SwRI scientists studied the composition of a small shard of a meteoroid to determine that it likely originated from a previously unknown overhead asteroid. This false-color photomicrograph of the meteoroid sample shows the unexpected amphibole crystals identified in orange. Credit: NASA / USRA / Lunar and Planetary Institute
Mineralogy indicates large, water-rich parent asteroid for carbonaceous chondrite meteorite.
A team of scientists led by the Southwest Research Institute has identified a possible new parent asteroid of a meteorite by studying a tiny shard of a meteorite that arrived on Earth a decade ago. The composition of a piece of the meteorite Almahata Sitta (AhS) indicates that the mother body was an asteroid about the size of Ceres, the largest object in the main asteroid belt, and formed in the presence of water at intermediate temperatures and press.
“Carboniferous chondrite (CC) meteorites record geological activity during the earliest stages of the solar system and provide insight into the history of their parent bodies,” said SwRI Staff Scientist Dr. Vicky Hamilton, lead author of a paper published in Nature Astronomy outlining this. Research. “Some of these meteorites are dominated by minerals that provide evidence of exposure to water at low temperatures and pressures. The composition of other meteorites indicates heating in the absence of water. Evidence for metamorphosis in the presence of water under intermediate conditions is virtually absent so far. “
Asteroids – and the meteors and meteorites that sometimes come out – are remnants of the formation of our solar system 4.6 billion years ago. Most are in the main asteroid belt between the orbits of Mars and Jupiterbut collisions and other events have broken them up, throwing debris into the inner solar system. In 2008, a 9-ton, 4-meter asteroid entered Earth’s atmosphere and exploded in about 600 meteorites over Sudan. This was the first time scientists had predicted an asteroid impact before entering, allowing for the recovery of 23 pounds of samples.
“We were assigned a 50 milligram AhS sample to study,” said Hamilton. “We mounted and polished the small shard and used an infrared microscope to examine its composition. Spectral analysis identified a range of hydrated minerals, particularly amphibole, indicating intermediate temperatures and pressures and a prolonged period of aqueous change on a parent planoid at least 400 and up to 1100 miles in diameter. “
Amphiboles are rare in CC meteorites as they have only been previously identified as a trace component in the Allende meteorite. “AhS is an accidental source of information about early solar system materials that are not represented by CC meteorites in our collections,” said Hamilton.
Orbital spectroscopy of asteroids Ryugu and Bennu visited by the Japanese Hayabusa2 and NASA‘s OSIRIS-REx spacecraft match aqueously altered CC meteorites this year, suggesting that both asteroids differ from most known meteorites in terms of their hydration states and evidence for large-scale, low-temperature hydrothermal processes. These missions collected samples from the surfaces of the asteroids for return to Earth.
“If the compositions of the Hayabusa2 and OSIRIS-REx samples are different from what we have in our meteorite collections, it could mean that their physical properties are not causing the processes of ejection, transit and penetration through Earth’s atmosphere. survive. in their original geological context, ”says Hamilton, who is also part of the OSIRIS-REx science team. “However, we think there are more carbonaceous chondrite materials in the solar system than represented by our collections of meteorites.”
Reference: “Meteoritic Evidence for a Ceres-Sized Hydrous Carboniferous Chondrite Parent Asteroid” by VE Hamilton, CA Goodrich, AH Treiman, HC Connolly Jr, ME Zolensky and MH Shaddad, December 21, 2020, Nature astronomy.
DOI: 10.1038 / s41550-020-01274-z