Exosphere-mediated migration of volatile species on airless bodies across the solar system

Steckloff, Jordan K.; Goldstein, David; Trafton, Laurence M.; Varghese, Philip L.; Prem, Parvathy

doi:10.1016/j.icarus.2022.115092

Cited by 11 publications

(23 citation statements)

References 181 publications

(226 reference statements)

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“…Both this work and [5] predict very low cold-trapping efficiency for Mercury due to its high irradiation; however, substantial ice deposits have been observed [7,15]. Because our model assumes constant water injection near the subsolar point for all scenarios, this neglects several processes and their subsequent consequences that deliver water to the planet.…”

Section: Discussionmentioning

confidence: 90%

“…Surprisingly, the Moon is perfectly sized for maximum water cold-trapping given its composition and proximity to the Sun.Surface-bound exospheres are very common in the solar system and they are therefore vital for understanding the volatile distribution on these airless bodies. Most studies of volatile transport in an exosphere focus on specific bodies such as the Moon [1-3], Ceres [4], and various outer solar system bodies [5]. There are few parametrical studies of exospheric modelling (e.g.…”

mentioning

confidence: 99%

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The cold-trapping efficiency of water on airless planetary bodies

Nguyen

Kloos

Moores

2023

Preprint

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Many planetoids are airless but despite the lack of a collisional atmosphere, these bodies can experience volatile migration towards the polar regions via the exosphere. Volatiles can then be sequestered at the poles as surface ice cold-trapped in permanently shadowed regions (PSRs). Although cold-trapping plays a role in surface mass distribution and can help to produce transient atmospheres under extreme conditions, there is a lack of parametrical studies that focus on cold-trapping as a general planetary process, as opposed to within the context of specific bodies. Therefore, we run a Monte Carlo simulation to determine the water cold-trapping efficiency for planetoids of varying size, bulk-density, and insolation. We find that small planets lose most of their water via thermal escape while large planets favour photolysis. For a given bulk density and solar irradiation, we find the optimal planetary size where cold-trapping is most efficient. Surprisingly, the Moon is perfectly sized for maximum water cold-trapping given its composition and proximity to the Sun.

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Section: Discussionmentioning

confidence: 90%

mentioning

confidence: 99%

The cold-trapping efficiency of water on airless planetary bodies

Nguyen

Kloos

Moores

2023

Preprint

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“…The rate of deposition on Enceladus varies from ∼10 −6 to ∼10 −3 mm/yr near the equator (Southworth et al., 2019). Using a model for exospheres (Steckloff et al., 2022), and the thermal properties of Enceladus' surface (Howett et al., 2010), we compute the peak insolation‐driven sublimation rate on Enceladus (at the subsolar point), and find that the peak sublimation rate is on the order of ∼10 −20 mm/yr. Thus, accumulation of material on the surface likely dominates over sublimation driven morphologies near the equator on Enceladus.…”

Section: Discussionmentioning

confidence: 99%

“…Callisto, the second largest moon of Jupiter and outermost of the Galilean satellites, contains numerous bright (i.e., high albedo) spires and ridge‐like structures that are proposed to be the result of sublimation/condensation of volatile materials (Howard & Moore, 2008; Moore et al., 1999; Steckloff et al., 2022; White et al., 2016). Qualitatively, this is consistent with the appearance of penitentes.…”

Section: Discussionmentioning

confidence: 99%

Molecular Transport Conditions Required for the Formation of Penitentes on Airless, Ice‐Covered Worlds, With Specific Application to Europa, Enceladus, and Callisto

