A Sublimation-driven Exospheric Model of Ceres

Tu, L.; Ip, Wing-Huen; Wang, Y.-C.

doi:10.1016/j.pss.2014.09.002

Cited by 16 publications

(16 citation statements)

References 38 publications

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“…On the Moon and Mercury, the most important of these is photodestruction [ Butler , ], with a characteristic time constant of ∼10 4 –10 5 s. Scaling the solar flux to the orbit of Ceres, we expect a photodestruction timescale ∼10 5 –10 6 s, which is much longer than the timescale of gravitational loss. Indeed, a Monte Carlo model of water molecules in Ceres' exosphere [ Tu et al , ] found a mode dynamical lifetime of ∼10 4 s, very similar to the gravitational escape timescale. Tu et al [] also found that the majority of H 2 O molecules on ballistic trajectories are eventually deposited in the cold traps, with a marked preference for the winter pole.…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, a Monte Carlo model of water molecules in Ceres' exosphere [ Tu et al , ] found a mode dynamical lifetime of ∼10 4 s, very similar to the gravitational escape timescale. Tu et al [] also found that the majority of H 2 O molecules on ballistic trajectories are eventually deposited in the cold traps, with a marked preference for the winter pole.…”

Section: Discussionmentioning

confidence: 99%

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Thermal stability of ice on Ceres with rough topography

2015

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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 (CH 3 OH, NH 3 , SO 2 , and CO 2 ) may be cold trapped in smaller abundances. A model for the transport, gravitational escape, and photoionization of H 2 O 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 > 10 4 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.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Thermal stability of ice on Ceres with rough topography

2015

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“…Half of the output occurs within ± 20 °of the equator. Any water output contributes to a water exosphere ( Formisano et al, 2016;Tu et al, 2014 ). Once a water molecule reaches the surface, it is briefly gravitationally bound, and the density of the exosphere is hence higher than the calculated output rate suggests.…”

Section: Supply To the Exospherementioning

confidence: 96%

Predictions of depth-to-ice on asteroids based on an asynchronous model of temperature, impact stirring, and ice loss

Schörghofer

2016

Icarus

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“…In this way, H 2 O molecules can migrate from any part of the surface to the cold traps [Tu et al, 2014]. In this way, H 2 O molecules can migrate from any part of the surface to the cold traps [Tu et al, 2014].…”

Section: Model Of Water Exosphere and Ice Accumulationmentioning

confidence: 99%

The permanently shadowed regions of dwarf planet Ceres

Schörghofer

Mazarico

Platz

et al. 2016

Geophysical Research Letters

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Ceres has only a small spin axis tilt (4°), and craters near its rotational poles can experience permanent shadow and trap volatiles, as is the case on Mercury and on Earth's Moon. Topography derived from stereo imaging by the Dawn spacecraft is used to calculate direct solar irradiance that defines the extent of the permanently shadowed regions (PSRs). In the northern polar region, PSRs cover ∼1800 km2 or 0.13% of the hemisphere, and most of the PSRs are cold enough to trap water ice over geological time periods. Based on modeling of the water exosphere, water molecules seasonally reside around the winter pole and ultimately an estimated 0.14% of molecules get trapped. Even for the lowest estimates of the amount of available water, this predicts accumulation rates in excess of loss rates, and hence, there should be fresh ice deposits in the cold traps.

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A Sublimation-driven Exospheric Model of Ceres

Cited by 16 publications

References 38 publications

Thermal stability of ice on Ceres with rough topography

Thermal stability of ice on Ceres with rough topography

Predictions of depth-to-ice on asteroids based on an asynchronous model of temperature, impact stirring, and ice loss

The permanently shadowed regions of dwarf planet Ceres

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