Ices on Mercury: Chemistry of volatiles in permanently cold areas of Mercury's north polar region

Delitsky, M. L.; Paige, D. A.; Siegler, M. A.; Harju, Ellen R.; Schriver, D.; Johnson, R. E.; Trávníček, Pavel

doi:10.1016/j.icarus.2016.08.006

Cited by 27 publications

(27 citation statements)

References 127 publications

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“…In Figure a, the model predicts that more flux precipitates to the lunar polar regions and less to the equatorial region for all three paleofield strengths compared to the unmagnetized case (0 μT, black curve). Such a pattern is comparable to that predicted and observed at Mercury (Delitsky et al, ; Massetti et al, ; Raines et al, ). Furthermore, greater surface precipitation is observed in the polar regions for higher paleomagnetic field strength (i.e., the 5‐μT case shows the most flux to the polar regions) as the paleo‐magnetosphere cusp regions funnel relatively more flux to the poles.…”

Section: Paleo‐magnetosphere Resultssupporting

confidence: 90%

“…If most of the Moon was shielded from H + implantation due to a dynamo field, solar wind water production and polar accumulation could have been arrested. In contrast, if the ancient dynamo drove solar wind particles to precipitate into polar regions, the local weathering rates of any exposed ices could have been enhanced, as suggested for Mercury (Delitsky et al, 2017). To investigate and potentially elucidate some of these competing effects, we have simulated two dynamo field geometries (dipoles perpendicular and parallel to the lunar spin axis) and three different equatorial surface field strengths (0.5, 2, and 5 μT).…”

Section: Introductionmentioning

confidence: 99%

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The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

Garrick‐Bethell

Poppe

Fatemi

2019

Geophysical Research Letters

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Analyses of lunar samples suggest the Moon once possessed a dynamo from ~4.25 Ga until perhaps as recently as 1 Ga, with surface field strengths between ~5 and 100 μT. While the exact timing, strength, and structure of these paleomagnetic fields are not precisely known, such relatively strong fields imply that the Moon also likely possessed a magnetosphere. Here, we present hybrid plasma simulations of the structure and morphology of the putative lunar “paleo‐magnetosphere” for varying surface field strengths and orientations, using ambient solar wind conditions representative of the early Sun. The presence of the paleo‐magnetosphere reduces total solar wind fluxes to the lunar surface overall yet, for a spin‐aligned dynamo, increases the relative solar wind flux to the lunar polar regions. In turn, the paleo‐magnetosphere may have altered the rate of volatile accretion to the Moon over its history.

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Section: Paleo‐magnetosphere Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

Garrick‐Bethell

Poppe

Fatemi

2019

Geophysical Research Letters

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“…Many of Mercury's radar‐bright ice deposits are covered by a layer of low‐reflectance material that has been interpreted to be the carbonaceous leftovers of ice that has sublimated or “thermal lag” (Crites et al, ; Delitsky et al, ; Neumann et al, ; Paige et al, ; Syal et al, ). MESSENGER neutron data and thermal models show that these low albedo lag deposits are up to 10–30 cm thick (Lawrence et al, ; Paige et al, ), and images indicate that the low‐reflectance deposits directly overlie ice deposits, terminating sharply at the boundary of radar‐bright regions (Chabot et al, ).…”

Section: Discussionmentioning

confidence: 99%

Impact Gardening as a Constraint on the Age, Source, and Evolution of Ice on Mercury and the Moon

et al. 2020

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We update an analytic impact gardening model (Costello et al., 2018, https://doi.org/10.1016/j.icarus.2018.05.023) to calculate the depth gardened by impactors on the Moon and Mercury and assess the implications of our results for the age, extent, and source of water ice deposits on both planetary bodies. We show that if the water presently on the Moon has a primordial origin, it may have been 4–15 m thick. If ice deposits are buried, they may be as shallow as 3 cm or as deep as 10 m and provide a gradient of probability for ice gardened into a column. Our calculations for gardening on Mercury show that thermal lag deposits will be reworked into the background over 200 Myr, and, thus, the most recent large‐scale deposition of ice on Mercury must have occurred no more than 200 Myr ago. We also find that gardening mixes incremental layers of ice with underlying regolith and prevents the growth of pure ice deposits by continuous supply. We conclude that ice deposits on the Moon and Mercury are likely the result of sudden and voluminous deposition.

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“…For example, the water at Mercury may have been supplied by a recent comet impact, and no such comets may have hit the Moon in the geologically recent past. Further, even if there is recent and/or ongoing volatile deposition, different processes could still be affecting the resulting deposits in different ways [ Delitsky et al ., ]. So while there is information pointing at all these explanations as possible explanations, we currently do not have enough information to definitively resolve why there is the difference between the PSRs at the Moon and Mercury.…”

Section: Why Are the Moon And Mercury's Psr Volatiles So Different?mentioning

confidence: 90%

“…In a recent study, Delitsky et al . [] suggested that the dark, carbon‐rich material may be dominantly formed by energetic protons and electrons focused to the polar regions by Mercury's magnetic field.…”

Section: Timeline Of Psr Explorationmentioning

confidence: 99%

A tale of two poles: Toward understanding the presence, distribution, and origin of volatiles at the polar regions of the Moon and Mercury

Lawrence

2017

JGR Planets

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The Moon and Mercury both have permanently shaded regions (PSRs) at their poles, which are locations that do not see the Sun for geologically long periods of time. The PSRs of the Moon and Mercury have very cold temperatures (<120 K) and as a consequence act as traps for volatile materials. Volatile enhancements have been detected and characterized at both planetary bodies, but the volatile concentrations at Mercury's poles are significantly larger than at the Moon's poles. This paper documents the study of PSR volatiles at the Moon and Mercury that has taken place over the past 60 years. Starting with speculative ideas in the 1950s and 1960s, the field of PSR volatiles has emerged into a thriving subfield of planetary science that has significant implications for scientific studies of the solar system, as well as future human exploration of the solar system. While much has been learned about PSRs and PSR volatiles, many foundational aspects of PSRs are still not understood. One of the most important unanswered questions is why the PSR volatile concentrations at the Moon and Mercury are so different. After describing the initial predictions and measurements of PSR volatiles, this paper documents a variety of PSR measurements, summarizes the current understanding of PSR volatiles, and then suggests what new measurements and studies are needed to answer many of the remaining open questions about PSR volatiles.

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Ices on Mercury: Chemistry of volatiles in permanently cold areas of Mercury's north polar region

Cited by 27 publications

References 127 publications

The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

Impact Gardening as a Constraint on the Age, Source, and Evolution of Ice on Mercury and the Moon

A tale of two poles: Toward understanding the presence, distribution, and origin of volatiles at the polar regions of the Moon and Mercury

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