turning point,” said corresponding author Amanda Cook, a postdoctoral researcher at McGill University. “Instead of just detecting these mysterious flashes, we can now see exactly where they are coming from. It opens the door for discovering whether they are caused by dying stars, exotic magnetic objects or something we haven’t even thought of yet.”
An expert on cosmic explosions, Fong is an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences. She also is a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and the NSF-Simons AI Institute for the Sky (SkAI Institute).
Four days of solar energy packed into a single blink
Flaring up and disappearing within milliseconds, FRBs are brief, powerful radio blasts that generate more energy in one quick burst than our sun emits in an entire year. While most pass unnoticed, every once in a while, an FRB is bright enough to detect. FRB20250316A, or RBFLOAT, was one of these rare events. Detected in March 2025, RBFLOAT released as much energy in a few milliseconds as the sun produces in four days.
“It was so bright that our pipeline initially flagged it as radio frequency interference, signals often caused by cell phones or airplanes that are much closer to home,” Fong said. “It took some sleuthing by members of our collaboration to uncover that it was a real astrophysical signal.”
And while many FRBs repeat — pulsing multiple times across several months — RBFLOAT emitted all its energy in just one burst. Even in the hundreds of hours after it was first observed, astronomers did not detect repeat bursts from the source. That means astrophysicists couldn’t wait for another flare to gather more data. Instead, they only had one shot at pinpointing its location.
“RBFLOAT was the first non-repeating source localized to such precision,” said Northwestern’s Sunil Simha, a postdoctoral scholar at CIERA and study co-author. “These are much harder to locate. Thus, even detecting RBFLOAT is proof of concept that CHIME is indeed capable of detecting such events and building a statistically interesting sample of FRBs.”
FRB forensics hint at a magnetar
To investigate RBFLOAT’s origin, the scientists relied on CHIME, a large radio telescope in British Columbia and the world’s most prolific FRB hunter. Smaller versions of CHIME, the Outriggers enable astronomers to triangulate signals to precisely confine the specific locations of FRBs on the sky.
With this array of vantage points, the team traced the burst to the Big Dipper constellation in the outskirts of a galaxy about 130 million light-years away from Earth. The team precisely pinpointed it to a region just 45 light-years across, which is smaller than an average star cluster.
Follow-up observations from the 6.5-meter MMT telescope in Arizona and the Keck Cosmic Web Imager on the 10-meter Keck II Telescope in Hawai‘i provided the most detailed view yet of a non-repeating FRB’s surroundings. Simha analyzed the optical data obtained from Keck, and Northwestern graduate student Yuxin “Vic” Dong used the MMT to obtain deep optical images of the FRB’s host galaxy.
Their investigations revealed the burst occurred along a spiral arm of the galaxy, which is dotted with many star-forming regions. The RBFLOAT occurred near, but not inside, one of these star-forming regions. Although astrophysicists still don’t know exactly what causes FRBs, this evidence bolsters one leading hypothesis. At least some appear to come from magnetars, ultra-magnetized neutron stars born from the deaths of massive stars. Star-forming regions often host young magnetars, which are energetic enough to produce quick, powerful bursts.
“We found the FRB lies at the outskirts of a star-forming region that hosts massive stars,” Simha said. “For the first time, we could even estimate how deeply it’s embedded in surrounding gas, and it’s relatively shallow.”
Keck’s rich dataset and FRB’s precise location enabled the team to perform first-of-its-kind analysis of the galaxy’s properties at the FRB’s location. These uncovered characteristics include the density of the galaxy’s gas, star-formation rate and presence of elements heavier than hydrogen and helium.
“The FRB lies on a spiral arm of its host galaxy,” added Dong, who is the principal investigator of the MMT program. “Spiral arms are typically sites of ongoing star formation, which supports the idea that it came from a magnetar. Using our extremely sensitive MMT image, we were able to zoom in further and found that the FRB is actually outside the nearest star-forming clump. This location is intriguing because we would expect it to be located within the clump, where star formation is happening. This could suggest that the progenitor magnetar was kicked from its birth site or that it was born right at the FRB site and away from the clump’s center.”
The start of something spectacular
With the CHIME Outriggers now fully running, astronomers expect to pin down hundreds more FRBs each year — bringing them closer than ever to solving the mystery of what causes these spectacular flashes. The localization power of the Outriggers, combined with CHIME’s wide field of view, marks a turning point for the FRB search.
“For years, we’ve known FRBs occur all over the sky, but pinning them down has been painstakingly slow,” Dong said. “Now, we can routinely tie them to specific galaxies, even down to neighborhoods within those galaxies.”
“The entire FRB community has only published about 100 well-localized events in the past eight years,” Simha said. “Now, we expect more than 200 precise detections per year from CHIME alone. RBFLOAT was a spectacular source to begin building such a sample.”
"Thanks to the CHIME Outriggers, we're now entering a new era of FRB science,” said study co-author Tarraneh Eftekhari, who is CIERA’s assistant director. “With hundreds of precisely localized events expected in the next few years, we can start to understand the full breadth of environments from which these mysterious signals emanate, bringing us one step closer to unlocking their secrets. RBFLOAT is just the beginning."
