TY - JOUR
T1 - Thermal stability of ice on Ceres with rough topography
AU - Hayne, P. O.
AU - Aharonson, Oded
N1 - We thank Norbert Schorghofer, Bruce Bills, and Nicolas Rambaux for valuable discussions. Mikhail Kreslavsky and Matthew Siegler provided exceptionally thoughtful reviews, from which the paper benefited immensely. A workshop hosted by Thomas McCord and Julie Castillo‐Rogez at the Bear Fight Institute provided the initial inspiration for this study, which was fueled by continued workshops and support from the Weizmann Institute of Science (WIS). Oded Aharonson wishes to acknowledge important support from the Helen Kimmel Center for Planetary Science, the WIS Minerva Center, and ISF I‐CORE program. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Copyright 2015, all rights reserved. The source code and input files for the models used in this study are available from the authors upon request ([email protected]), pending approval for public release by NASA/JPL.
PY - 2015/9/1
Y1 - 2015/9/1
N2 - The dwarf planet Ceres may have an ice‐rich crust, and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation. We model surface and subsurface temperatures on Ceres to assess lifetimes of water ice and other volatiles. Topographic shadowing allows a small but nonnegligible fraction (∼0.4%) of Ceres' surface to be perennially below the ∼110 K criterion for 1 Gyr of stability. These areas are found above 60° latitude. Other molecules (CH3OH, NH3, SO2, and CO2) may be cold trapped in smaller abundances. A model for the transport, gravitational escape, and photoionization of H2O molecules suggests net accumulation in the cold traps. Buried ice is stable within a meter for > 1 Gyr at latitudes higher than ∼50°. An illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo (>0.5) at present obliquity. If the obliquity exceeded 5° in the geologically recent past, then a putative polar cap would have been erased. At latitudes 0°–30°, ice is stable under solar illumination only briefly (∼10–100 years), unless it has high albedo and thermal inertia, in which case lifetimes of > 104 years are possible. Finally, a small hemispheric asymmetry exists due to the timing of Ceres' perihelion passage, which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate. Our model results are potentially testable during the Dawn science mission.
AB - The dwarf planet Ceres may have an ice‐rich crust, and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation. We model surface and subsurface temperatures on Ceres to assess lifetimes of water ice and other volatiles. Topographic shadowing allows a small but nonnegligible fraction (∼0.4%) of Ceres' surface to be perennially below the ∼110 K criterion for 1 Gyr of stability. These areas are found above 60° latitude. Other molecules (CH3OH, NH3, SO2, and CO2) may be cold trapped in smaller abundances. A model for the transport, gravitational escape, and photoionization of H2O molecules suggests net accumulation in the cold traps. Buried ice is stable within a meter for > 1 Gyr at latitudes higher than ∼50°. An illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo (>0.5) at present obliquity. If the obliquity exceeded 5° in the geologically recent past, then a putative polar cap would have been erased. At latitudes 0°–30°, ice is stable under solar illumination only briefly (∼10–100 years), unless it has high albedo and thermal inertia, in which case lifetimes of > 104 years are possible. Finally, a small hemispheric asymmetry exists due to the timing of Ceres' perihelion passage, which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate. Our model results are potentially testable during the Dawn science mission.
UR - http://www.scopus.com/inward/record.url?scp=84945186704&partnerID=8YFLogxK
U2 - https://doi.org/10.1002/2015JE004887
DO - https://doi.org/10.1002/2015JE004887
M3 - مقالة
SN - 2169-9097
VL - 120
SP - 1567
EP - 1584
JO - Journal of Geophysical Research-Planets
JF - Journal of Geophysical Research-Planets
IS - 9
ER -