From Eos : “A Deep-Space Origin for Volatile-Rich Asteroids”

From AGU
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From Eos

19 January 2022
Francis Nimmo

Spectral data and modeling suggest that volatile-rich main-belt asteroids initially formed at much greater distances from the Sun (>10 AU).

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Processes envisaged to have taken place. The body accretes (1) and then heats up and differentiates (2) into a rock rich-interior and an icier exterior. The body then refreezes (3) with the inner and outer regions having different mineralogies and spectral absorptions. On impact disruption (4) fragments from the core will preferentially survive to become meteorites. Credit: Kurokawa et al., 2021, (Figure 7).

The origin of the Earth’s volatiles (e.g., water) is a perennial puzzle.

Most likely they come primarily from volatile-rich (“carbonaceous”) meteorites, which are spectrally similar to volatile-rich asteroids in the main belt.

But as Kurokawa et al. [2021] [AGU Advances] show, the similarity is not exact: some of the main belt asteroids contain ammoniated clays which are not seen in the meteorites.

This is important because ammonia is not expected to be stable so close to the Sun.

Instead, Kurokawa et al. propose that the volatile-rich asteroids formed at greater distances (>10 AU) and were then scattered inwards to the main belt.

The absence of ammoniated clays in meteorites is explained by positing a layered structure, with the more indurated, ammonia-free rocky core expected to survive impact disruption and atmospheric re-entry.

This study bolsters other recent isotopic arguments that an outer solar system reservoir contributed significantly to the Earth’s growth.

See the full article here .

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