Hydrothermal activities on C-complex asteroids induced by radioactivity

TL;DR

This paper presents evidence that internal radioactive decay caused hydrothermal activity and dehydration in C-complex asteroids, explaining their spectral properties and thermal metamorphism without impact heating.

Contribution

It provides the first radiometric age for Ca-carbonates in a meteorite, linking internal radioactivity to asteroid thermal evolution and dehydration processes.

Findings

Old age of 4564.7 million years for Ca-carbonates indicating early aqueous alteration.

Presence of high-temperature Ca-sulfates suggests thermal metamorphism at >300°C.

Dehydrated C-complex asteroids likely result from internal heating by radioactivity.

Abstract

C-complex asteroids, rich in carbonaceous materials, are potential sources of Earth's volatile inventories. They are spectrally dark resembling primitive carbonaceous meteorites, and thus, C-complex asteroids are thought to be potential parent bodies of carbonaceous meteorites. However, the substantial number of C-complex asteroids exhibits surface spectra with weaker hydroxyl absorption than water-rich carbonaceous meteorites. Rather, they best correspond to meteorites showing evidence for dehydration, commonly attributed to impact heating. Here, we report an old radiometric age of 4564.7 million years ago for Ca-carbonates from the Jbilet Winselwan meteorite analogous to dehydrated C-complex asteroids. The carbonates are enclosed by a high-temperature polymorph of Ca-sulfates, suggesting thermal metamorphism at >300{\deg}C subsequently after aqueous alteration. This old age indicates the early onset of aqueous alteration and subsequent thermal metamorphism driven by the decay of short-lived radionuclides rather than impact heating. The breakup of original asteroids internally heated by radioactivity should result in asteroid families predominantly consisting of thermally metamorphosed materials. This explains the common occurrence of dehydrated C-complex asteroids.