Exploring Organic Environments in the Solar System (2007) / Chapter Skim
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5 The Giant Planets and Their Satellites
5 The Giant Planets and Their Satellites
Pages 72-84
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From page 72... ...
Jupiter's icy satellites Ganymede, Callisto, and especially Europa each show evidence of layers of liquid water that offer potentially uniquely interesting environment for organic synthesis. These bodies are also subject to intense radiation bombardment at their locations within Jupiter's magnetosphere that can potentially affect carbon chemistry in the surface and near-surface ices.
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From page 73... ...
Spectra also indicate CO2, and its spectral characteristics suggest that it is trapped within or bound to dark surface materials. A broad absorption in the ultraviolet is suggestive of trapped O3 and another unidentified band that may be the CH2O functional group of an organic compound.5 Carbon dioxide shows interesting and suggestive correlations with both albedo and topography in the three icy Galileans.
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From page 74... ...
Titan In terms of organic chemistry, the premiere destination within the solar system is Saturn's Mercury-sized satellite Titan. Its 1.5-bar atmosphere contains about 98 percent nitrogen and about 2 percent methane and more complex hydrocarbons.
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From page 75... ...
, CO, and H2O. Ground-based mutual satellite occultation data and modeling, as well as more recent Hubble Space Telescope observations, show broad-scale albedo variations on Pluto's surface, providing evidence for dark material in its equatorial regions.
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From page 76... ...
Most photochemical models are one-dimensional approximations, and only recently have some models attempted to deal with two-dimensional approximations.28 A follow-up mission to Titan, for example, should be equipped to study the three-dimensional distribution of a variety of organics through both remote sensing and direct sampling of the atmosphere. Laboratory studies may also be conducted under simulated outer solar system conditions, and photolytic products can be studied directly in the laboratory.29 Radiogenic and Tidal Heating The Galileo orbiter made numerous close flybys of each of Jupiter's large icy satellites, Europa, Ganymede, and Callisto.
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From page 77... ...
Reprinted with permission of the American Astronomical Society. environments that are conducive to complex carbon chemistry.
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From page 78... ...
The suggestion of a global ocean appears to be inconsistent, however, with existing observational data.38-41 Currently, these observations (from ground-based radar, near-infrared, and the Hubble Space Telescope) , taken together, suggest that liquid-phase hydrocarbons on Titan's surface are certainly not global but may exist in craters;42 a supposition now potentially confirmed by Cassini's radar observations.43 If liquid-phase hydrocarbons on Titan's surface are not sufficient to resupply methane at a steady-state level, it has also been proposed that perhaps Titan is currently in an unusual epoch in its history in which its atmosphere is in an unusually dense state that will eventually become less dense like those found around Triton and Pluto.44 If such a scenario is true, layered deposits of organics on Titan's surface may preserve a record of these events that would be accessible to advanced missions that might follow Cassini/Huygens.45 Solid-State Greenhouse The Voyager flyby of Neptune and Triton in 1989 revealed the presence of plumes of dark material rising approximately 8 km in the atmosphere, with dark material subsequently blown 100 km downwind leaving surface streaks.
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From page 79... ...
The Europa Geophysical Explorer, a somewhat more elaborate version of the Europa Orbiter, was the highest-priority large mission recommended by the 2003 solar system exploration decadal survey.53 NASA responded to the survey's recommendation by initiating the development of JIMO, the Jupiter Icy Moons Orbiter mission, the first of a series of advanced-technology spacecraft employing nuclear-electric propulsion systems that would have significantly expanded scientific capabilities compared with previous Europamission concepts. JIMO would have conducted global orbital mapping surveys of all three icy satellites, at resolutions of 10 m or better, and might have included a small Europa lander.
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From page 80... ...
This fact can be viewed as both a disadvantage and an advantage. Nevertheless, the relative simplicity of the complex reaction schemes in the atmospheres of the giant planets serves as a test to both understand and model such systems, which may also suggest important conditions for organic synthesis in other reducing environments.
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From page 81... ...
, Cambridge University Press, 2004. Copyright 2004.
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From page 82... ...
McKinnon, eds.) , Cambridge University Press, Cambridge, England, 2004.
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From page 83... ...
34. See, for example, National Research Council, Priorities in Space Science Enabled by Nuclear Power and Propulsion, The National Academies Press, Washington, D.C., 2006, pp.
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From page 84... ...
54. National Research Council, Priorities in Space Science Enabled by Nuclear Power and Propulsion, The National Academies Press, Washington, D.C., 2006, pp.
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