Arrokoth’s Necklace. (arXiv:1902.00997v3 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Katz_J/0/1/0/all/0/1">J. I. Katz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_S/0/1/0/all/0/1">S. Wang</a>
Flyby images of (486958) Arrokoth (Ultima Thule, 2014 MU$_{69}$) show a
comparatively bright “necklace” in the neck, or cleft between its two lobes, in
contrast to its generally low albedo. We suggest that the necklace may be the
result of thermally controlled ice deposition. The necklace is found in the
most (orbitally averaged) shaded part of its surface. It may consist of clean,
high albedo, ice condensed from vapor sublimed by dirty, low albedo, ice
elsewhere; clean ice accumulates where the maximum temperatures are the lowest.
Ammonia and propane have the necessary mesovolatile vapor pressure. Surrounding
gas in the proto-Solar System would facilitate redeposition of molecules
sublimed by warmer parts of the surface into the cleft, as well as smoothing
the surface and explaining, by hydrodynamic drag, Arrokoth’s slow (compared to
its breakup rate) rotation. Alternatively, a layer of hoarfrost thick enough
($gtrsim 0.1,mu$) to have a high albedo could have formed more recently.
Flyby images of (486958) Arrokoth (Ultima Thule, 2014 MU$_{69}$) show a
comparatively bright “necklace” in the neck, or cleft between its two lobes, in
contrast to its generally low albedo. We suggest that the necklace may be the
result of thermally controlled ice deposition. The necklace is found in the
most (orbitally averaged) shaded part of its surface. It may consist of clean,
high albedo, ice condensed from vapor sublimed by dirty, low albedo, ice
elsewhere; clean ice accumulates where the maximum temperatures are the lowest.
Ammonia and propane have the necessary mesovolatile vapor pressure. Surrounding
gas in the proto-Solar System would facilitate redeposition of molecules
sublimed by warmer parts of the surface into the cleft, as well as smoothing
the surface and explaining, by hydrodynamic drag, Arrokoth’s slow (compared to
its breakup rate) rotation. Alternatively, a layer of hoarfrost thick enough
($gtrsim 0.1,mu$) to have a high albedo could have formed more recently.
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