The study, “FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 parsec Precision,” was supported by the National Science Foundation, the David and Lucile Packard Foundation, the Alfred P. Sloan Foundation, the Research Corporation of Science Advancement, the Gordon & Betty Moore Foundation, the Canadian Institute for Advanced Research, the Canadian Natural Sciences and Engineering Council of Canada, the Canada Foundation for Innovation and the Trottier Space Institute at McGill. The CHIME collaboration includes astrophysicists from Northwestern, McGill University, the Massachusetts Institute of Technology, University of Toronto, University of British Columbia and several other institutions.
Journal
The Astrophysical Journal Letters
Method of Research
Observational study
Article Title
FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 parsec Precision
Article Publication Date
21-Aug-2025
Location of RBFLOAT next to its host galaxy.
Credit
Yuxin "Vic" Dong/MMT
Dusty structure explains near vanishing of faraway star
Newfound binary system is a cosmic oddball, researchers say
Ohio State University
COLUMBUS, Ohio – Stars die and vanish from sight all the time, but astronomers were puzzled when one that had been stable for more than a decade almost disappeared for eight months.
Between late 2024 and early 2025, one star in our galaxy, dubbed ASASSN-24fw, dimmed in brightness by about 97%, before brightening again. Since then, scientists have been swapping theories about what was behind this rare, exciting event.
Now, an international team led by scientists at The Ohio State University may have come up with an answer to the mystery. In a new study recently published in The Open Journal of Astrophysics, astronomers suggest that because the color of the star’s light remained unchanged during its dimming, the event wasn’t caused by the star evolving in some way, but by a large cloud of dust and gas around the star that occluded Earth’s view of it.
“We explored three different scenarios for what could be going on,” said Raquel Forés-Toribio, lead author of the study and a postdoctoral researcher in astronomy at Ohio State. “Evidence suggests it is likely that there is a cloud of dust in the form of a disk around it.”
ASASSN-24fw is an F-type star — a star that is a little more massive than our sun and about twice as big — and is located about 3,000 light-years away from Earth. Researchers estimate that the cloudy disk it’s surrounded by is about 1.3 astronomical units (AU) across, even bigger than the distance between the sun and our planet. (One AU is the distance between the center of the Earth and the center of the sun.)
Researchers suggest this disk is also likely made up of large clusters of carbon or water ice close in size to a large grain of dust found on Earth. This material is similar enough to planet-forming disks that studying it could give astronomers novel insights into stellar formation and evolution.
Yet these findings alone don’t explain all of the system’s abnormalities, said Forés-Toribio. Instead, researchers think that a smaller, cooler star may also orbit ASASSN-24fw, which would make it a hidden binary system.
“At this moment, with the data that we have, what we propose is that there should be two stars together in a binary system,” said Forés-Toribio. “The second star, which is much fainter and less massive, may be driving the changes in geometry leading to the eclipses.”
While dimming systems like the one the team saw are rare, this one-in-a-million eclipsing was especially dramatic, said Chris Kochanek, co-author of the study and a professor of astronomy at Ohio State, as even when researchers searched for similar objects, they couldn’t find one that fit the same exact pattern.
“We were hoping to find some similarities and we didn’t really find very many, which is interesting in and of itself,” said Kochanek. “But the hope is, as we find more in the future, some patterns might eventually be revealed.”
The system was discovered as part of the All-Sky Automated Survey for Supernovae (ASAS-SN) project, a network of small telescopes that monitor the entire visible night sky. Since its establishment more than a decade ago, ASAS-SN has collected about 14 million images and counting of the cosmos.
“The universe’s capacity to surprise us is continuous,” said Krzysztof Stanek, another co-author of the study and a professor of astronomy at Ohio State. “Even with small telescopes on the ground and big telescopes in space, every time we get a new capability, we still discover new things.”
According to the team, the ASASSN-24fw system likely experiences an eclipse about once every 43.8 years, with the next one not expected to occur until around 2068. While some members of the team don’t expect to be around to study that event, they hope that the work they leave in cultivating these long-term sky surveys gives future scientists a foundation to make all sorts of new, exciting discoveries.
“We want our data to be accessible a hundred years from now, even if we are not around,” said Stanek. “The main point of ASAS-SN is, if something happens in the sky, we’ll have historical data for it.”
In the meantime, the team wants to make use of larger telescopes like The James Webb Space Telescope and the ground-based Large Binocular Telescope Observatory to make more complete observations of the system as it returns to full brightness.
“This study is a particularly interesting example of a broader class of still very strange objects,” said Stanek. “We learn more about astrophysics when we find things that are unusual, because it pushes our theories to the test.”
Other Ohio State co-authors include Brayden JoHantgen, Michael Tucker, Lucy Lu and Dominick Rowan, as well as scientists at Boston University, University of Hawai’i, Carnegie Observatories, University of Vienna, Florida State University, The University of Melbourne, University of California, Santa Cruz and Ball State University.
This work was supported by the National Science Foundation and NASA, the Gordon and Betty Moore Foundation and the Alfred P. Sloan Foundation.
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Contact: Raquel Forés-Toribio, Forestoribio.1@osu.edu
Written by: Tatyana Woodall, Woodall.52@osu.edu
Journal
The Open Journal of Astrophysics
Article Title
ASASSN-24fw: An 8-month long, 4.1 mag, optically achromatic and polarized dimming event
Article Publication Date
7-Aug-2025
