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From page 235... ... 9 Question 6: Solid Body Atmospheres, Exospheres, Magnetospheres, and Climate Evolution What establishes the properties and dynamics of solid body atmospheres and exospheres, and what governs material loss to and gain from space and exchange between the atmosphere and the surface and interior? Why did planetary climates evolve to their current varied states? Read the entire page →
From page 236... ... 236 ORIGINS, WORLDS, AND LIFE FIGURE 9-1 Overview of atmospheric characteristics for the solid planets and moons discussed in this chapter. Top panel: Bodies with collisionless exospheres only. Read the entire page →
From page 237... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 237 These are but a few of a fascinating array of questions that remain to be answered about the atmospheres of the planets and moons in today's solar system. The committee highlights the major outstanding issues below. Read the entire page →
From page 238... ... 238 ORIGINS, WORLDS, AND LIFE the young Sun would have made this process particularly important to atmospheric evolution in the first few hundred million years after the planets formed (Lammer et al. Read the entire page →
From page 239... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 239 early atmosphere, and this may help explain why Mars's early climate was relatively warm despite the faintness of the young Sun (Ramirez et al. Read the entire page →
From page 240... ... 240 ORIGINS, WORLDS, AND LIFE • Develop physical and chemical constraints on early atmosphere–interior exchange by performing laboratory experiments on volatile partitioning in silicate melts, meteorite shock chemistry, and related phenomena. Read the entire page →
From page 241... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 241 during the ensuing Proterozoic and Phanerozoic eons is a research topic of great interest to astrobiologists because it is poorly understood and because it is relevant to the question of whether O2 is a good biomarker on extrasolar planets (see Question 12, Chapter 15) Read the entire page →
From page 242... ... 242 ORIGINS, WORLDS, AND LIFE between samples of ancient Mars (in returned rock samples and meteorites) and the present-day atmosphere provides information on atmospheric source and sink processes over time. Read the entire page →
From page 243... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 243 • Constrain the timing of martian climate transitions by performing geochronological dating of samples from multiple locations on the planet's surface. • Constrain atmospheric evolution processes on Mars by returning samples of the atmosphere to Earth of sufficient concentration and fidelity to allow noble gas abundance and isotopic fractionation to be measured. Read the entire page →
From page 244... ... 244 ORIGINS, WORLDS, AND LIFE FIGURE 9-3 Processes influencing solid body collisional atmospheres, including interior-surface-atmosphere and solar environment interactions. Note that the relative heights of where processes are shown to occur are not drawn to scale. Read the entire page →
From page 245... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 245 angular-momentum gradient. Yet while mechanisms for driving this have been proposed, most of the atmospheric waves involved have not been observed. Read the entire page →
From page 246... ... 246 ORIGINS, WORLDS, AND LIFE in the thick clouds produce significant albedo variations (hence amount of solar energy absorbed) on decennial timescales, potentially modifying superrotation (Pérez-Hoyos et al. Read the entire page →
From page 247... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 247 but it remains unclear if surface formation/release, transport, and sequestration/trapping of volatiles are universal processes across all exosphere-only rocky bodies. Strategic Research for Q6.3 • Determine how atmospheric waves drive atmospheric dynamics and energetics, especially phenomena such as supperrotation and lower-upper atmosphere coupling by observing wave amplitudes, periods, phases, and spatiotemporal distributions in thermal and direct wind measurements over multiple annual cycles on Venus, Mars, and Titan. Read the entire page →
From page 248... ... 248 ORIGINS, WORLDS, AND LIFE FIGURE 9-4 (a) Dynamic clouds on Venus as seen in composite Akatsuki UVI camera images. Read the entire page →
From page 249... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 249 Observations of surface changes caused by aeolian processes often constitute our only information on near-surface wind patterns and environmental conditions. The composition of volatile species in planetary atmospheres drives the formation, evolution, and stability of ices across planetary surfaces. Read the entire page →
