"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."
In pursuit of this goal, Jenniskens collaborated with Hadrien Devillepoix of Curtin University and other researchers to deploy a network of all-sky cameras across California and Nevada. These instruments captured the brilliant descent of meteorites entering Earth's atmosphere. Their global counterparts, including numerous dedicated networks and contributions from citizen scientists using doorbell and dashcam footage, expanded the observational reach worldwide.
"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."
From this international effort, 75 meteorites have been analyzed in laboratories, with their atmospheric entry paths accurately determined through video and photographic evidence. This data enabled astronomers to identify trends in the directions from which these space rocks arrive.
The majority of these meteorites can be traced back to the asteroid belt, a region between Mars and Jupiter populated by more than a million asteroids over 1 kilometer in size. Many of these originated from larger parent asteroids fragmented by collisions, resulting in debris fields known as clusters. Collisions still occur today, perpetuating the cycle of debris creation.
"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."
To establish the timeline of these fragments' journeys, researchers measured the cosmic ray exposure age of the meteorites, reflecting how long they had been exposed to space radiation since being dislodged from their parent bodies. These findings align with the known dynamical ages of their respective asteroid clusters.
"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."
The study also identified a group of H chondrites with steep orbital paths linked to the Nele asteroid family in the central main belt, whose dynamical age is around 6 million years. The gravitational influence of Jupiter, particularly the 3:1 mean-motion resonance, helps elevate the orbits to those observed. Another group of H chondrites, with an exposure age of roughly 35 million years, is believed to originate 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."
Further analysis revealed that meteorites with lower iron content, including L chondrites and LL chondrites, predominantly derive from the inner main belt. LL chondrites have long been associated with the Flora asteroid family, a connection that has now been reaffirmed.
"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."
Understanding the asteroid belt origins of meteorites offers valuable insight into planetary defense. Determining an approaching asteroid's orbit can suggest its source in the asteroid belt, aiding impact risk assessments.
"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 explored links between additional meteorite types and their sources, though some associations remain tentative.
"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."
Future advances will come from observations of asteroids in space just before impact, followed by ground recovery. Jenniskens directed the recovery of asteroid 2008 TC3, the first such observed event, and anticipates many more with upcoming astronomical technologies.
Research Report:Review of asteroid, meteor, and meteorite-type links
Related Links
SETI Institute
Asteroid and Comet Mission News, Science and Technology
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