Haumea: Internal Structure and Collisional Family

National Aeronautics and Space Administration Solar System Workings Program

Subaward to PSI from Arizona State University

PI: Steven Desch (Arizona State University)

Start Date: 10/12/2018
Project #: 1627
End Date: 10/11/2022
Award #: ASUB00000230
Project Description

Haumea is a dwarf planet in the Kuiper Belt that is a rapid rotator (P=3.9 hr) with a pronounced light curve, despite an apparently uniform surface, implying a triaxial ellipsoid shape consistent with a Jacobi ellipsoid. Haumea possesses two moons and a ring, and is the only Kuiper Belt Object with a known collisional family, of about a dozen icy fragments . It is inferred to have suffered a large collision in the past that stripped its icy mantle. Haumea therefore offers a unique opportunity to probe the interior of an icy body, and to investigate the properties of mantle-stripping collisions. These are processes ongoing throughout the solar system.

The first goal is to constrain the size and shape of Haumea, and the size and shape of its rocky core. Until this year it was thought that Haumea had a large rocky core and thin ice mantle, but new observations of Haumea's shadow during an occultation event by Ortiz et al. (2017) indicate a large icy mantle, and possibly a shape not consistent with a fluid in hydrostatic equilibrium.

It is important to constrain the origins of the Haumea collisional family, to learn about mantle-stripping events generally. There are various theories about its origin, including the Leinhardt et al. (2010) "graze-and-merge" scenario, and the Schlichting & Sari (2009) moon disruption scenario. The Leinhardt et al. (2010) scenario is consistent with the angular momentum of Haumea, but not as obviously with the low mass of ejected ice and the low delta v of the collisional family members. The Schlichting & Sari (2009) scenario is consistent with the low delta v, but requires tidal migration of an impact- formed moon, and is less probable.

We propose a campaign of theoretical research designed to test hypotheses of Haumea's origin.

* We will use a new code written by the Desch group, to calculate the figure of equilibrium of a differentiated, rapidly rotating non-axisymmetric fluid bodies. We will use this in conjunction with extensive, existing (published or in-hand) observational data from photometric light curves, satellite astrometry, Haumea-Namaka mutual events, and now the occultation data, to constrain the size and internal structure of Haumea today. We will constrain how much rocky material is mixed in with an icy mantle, and estimate albedos.

* We will use the geochemistry code IcyDwarf written by the Desch research group, to constrain the internal thermal evolution and differentiation of the proto-Haumea and the post-collision Haumea. We will especially consider the possibility of undifferentiated rock/ice crusts in the pre-collision bodies, and the extent of hydrothermal circulation and water-rock interactions in the core of the proto-Haumea and post-impact Haumea.

* We will better constrain the dynamics of the collision in the graze-and-merge scenario, testing whether there is a correlation between delta v and the depth of the material on the proto-Haumea. For various depths of undifferentiated rock/ice crust we will calculate the delta v of both icy and rock/ice ejected material.* We will better characterize the collisional family. We will expand the list of candidate family members and derive the proper orbital elements and delta v for each. We will use color data to look for correlations between delta v and color.

Our modeling and observational analysis will provide the most comprehensive investigation of Haumea's internal structure, and of the circumstances that generated Haumea and its collisional family. We will assess the extent of water-rock interaction on small icy worlds, with implications for astrobiology. We will probe the dynamcis of mantle-stripping, drawing insights to enhance the science return from the upcoming Psyche mission.

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