March 18, 2025, Mountain View, CA -- Where do meteorites of different type come from? In a review paper in the journal Meteoritics & Planetary Science, published online this week, astronomers trace the impact orbit of observed meteorite falls to several previously unidentified source regions in the asteroid belt.
"This has been a decade-long detective story, with each recorded meteorite fall providing a new clue," said meteor astronomer and lead author Peter Jenniskens of the SETI Institute and NASA Ames Research Center. "We now have the first outlines of a geologic map of the asteroid belt."
Ten years ago, Jenniskens teamed up with astronomer Hadrien Devillepoix of Curtin University and colleagues in Australia to build a network of all-sky cameras in California and Nevada that can capture and track the bright light of meteorites as they hit the Earth's atmosphere. Many institutes and citizen scientists participated in this effort over the years.
"Others built similar networks spread around the globe, which together form the Global Fireball Observatory," said Devillepoix. "Over the years, we have tracked the path of 17 recovered meteorite falls."
Many more fireballs were tracked by doorbell and dashcam video cameras from citizen scientists around the globe and by other dedicated networks.
"Altogether, this quest has yielded 75 laboratory-classified meteorites with an impact orbit tracked by video and photographic cameras," said Jenniskens. "That proves to be enough to start seeing some patterns in the direction from which the meteorites approach Earth."
Most meteorites originate from the asteroid belt, a region between Mars and Jupiter where over a million asteroids larger than 1 kilometer circle the Sun. Those rocks originate from a small number of larger asteroids that broke in collisions, the debris fields of which litter the region. Even today, asteroids collide to create debris fields within these asteroid families, called clusters.
"We now see that 12 of the iron-rich ordinary chondrite meteorites (H chondrites) originated from a debris field called "Koronis," which is located low in the pristine main belt," said Jenniskens. "These meteorites arrived from low-inclined orbits with orbital periods consistent with this debris field."
Astronomers can measure how long ago these rocks were dug up from below the asteroid's surface by measuring the level of radioactive elements created by exposure to cosmic rays. This cosmic-ray exposure age of the meteorites proves to match the dynamical age of some of the asteroid debris fields. Scientists determine the dynamical age of debris fields by measuring how much asteroids of different size have spread over time.
"By measuring the cosmic ray exposure age of meteorites, we can determine that three of these twelve meteorites originated from the Karin cluster in Koronis, which has a dynamical age of 5.8 million years, and two came from the Koronis2 cluster, with a dynamical age of 10-15 million years," said Jenniskens. "One other meteorite may well measure the age of the Koronis3 cluster: about 83 million years."
Jenniskens and Devillepoix also found a group of H-chondrites on steep orbits that appear to originate from the Nele asteroid family in the central main belt, which has a dynamical age of about 6 million years. The nearby 3:1 mean-motion resonance with Jupiter can pump up the inclinations to those observed. A third group of H chondrites that have an exposure age of about 35 million years originated from the inner main belt.
"In our opinion, these H chondrites originated from the Massalia asteroid family low in the inner main belt because that family has a cluster of about that same dynamical age," said Jenniskens. "The asteroid that created that cluster, asteroid (20) Massalia, is an H chondrite type parent body."
Jenniskens and Devillepoix find that low iron (L chondrite) and very low iron (LL chondrite) meteorites come to us primarily from the inner main belt. Scientists have long linked the LL chondrites to the Flora asteroid family on the inner side of the asteroid belt, and they have confirmed that connection.
"We propose that the L chondrites originated from the Hertha asteroid family, located just above the Massalia family," said Jenniskens. "Asteroid Hertha doesn't look anything like its debris. Hertha is covered by dark rocks that were shock-blackened, indicative of an unusually violent collision. The L chondrites experienced a very violent origin 468 million years ago when these meteorites showered Earth in such numbers that they can be found in the geologic record."
Knowing from what debris field in the asteroid belt our meteorites originate is important for planetary defense efforts against Near Earth Asteroids. An approaching asteroid's orbit can provide clues to its origin in the asteroid belt in the same way as meteorite orbits.
"Near Earth Asteroids do not arrive on the same orbits as meteorites, because it takes longer for these to evolve to Earth." said Jenniskens. "But they do come from some of the same asteroid families."
Jenniskens and Devillepoix discuss the links of several other meteorite types to their source regions. Not all assignments are certain.
"We are proud about how far we have come, but there is a long way to go," said Jenniskens, "Like the first cartographers who traced the outline of Australia, our map reveals a continent of discoveries still ahead when more meteorite falls are recorded."
What's coming next? Asteroids directly meet meteorites when observed in space before impacting Earth and then recovered. Jenniskens guided the recovery of the first such small asteroid in 2008, called asteroid 2008 TC3, and we are about to see a lot more thanks to new astronomical facilities coming online.
Link to the paper:
https://onlinelibrary.wiley.com/doi/full/10.1111/maps.14321
About the SETI Institute
Founded in 1984, the SETI Institute is a non-profit, multi-disciplinary research and education organization whose mission is to lead humanity's quest to understand the origins and prevalence of life and intelligence in the universe and share that knowledge with the world. Our research encompasses the physical and biological sciences and leverages data analytics, machine learning, and advanced signal detection technologies. The SETI Institute is a distinguished research partner for industry, academia, and government agencies, including NASA and the National Science Foundation.
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