et al. 2023

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The surface morphology of airless, ice‐covered moons of the outer solar system, such as Europa, Enceladus, and Callisto, is not well known at centimeter‐ to meter‐scales. Ice and snow erode differently on such worlds in part because sublimation is the dominant process. On Earth, ice penitentes have been observed in sublimation‐driven environments, and may provide a guide for similar formations on ice‐covered worlds. Penitentes are blade‐like snow features observed on Earth in high‐altitude, low‐latitude snowfields. Models of penitente formation on Earth break down within the free‐molecular regime of airless bodies, leaving a major gap in understanding whether such morphologies can form on their surfaces. To investigate the morphologic evolution of icy bodies, we developed a Sublimation Monte Carlo (SMC) model that enables a numerical approach to modeling exosphere‐surface interactions at free‐molecular conditions. The SMC model uses Monte Carlo tracking of molecules emitted from the surface to determine the net molecular interchange that drives surface changes. We validated results against experiments, matching the evolution of pre‐formed penitentes as they receded in height and became less pronounced. Our results reveal the importance of molecular redeposition on topology, indicating that the stable morphology of isothermal topographies is a planar morphology on regions of net sublimation, regardless of initial surface shape. A study of parametrically varying temperature profiles for sinusoidal penitentes resulted in the following requirement for penitente growth: the trough temperature must exceed the peak temperature by a threshold value, which notably depends on the surface aspect ratio and peak temperature.

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“…In contrast, this lack of CO 2 ice on Miranda, where radiolytic production of CO 2 molecules should be possible, could result from its small mass and lower efficiency of retaining volatiles like CO 2 . Previous works have extensively discussed potential mechanisms for the production and destruction of CO 2 on the Uranian satellites, such as photolysis or sputtering by charged particles (Grundy et al 2006;Cartwright et al 2015;Sori et al 2017;Steckloff et al 2022). Most importantly, a large fraction of the expected thermal velocity distribution of sputtered or sublimated CO 2 molecules is greater than the escape velocity of Miranda (193 m s −1 ).…”

Section: Co 2 Icementioning

confidence: 99%

Are NH₃ and CO₂ Ice Present on Miranda?

DeColibus,

Chanover,

Cartwright

2023

Planet. Sci. J.

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Published near-IR spectra of the four largest classical Uranian satellites display the presence of discrete deposits of CO2 ice, along with subtle absorption features around 2.2 μm. The two innermost satellites, Miranda and Ariel, also possess surfaces heavily modified by past endogenic activity. Previous observations of the smallest satellite, Miranda, have not detected the presence of CO2 ice, and a report of an absorption feature at 2.2 μm has not been confirmed. An absorption feature at 2.2 μm could result from exposed or emplaced NH3- or NH4-bearing species, which have a limited lifetime on Miranda’s surface, and therefore may imply that Miranda’s internal activity was relatively recent. In this work, we analyzed near-IR spectra of Miranda to determine whether CO2 ice and the 2.2 μm feature are present. We measured the band area and depth of the CO2 ice triplet (1.966, 2.012, and 2.070 μm), a weak 2.13 μm band attributed to CO2 ice mixed with H2O ice, and the 2.2 μm band. We confirmed a prior detection of a 2.2 μm band on Miranda, but we found no evidence for CO2 ice, either as discrete deposits or mixed with H2O ice. We compared a high signal-to-noise-ratio spectrum of Miranda to synthetic and laboratory spectra of various candidate compounds to shed light on what species may be responsible for the 2.2 μm band. We conclude that the 2.2 μm absorption is best matched by a combination of NH3 ice with NH3 hydrates or NH3–H2O mixtures. NH4-bearing salts like NH4Cl are also promising candidates that warrant further investigation.

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Exosphere-mediated migration of volatile species on airless bodies across the solar system

Cited by 11 publications

References 181 publications

The cold-trapping efficiency of water on airless planetary bodies

The cold-trapping efficiency of water on airless planetary bodies

Molecular Transport Conditions Required for the Formation of Penitentes on Airless, Ice‐Covered Worlds, With Specific Application to Europa, Enceladus, and Callisto

Are NH₃ and CO₂ Ice Present on Miranda?

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Exosphere-mediated migration of volatile species on airless bodies across the solar system

Cited by 11 publications

References 181 publications

The cold-trapping efficiency of water on airless planetary bodies

The cold-trapping efficiency of water on airless planetary bodies

Molecular Transport Conditions Required for the Formation of Penitentes on Airless, Ice‐Covered Worlds, With Specific Application to Europa, Enceladus, and Callisto

Are NH3 and CO2 Ice Present on Miranda?

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Are NH₃ and CO₂ Ice Present on Miranda?