• Characterize a large lunar impact basin through “ground truth” validation of global, regional, and local remotely sensed data of the sampled site;

  • Elucidate the sources of thorium and other heat-producing elements to understand lunar differentiation and thermal evolution; and

  • Determine the age and composition of farside basalts to determine how mantle source regions on the Moon’s farside differ from the basalts from regions sampled by Apollo and Luna.

VENUS IN SITU EXPLORER

A Venus In Situ Explorer mission would address fundamental unanswered questions of the history and current state of Venus through a characterization of the chemical composition and dynamics of the atmosphere of Venus, and/or measure surface composition and rock textures. While it is unlikely that all of the objectives delineated in the decadal survey could be addressed within the New Frontiers cost constraints, a mission that addresses a subset of these objectives would provide critical information about the present state and history of Venus. The current European Space Agency (ESA) Venus Express mission has greatly expanded knowledge of the upper atmosphere and exosphere of Venus, and has contributed to understanding of regions of the atmosphere nearer to the planet’s surface. However, characterization of the noble-gas and isotopic signatures of the well-mixed lower atmosphere would greatly expand understanding of the formation and evolution of the atmosphere of Venus, illuminate important elements of the current climate, including the drivers for the Venus greenhouse effect, and potentially provide insight on the early tectonic evolution of the planet. Prior landed missions of Soviet Venera and Vega spacecraft (Figure 2.2) have provided some information on crustal compositions and textures, but they have been confined to lowland areas composed of basaltic lava flows. Landed missions in highland regions or on older terrains could answer questions related to presence of silicic rock compositions or earlier phases of tectonism, but they present significant technological challenges.

FIGURE 2.2 Image taken of the surface of Venus by Venera 13 in 1982. The Soviet Union successfully conducted several Venus lander missions with 1980s era technology. These images depict the distorting effects of the thick Venusian atmosphere. SOURCE: C.M. Pieters, J.W. Head, W. Patterson, S. Pratt, J.B. Garvin, V.L. Barsukov, A.T. Basilevsky, I.L. Khodakovsky, A.S. Selivanov, A.S. Panfilov, Y.M. Getkin, and Y.M. Narayeva, The color of the surface of Venus, Science 234:1379-1383, 1986. Reprinted with permission of AAAS.



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