Thermal Evolution of Hydrated Asteroids Inferred from Oxygen Isotopes

TY - JOUR

T1 - Thermal Evolution of Hydrated Asteroids Inferred from Oxygen Isotopes

AU - Vacher, Lionel G.

AU - Piralla, Maxime

AU - Gounelle, Matthieu

AU - Bizzarro, Martin

AU - Marrocchi, Yves

PY - 2019/9/10

Y1 - 2019/9/10

N2 - Chondrites are fragments of unmelted asteroids that formed due to gravitational instabilities in turbulent regions of the Solar protoplanetary disk. Hydrated chondrites are common among meteorites, indicating that a substantial fraction of the rocky bodies that formed early in the solar system accreted water ice grains that subsequently melted due to heat released by the radioactive decay of 26Al. However, the thermal histories of asteroids are still largely unknown; increased knowledge would provide fundamental information on their timing of accretion and their physical characteristics. Here we show that hydrated meteorites (CM chondrites) contain previously uncharacterized calcium carbonates with peculiar oxygen isotopic compositions (Δ17O ≈ -2.5‰), which artificially produce the mass-independent trend previously reported for carbonates. Based on these isotopic data, we propose a new model to quantitatively estimate the precipitation temperatures of secondary phases (carbonates and serpentine). It reveals that chondritic secondary phases recorded a gradual increase in temperature during the extent of aqueous alteration, from -10°C to a maximum of 250°C. We also show that the thermal path of C-type asteroids is independent of the initial oxygen isotopic composition of the primordial water ice grains that they accreted. Our estimated temperatures for hydrated asteroids remain lower than those experienced by other carbonaceous chondrites, providing strong constraints for modeling the formation conditions and size distribution of water-rich asteroids, especially in anticipation of the return of samples of water-rich asteroids to Earth by the OSIRIS-REx and Hayabusa2 missions.

AB - Chondrites are fragments of unmelted asteroids that formed due to gravitational instabilities in turbulent regions of the Solar protoplanetary disk. Hydrated chondrites are common among meteorites, indicating that a substantial fraction of the rocky bodies that formed early in the solar system accreted water ice grains that subsequently melted due to heat released by the radioactive decay of 26Al. However, the thermal histories of asteroids are still largely unknown; increased knowledge would provide fundamental information on their timing of accretion and their physical characteristics. Here we show that hydrated meteorites (CM chondrites) contain previously uncharacterized calcium carbonates with peculiar oxygen isotopic compositions (Δ17O ≈ -2.5‰), which artificially produce the mass-independent trend previously reported for carbonates. Based on these isotopic data, we propose a new model to quantitatively estimate the precipitation temperatures of secondary phases (carbonates and serpentine). It reveals that chondritic secondary phases recorded a gradual increase in temperature during the extent of aqueous alteration, from -10°C to a maximum of 250°C. We also show that the thermal path of C-type asteroids is independent of the initial oxygen isotopic composition of the primordial water ice grains that they accreted. Our estimated temperatures for hydrated asteroids remain lower than those experienced by other carbonaceous chondrites, providing strong constraints for modeling the formation conditions and size distribution of water-rich asteroids, especially in anticipation of the return of samples of water-rich asteroids to Earth by the OSIRIS-REx and Hayabusa2 missions.

KW - meteorites, meteors, meteoroids

KW - minor planets, asteroids: general

KW - protoplanetary disks

U2 - 10.3847/2041-8213/ab3bd0

DO - 10.3847/2041-8213/ab3bd0

M3 - Journal article

SN - 2041-8205

VL - 882

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

IS - 2

ER -