From page 250... ... 250 ORIGINS, WORLDS, AND LIFE Q6.4c What Can Aeolian Features and Their Temporal Variation Tell Us About Near-Surface Winds and Other Atmospheric Variables? What Are the Mechanisms That Connect Wind-Driven Surface Modifications to Environmental Conditions? Read the entire page →
From page 251... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 251 Q6.4f What Do the Present-Day Methane Cycle on Titan and Past Water Cycle(s) on Mars Tell Us About How Hydrologic Cycles Operate and Exchange Material Between Surface and Atmospheric Reservoirs? Read the entire page →
From page 252... ... 252 ORIGINS, WORLDS, AND LIFE FIGURE 9-5 Atmospheric escape processes. Those on the left act on unmagnetized planets; those on the right act on magnetized planets. Read the entire page →
From page 253... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 253 FIGURE 9-6 Multiple processes contribute to the formation and evolution of surface-boundary exospheres. Source terms include both endogenic processes such as natural radioactivity in the crust and outgassing/plumes from localized regions, and exogenic processes such as photon, micrometeoroid, and charged particle bombardment. Read the entire page →
From page 254... ... 254 ORIGINS, WORLDS, AND LIFE Q6.5a How Does the Presence or Absence of Intrinsic or Parent Body Magnetic Fields Influence the Escape of Gases from Solid Planets and Satellites? The hypothesis that a global magnetic field shields the atmosphere from solar wind-driven loss processes seems intuitively obvious, as the solar wind plasma and its electromagnetic fields cannot then interact directly with the upper atmosphere. Read the entire page →
From page 255... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 255 mass loading in the extended exosphere that transfers momentum from the upstream solar wind, remains poorly quantified and may vary significantly with, for example, object size and solar inputs. For bodies with intrinsic magnetic fields, such as Earth (Toledo-Redondo et al. Read the entire page →
From page 256... ... 256 ORIGINS, WORLDS, AND LIFE • Reveal the factors that control the structure, composition, and dynamics of surface boundary exospheres (e.g., Mercury, Moon, Ceres, and Europa) by simultaneously measuring energetic inputs and escaping species for at least one orbit and preferably for a substantial portion of the solar cycle. Read the entire page →
From page 257... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 257 FIGURE 9-7 Temperature profiles on three terrestrial planets and one moon, all of which have relatively dense atmospheres. Condensation clouds are present on Earth and Mars, photochemical haze is present on Venus, and Titan has both. Read the entire page →
From page 258... ... 258 ORIGINS, WORLDS, AND LIFE detection limits of either the rover or the orbiter (Webster et al. Read the entire page →
From page 259... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 259 atomic hydrogen and other light species is critically dependent. Ion-neutral chemistry is another key process in the interaction of the neutral atmosphere and exosphere with the ionosphere. Read the entire page →
From page 260... ... 260 ORIGINS, WORLDS, AND LIFE • Constrain the photochemical paths that take methane to more complex hydrocarbons in methane rich atmospheres (primarily Titan, but also including Triton, Pluto, and other KBOs) by measuring the composition of hazes and aerosols in the atmosphere and on the surface. Read the entire page →
From page 261... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 261 Gronoff, G., P Arras, S Read the entire page →
From page 262... ... 262 ORIGINS, WORLDS, AND LIFE Kivelson, M.G., and F Bagenal. Read the entire page →
From page 263... ... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 263 Siegler, M.A., R.S. Miller, J.T. Read the entire page →
From page 264... ... Q7 PLATE: One of the poles of Jupiter, as imaged by the JunoCam instrument onboard the Juno spacecraft in 2019. SOURCE: Courtesy of NASA/JPL-Caltech/SwRI/MSSS/G. Read the entire page →

From page 235...

... 9 Question 6: Solid Body Atmospheres, Exospheres, Magnetospheres, and Climate Evolution What establishes the properties and dynamics of solid body atmospheres and exospheres, and what governs material loss to and gain from space and exchange between the atmosphere and the surface and interior? Why did planetary climates evolve to their current varied states?