between these events for each of the inner planets is possible if noble gas isotopic ratios can be measured with a state-of-the-art neutral mass spectrometer. Previous spacecraft measurements have been inadequate to address these issues. VISE will determine the noble gas abundances and isotope ratios to sufficient accuracy to distinguish between hypotheses of the origin and evolution of Venus’s atmosphere. A meteorological package will measure atmospheric pressure and temperature profiles down to the surface, and pressure, temperature, and winds at the surface. Cloud-level winds will be determined by tracking the ascent balloon during its 3.5-day lifetime, providing improved data on atmospheric dynamics and the origin of Venus’s mysterious atmospheric superrotation.


Surface Science Objectives:


The former Soviet Union’s Venera landers returned basic elemental chemistry and images of four sites on the surface, and Magellan data provided evidence of possible evolved volcanic deposits. However, we lack sufficient information on surface elemental abundances and mineralogy to determine the degree of crustal evolution on Venus. The VISE mission would measure elemental compositions at a surface site complementary to those of the Veneras. Mineralogy of a surface sample core will be obtained for the first time, allowing analysis of any weathered layer and testing for depth of alteration and occurrence of unaltered material. Textural analysis of the sample using a microscope imaging system would provide information on the formation and nature of surface rocks. These data will be used to constrain questions outlined above. Despite global radar coverage of Venus by Magellan, little is known of the surface morphology at scales of 1 to 10 m. Without such information, it is difficult to determine how the plains formed and to understand the nature of mobile materials on the surface. A descent camera on the lander will provide the first broadscale visible images of the surface, with images returned from about 10 km altitude to the surface. These images will enhance interpretation of the Magellan radar images by providing ground-truth data on the surface texture of the lava flows that make up Venus’s plains. The morphology and texture of these flows can be related to emplacement rate, volatile content, and rheology, which are needed in order to understand the role of volcanism in shaping the atmosphere and surface of Venus. Images of Venus’s surface will also be returned from the lander, with filters chosen to provide compositional information. These images will help to determine the recent geological history of Venus and will resolve differences in the interpretation of Venus’s resurfacing history.

Developments Since the Decadal Survey

Since the decadal survey, NASA’s Venus Exploration Analysis Group (VEXAG) has worked with the Venus science community to develop the following Venus exploration goals, with prioritized objectives.11


Goal 1: Origin and Early Evolution of Venus: How did Venus originate and evolve?


The highest priority objectives are:

  1. Determine the elemental and isotopic composition of the atmosphere to identify earlier epochs of Venus’s history, and clues to Venus’s origin, formation and evolution.

  2. Map the mineralogy and chemical composition of Venus’s surface on the planetary scale for evidence of past environmental conditions and for constraints on the evolution of Venus’s atmosphere.

11

The committee has reproduced only the top three VEXAG goals but notes that the VEXAG committee has produced a valuable document that can be used as a reference on Venus science objectives. This document, Venus Exploration Goals, Objectives, Investigations, and Priorities: 2007, is available at http://www.lpi.usra.edu/vexag/vexag_goals_2007.pdf.



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