A Science Strategy for the Exploration of Europa (1999) / Chapter Skim
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4 Earth-based Studies and Technology Development
4 Earth-based Studies and Technology Development
Pages 41-58
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From page 41... ...
Terrestrial Analogs Below, COMPLEX summarizes categories of terrestrial ice cover that may prove suitable for proof-ofconcept studies for exploring Europa-like environments. Examples include polar and temperate glaciers and ice sheets and ice resting on either bedrock or liquid water.
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From page 42... ...
The dynamical processes manifest themselves on the ice sheet surface by the presence of exotic structures such as ice streams. These are rivers of ice within the ice sheet, hundreds of kilometers long, that discharge ice from the interior ice sheet toward the floating ice shelves and eventually to sea.
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From page 43... ...
EARTH-BASED STUDIES AND TECHNOLOGY DEVELOPMENT 43 FIGURE 4.1 This synthetic-aperture radar image of the confluence of West Antarctic Ice Streams A and B was obtained by the Radarsat-1 spacecraft. Ice Stream A appears vertically oriented in this image.
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From page 45... ...
Consequently, the sea ice has resulted in the misinterpretation of Filchner-Ronne ice thicknesses. The combination of relatively thick fresh ice, the presence of a basal saline ice layer, and an underlying ocean ecosystem suggest that ice shelves are attractive sites for proof-of-concept studies.
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From page 46... ...
· Potential for use of remote sensing (radar) to determine the extent of water; · Requirement for physical penetration of a considerable thickness of ice to access the water; · Application of in situ measurements to determine the chemical and physical properties of the aqueous environment; and · Possible presence of microbiological organisms and the need to practice appropriate planetary protection policies and procedures (lest investigators contaminate the lake, in this case, with surface organisms)
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From page 47... ...
These similarities make the exploration of Lake Vostok an invaluable tool for evaluating and testing techniques for exploring physically buried bodies of water such as might be found on Europa. In situ analysis of the aqueous environment might be accomplished using a cryobot/hydrobot,3 4 a development of the so-called thermal or Philberth probes developed more than 30 years ago for polar and glacial studies on Earth.5 Appropriate measurements to be made of the water would include salinity, pressure exerted by the overlying ice, lightscattering properties, and acidity.
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From page 48... ...
In the case of chemoautotrophs (organisms that gain their energy from chemical reactions) , recent progress has been made in quantifying the geochemical energy available in terrestrial environments if an organism can mediate reactions and take advantage of this energy.l4-l6 Recent progress provides the ability to calculate the thermodynamic data at almost any temperature and pressure of interest.l7-2l What is generally lacking are adequate analytical data appropriate to the environment of interest.
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From page 49... ...
LABORATORY STUDIES Space Weathering of the Surface Materials There is considerable observational evidence that it is necessary to understand space weathering in order to interpret reflectance properties and ages of surface features on Europa. The surface materials are weathered by plasma ions and electrons from the Jovian plasma torus, solar ultraviolet photons, and micrometeorite bombardment, all occurring in the presence of a tenuous oxygen atmosphere that is itself a product of ion bombardment.
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From page 50... ...
Condensed sulfate solids should "sink" within the solution, so it remains enigmatic how such impure systems become sufficiently unstable gravitationally to emerge in the observed dark lineaments on the surface. It may be that systems akin to terrestrial sea ice are a better Europa model, where nearly pure water ice forms a crust on the saline "ocean," increasing the salinity of the underlying liquid in the process.
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From page 51... ...
Although many hydrothermal sulfur redox experiments have been conducted in terrestrial systems, experiments designed to represent processes that can occur in icy satellites are lacking. THEORETICAL STUDIES Thermal History of Europa Previous studies of Europa's thermal history argue convincingly that enough heat is generated by radioactive decay in the rocks inside Europa that separation of rock and metal from water must have occurred early in the evolution of the satellite.
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From page 52... ...
,37 and the europan ocean has been estimated to contain as much as ~0.3 mole % CO2.38 Greater CO2 concentrations would result in plating out of CO2-clathrate at the base of the ocean, which if sufficiently thick might seal the ocean from hydrothermal interaction. Results of theoretical studies of water-rock reactions show that the single most important factor in determining the potential for hydrothermal organic synthesis is the oxidation state imposed by the composition of the rocks that host hydrothermal systems.39 It follows that rigorous constraints on the compositions of the outermost layer of silicates, and their influence on the compositions of hydrothermal fluids, are major determinants in testing the potential for hydrothermal organic synthesis on Europa.
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From page 53... ...
Consequently, and perhaps at different times, the surface of Europa may have behaved somewhat like terrestrial ice sheets and sea ice cover. More enigmatic are the banded ridges running for hundreds of kilometers across the surface.
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From page 54... ...
Moreover, the procedures to enable tracking of solar system objects were not in place when the Hubble Space Telescope was launched, and work over several years was required to implement this capability. HST can now observe Europa relatively easily using linear approximations of the actual non-linear tracking rates.
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From page 55... ...
EARTH-BASED STUDIES AND TECHNOLOGY DEVELOPMENT 55 FIGURE 4.6 A Galileo image of Europa showing the size of the diffraction-limited resolution elements that can be obtained at a wavelength of 2 microns using a 10-m, ground-based telescope equipped with active optics. Image courtesy of M
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From page 56... ...
: · Low-mass, radiation-hardened instrumentation to be used on orbiting spacecraft and on surface-deployed packages (including landers, rovers, and penetrators) ; · Low-mass, compact-size, wavelength-tunable radar systems, or other subsurface remote-sensing systems, with a broad range of capabilities for measuring the thickness and structure of an ice layer with unknown and poorly constrained dielectric and mechanical properties; · High-capacity communications to enable sophisticated application of microscopic and spectroscopic imaging techniques; · Robotic systems capable of physically penetrating through substantial thicknesses of ice that may contain some unknown fraction of admixed rock with unknown size distnbution; · Robotic systems capable of in situ study of the organic chemistry and, perhaps, biochemistry of deep ice cores andlor subsurface liquid water; · Robotic systems capable of reaching and exploring a subsurface layer of liquid water; and · Robotic systems capable of returning samples of deep ice cores andlor subsurface liquid water to Earth.
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From page 57... ...
Knox, and L Richard, "Calculation of the Standard Molal Thermodynamic Properties of Crystalline, Liquid, and Gas Organic Molecules at High Temperatures and Pressures," Geochemica et Cosmochemica Acta 62: 985, 1998.
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From page 58... ...
Schulte, and W.B. McKinnon, "Coupled Organic Synthesis and Mineral Alteration in Hydrothermal Systems on Europa," Europa Ocean Conference, San Juan Capistrano Research Institute, San Juan Capistrano, California, 1996, page 63.
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