[Baps] PLS 3/5 - Brynna Downey - Evolution of the Moon's orbital inclination

[John B. Biersteker]

Hello all,

We’re excited to announce that this week’s planetary seminar will feature Brynna Downey from UCSC. She will be joining us remotely to discuss the orbital evolution of our Moon and what it can tell us about the Moon’s origin and evolution. Please join us on Tuesday March 5 at 12:30 PM in 54-517 or on Zoom. Lunch will be provided and we encourage you to arrive a bit early to get food.

Brynna is available in the afternoon for one-on-one chats. You can sign up for a meeting here<https://docs.google.com/spreadsheets/d/1wuyAQJDDi_B8jsNMKORdo6ksY0iosEYF1qp_VU_znNY/edit?usp=sharing>.

Talk details and Zoom information are below. We hope to see you there!

-John

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Evolution of the Moon's orbital inclination

Abstract: The Moon’s orbit is currently inclined despite having formed on a zero-inclination orbit after the Moon-forming giant impact. Various theories have been proposed to explain why the Moon’s orbit is inclined. We test the viability of these theories by reconstructing the thermal–orbital history of the Moon. In particular, we include tides in the lunar magma ocean, which increases inclination damping, and the effect of a fossil figure, which records the Moon’s orbital state at an earlier point in time. We find that an early inclination is preserved only if the solid-body of the early Moon were less dissipative than at present. If instabilities at the Laplace plane transition were the source of the inclination, then the Moon had to recede slowly, which is consistent with previous findings of a weakly dissipative early Earth. If collisionless encounters with planetesimals up to 140 Myr after Moon formation excited the inclination, then the Moon had to migrate quickly to pass through the Cassini state transition at 33 Earth radii and reach a period of limited inclination damping. The fossil figure was likely established before 16 Earth radii to match the present-day degree-2 gravity field observations.

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Zoom link: https://mit.zoom.us/j/93069069393
PW: 54100
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