Miki Nakajima, University of Rochester

University of Arizona, Theoretical Astrophysics Program (TAP) Colloquia Series
TITLE:
Origin of Moons in the Solar System and Beyond
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 on a very short timescale. This problem could be avoided if large moonlets ( greater than 1000 km) form very quickly by the process called streaming instability. We investigate this possibility by conducting numerical simulations. We will discuss the implications of this study for moons in the solar system and extrasolar systems (exomoons). We will also briefly describe our ongoing work on terrestrial craters (Vredefort and Sudbury impact basins) as well as shock experiments at the Laboratory of Laser Energetics at the University of Rochester.
BIO:
Miki comes to us from the University of Rochester where she is currently an Assistant Professor, Earth and Environmental Sciences with a secondary appointment in Physics and Astronomy and Laboratory for Laser Energetics. She was a Postdoctoral Fellow at the Carnegie Institution for Science and received her Ph.D. and M.Sc. in Planetary Science from the California Institute of Technology, an M.Sc. in Earth and Planetary Sciences from the Tokyo Institute of Technology, and participated in an Exchange Program in Astronomy and Astrophysics at the University of California, Santa Cruz.