Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
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9 Question 6: Solid Body Atmospheres, Exospheres, Magnetospheres, and Climate Evolution
9 Question 6: Solid Body Atmospheres, Exospheres, Magnetospheres, and Climate Evolution
Pages 246-277
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In this regime, more PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 9-3
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On bodies with surface boundary exospheres, the solar wind and micrometeoroids are directly incident on the surface and are capable of altering surface material to create exospheric volatiles and to influence the cycling of the released volatile species. For example, the solar wind is directly incident at the Moon for three quarters of its orbit and implants protons in the top ~30 nm of grains.
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Changes in the rate of H2O outgassing on Venus can have strong effects on albedo, and hence on climate, through coupling with the sulfur cycle (Bullock PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 9-8
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, has a major impact on much PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 9-9
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Magnetospheres are driven from above by the highly variable solar wind and from below by particles escaping from the planetary atmosphere and ionosphere, with these interactions varying if a planetary magnetic field exists. These upper-atmosphere couplings and interactions have never been fully characterized for any planetary body, thus their full impact remains poorly known.
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Studying present-day atmospheric circulations, surface fluxes, and solar inputs on bodies with differing orbital settings, atmospheric compositions, and surface properties thus provides valuable insight into a huge range of fundamental dynamical processes. This helps us to not only understand the atmospheres of presentday Earth and other solid bodies in our own solar system, but also to extrapolate this knowledge to the past climate states of those bodies (see Q6.1, 6.2)
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For induced magnetospheres, such as those of Mars and Venus, the IMF determines the orientation of the entire magnetosphere. In either case, the magnetosphere is driven both from above by the highly variable solar wind energy, momentum, and electromagnetic fields, and from below by escaping particles from the planetary atmosphere (see Q6.5c)
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, lower-upper atmosphere coupling, atmospheric loss, and martian dust storms, using numerical models. ● Explore the connections between the solar wind, magnetic fields, and the neutral atmosphere/exosphere through numerical modeling.
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Together, they provide natural laboratories for investigating how hydrologic cycles operate and exchange material between atmospheric, surface, and subsurface reservoirs over diurnal, seasonal, and orbital timescales. On airless bodies such as the Moon, Mercury, and Ceres, polar cold traps are of compelling interest to investigations of how volatiles inform the processes of prebiotic chemistry, as well as the history of volatiles throughout the age of the solar system.
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There is circumstantial evidence for ongoing volcanic activity on Venus, including transient thermal emissions from areas of stratigraphically young volcanic deposits and residual heat emitting from young lava flows that lack evidence of weathering. Decadal changes in atmospheric composition suggest that SO2 may be reinjected into Venus' upper atmosphere by major volcanic eruptions, and the presence of a global sulfuric acid cloud is, as on Io, thought to be maintained by continuous volcanic outgassing.
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Over orbital timescales encompassing obliquity and eccentricity cycles, how does the energy balance change, and are polar cap boundaries affected? Q6.4e How Do the Minor Constituents in Planetary Atmospheres Drive the Distribution of Surface and Near-Surface Volatiles, Such as the Distribution of H2O Ice on Mars or CH4 and CO Ices on Triton/Pluto?
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The presence of a magnetic field alters the interaction with the solar wind (Figure 9.5) , reducing the efficiency of some escape processes, but increasing the efficiency of others; however, the net effect of a magnetic field on atmospheric escape remains unquantified.
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Magnetic fields affect charged particle motion and can therefore shield and/or divert charged particle flux from more strongly magnetized regions of the surface. Once liberated from the surface, some exospheric constituents can escape directly to space.
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Yet all three have comparable charged particle escape rates. In the outer solar system, Io, Titan, and Triton are located within giant planet magnetospheres and thus are subject to very different incident plasma than Pluto in the solar wind.
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At Mercury, some portions of the surface routinely experience plasma bombardment, with others only exposed during more extreme solar wind conditions. At the Moon, localized portions of the surface have significant magnetic fields capable of deflecting or reflecting the solar wind.
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magnetospheres. ● Relate the loss of volatiles from surface boundary exospheres to solar wind dynamics and quantify the effects of magnetic fields by measuring escaping, migrating, and bound species in regions of different magnetic topology (e.g., Mercury and Ganymede polar and equatorial regions, lunar magnetic anomalies)
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. The atmosphere of Mars is expected to contain PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 9-24
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. Ionization and dissociation, both by solar radiation and by auroral precipitation of energetic charged PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 9-25
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Q6.6e Do Exospheric Volatile Gases Like H2, CH4, and Water At the Moon, Mercury, and Other Exposed Solid Bodies Result From Regolith-Grain Chemistry That Converts Atomic Species, Like Solar Wind-Implanted Hydrogen and Carbon, Into New Molecules? In the last decade, there has been a new appreciation that oxygen-rich regolith at exposed rocky bodies can act as chemical conversion surfaces that take in material delivered from the solar wind and micrometeoroids and release new surface-manufactured products into the exosphere.
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2016. Contributions of the solar wind and micro‐meteoroids to molecular hydrogen in the lunar exosphere.
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2014. Anisotropic solar wind sputtering of the lunar surface induced by crustal magnetic anomalies.
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