Astrophysical and Planetary Sciences Colloquium

Monday, February 08, 2021 at 12:40

https://cuboulder.zoom.us/j/96981439846

Miki Nakajima, University of Rochester

"Origin of Earth, the Moon, and exomoons"

A Pretty Image from the Talk

Abstract:

The Apollo lunar samples reveal that Earth and the Moon have strikingly similar isotopic ratios, suggesting that these bodies may share the same source materials. This leads to the "standard" giant impact hypothesis, suggesting the Moon formed from a disk that was generated by an impact between Earth and a Mars-sized object. This disk would have had high temperature (~ 4000 K), and its silicate vapor mass fraction would have been ~20 wt %. However, impact simulations indicate that this model does not mix the two bodies well, making it challenging to explain the similarity. In contrast, recent studies suggest that more energetic impact models that produce higher vapor mass fractions (~80-90 wt%) could mix the two bodies, naturally solving the problem. However, these energetic models may have a challenge during the Moon accretion phase. Our analyses suggest that km- sized moonlets experience a strong gas drag from the vapor portion of the disk and fall onto Earth in a very short timescale. This problem could be avoided if large moonlets (>1000 km) form very quickly by the process called streaming instability. We investigate this possibility by conducting numerical simulations with the code called Athena. We will also discuss implications of this study for moons in extrasolar systems (exomoons).

 

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