Meteor evidence found for a previously unknown asteroid

SwRI scientists studied the composition of a small meteoroid shard to determine that it probably originated from a previously unknown parent asteroid. This fake color photomicrograph of a meteoroid sample shows unexpected amphibole crystals identified by an orange color. Credit: NASA / USRA / Lunar and Planetary Institute

Mineralogy indicates a large, water-rich parent asteroid of the carbon chondrite meteorite.

A team of scientists led by the Southwest Research Institute has identified a potentially new meteorite parent asteroid by studying a small meteorite shard that arrived on Earth about ten years ago. The composition of the Almahata Sitta (AhS) meteorite piece indicates that its parent body was an asteroid about the size of Ceres, the largest object in the main belt of the asteroid, and formed in the presence of water at medium temperatures and pressures.

“Carbon 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, the first author of a paper published in the journal Nature Astronomy, in which this highlighted 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 suggests warming in the absence of water. Evidence of metamorphism in the presence of water in medium conditions is so far absent. “

Asteroids – both meteors and meteorites that sometimes come from them – are remnants of the formation of our solar system 4.6 billion years ago. Most of them live in the main belt of asteroids between orbits March i Jupiter, but collisions and other events broke them and threw the remains into the inner solar system. In 2008, an asteroid with a diameter of 9 tons and a diameter of 13 feet entered the Earth’s atmosphere, exploding in about 600 meteorites above Sudan. This is the first time that scientists predicted an asteroid impact before entering and enabled the recovery of 23 kilograms of samples.

“We were assigned a 50 milligram AhS sample for the study,” Hamilton said. “We mounted and polished a small shard and examined its composition with an infrared microscope. Spectral analysis identified a number of hydrated minerals, particularly amphibole, indicating mean temperatures and pressures and an extended period of water changes on the parent asteroid at least 400 and up to 1,100 miles in diameter. “

Amphipholes are rare in CC meteorites because they were only previously identified as a trace component in the Allende mendeorite. “AhS is a considerable source of information about early materials of the solar system that are not represented by CC meteorites in our collections,” Hamilton said.

Orbital spectroscopy of the asteroids Ryugu and Bennu was visited by the Japanese Hayabusa2 and NASA‘s OSIRIS-REx This year’s spacecraft is in line with water-modified CC meteorites and suggests that both asteroids differ from the most well-known meteorites in terms of their hydration state and evidence for large low-temperature hydrothermal processes. These missions collected samples from asteroid surfaces to return to Earth.

“If the compositions of the Hayabusa2 and OSIRIS-REx samples differ from what we have in our meteorite collections, it could mean that their physical properties cause them not to survive the process of ejection, transit and entry through the Earth’s atmosphere, at least in their original geological context.” said Hamilton, who is also a member of the OSIRIS-REx scientific team. “However, we think there are more carbon chondritic materials in the solar system than our meteorite collections represent.”

Reference: “Meteorite evidence of water rich in hydrocarbon chondrite parent asteroid the size of Ceres” by VE Hamilton, CA Goodrich, AH Treiman, HC Connolly Jr, ME Zolensky and MH Shaddad, December 21, 2020, Astronomy of nature.
DOI: 10.1038 / s41550-020-01274-z

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