NOVAC General Meeting – Sunday March 11, at 7:00 PM at GMU

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Come join NOVAC members to hear Dr. Miki Nakajima from the University of Rochester speak about the origin of the Earth and Moon. Dr. Nakijima earned her PhD in Planetary Science with a minor in Computational Science and Engineering from the California Institute of Technology. Guests are welcome at our meetings.

Topic: Origin of the Earth and Moon

The Moon likely formed by a collision between Earth and an impactor. This impact formed a hot and partially vaporized disk around Earth from which our Moon accreted. The details of the impact, such as the impactor size and velocity, have been actively debated. Here, we suggest that the impact can be constrained by the state of the Earth’s mantle; short-lived isotopes of the Earth’s mantle suggest that the Earth’s mantle has never been mixed even by the Moon forming impact. Another potential clue arises from the Earth’s core. According to recent geophysical and dynamical studies, the Earth’s core may have developed a compositionally stratified structure during its formation, which would have suppressed an early dynamo of the Earth. However, this appears to be inconsistent with paleomagnetic measurements that indicate the presence of an early dynamo. One of the potential solutions to these problems is that the Moon-forming impact mixed the core and reset the stratification without completely mixing the mantle. To understand the initial states of the Earth’s mantle and core, we simulate impact processes using a scheme called smoothed particle hydrodynamics (SPH). Our simulations show that the mantle heterogeneity could have survived the giant impact while the core could have dynamically mixed if the impactor was about the size of Mars and the impact velocity was similar to the escape velocity. More energetic impact models are not favorable because they would have mixed the mantle. We also show that water loss from the disk by hydrodynamic escape was minor, which can explain some of the studies that suggest that the Moon may be as wet as Earth. Finally, we will briefly discuss volatile loss by hydrodynamic escape from the Martian moons, Phobos and Deimos. We suggest that their water abundances, which can be tested by the future sample mission (Martian Moons Exploration, MMX), could constrain the origin of the moons.

• Important to know
Meetings start at 7:00 PM. If you come earlier you can do a little socializing. Paid parking near the meeting room is available in the Shenandoah parking structure.

Meeting attendees are invited to join our informal pre-meeting dinner at Red Hot and Blue, 4150 Chain Bridge Rd, Fairfax, VA 22030 at 5:30 p.m. The pre-meeting dinner is an excellent way to meet club members, welcome newcomers, and renew old friendships.

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