Thermophysical, Gravitational, and Geomorphology Properties of 2014 MU69
Abstract
NASA's New Horizons spacecraft imaging of 2014 MU69 on January 1, 2019 revealed a ~16-hr rotating bi-lobed object whose constituents, informally referred to as Ultima and Thule (or collectively "UT"), appear nearly spherical with ~9.5 km and ~7.1 km radii (respectively). Ultima and Thule have similar colors with measured albedos ~ 0.06, indicating that UT is a typical member of the Cold Classical Kuiper Belt class of objects. Detailed image analysis and shape modeling (also presented at this meeting) suggests that UT's obliquity is nearly 99o and Ultima is relatively flattened by comparison to Thule. The surface morphology admits features ranging from small pits, large craters, smooth undifferentiated planes interspersed with scarps possibly derived from sublimation-driven landform evolutionary processes (also discussed at this meeting). Of particular note is the presence of relatively bright materials observed in UT's neck region. Additionally, the onboard radiometer ("REX") observed UT on its backlit side and its beam (4cm wavelength, X-band), containing the entirety of UT's sky projection, measured an approximate brightness temperature of about TB = 29K ± 5K. However the depth to which the radar beam penetrated UT's near subsurface was not independently measured and therefore requires theoretical modeling. In this talk we survey the gravitational and thermophysical properties of UT derived from detailed global theoretical modeling of the body based on the most recent shape model developed by Beyer and Porter. We place these results into the context of UT's observed features. We calculate the body's geopotential surfaces and local slopes, and based on previous theoretical considerations we conjecture about UT's average density. Further analysis reveals that both of UT's lobes are remarkably well-aligned with their principal axes being nearly parallel. Due to self-shadowing we find that the neck region is on average cooler than the rest of the body despite significant surface re-radiation into the zone. Thule's large deep crater, informally named Maryland, is about 1K warmer than the surrounding regions. We predict that the surface temperature of the unlit side to be about 16K suggesting that the REX beam may have penetrated anywhere from 5-50 cm beneath the surface. We consider these properties in light of UT's possible evolutionary scenarios.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23541905U