1. Characterize the history of volatiles in the interior, surface and atmosphere of Venus, including volatile additions due to cometary impacts, degassing and atmospheric escape, to understand the planet’s geologic and atmospheric evolution.

Goal 2: Venus as a Terrestrial Planet: What are the processes that have shaped and still shape the planet?

The highest priority objectives are:

  1. Constrain the coupling of thermochemical, photochemical and dynamical processes in Venus’s atmosphere and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles.

  2. Constrain the resurfacing history of Venus, and the nature of the resurfacing processes, including the role of tectonism, volcanism, impacts of asteroids or comets, sedimentation/erosion, and chemical weathering.

  3. Constrain the nature and timing of volcanic activity on Venus, including thermal evolution, current and past rates of volcanic activity, and the effects of outgassing on atmospheric and interior processes.

Goal 3: What does Venus tell us about the fate of Earth’s environment?

The highest priority objectives are:

  1. Search for evidence of past global-climate changes on Venus, including chemical-and-isotope evidence in the atmosphere, as well as rock chemistry and characteristics of surface weathering. In particular, seek evidence for the presence or absence of past oceans.

  2. Search for evidence of past changes in interior dynamics, volcanics and tectonics, including possible evolution from plate tectonics to stagnant-lid tectonics, which may have resulted in significant changes in the global climate pattern.

  3. Characterize the Venus greenhouse effect, including the interplay of chemistry, dynamics, meteorology, and radiative physics in the atmosphere, especially in the clouds.

In addition, ESA’s Venus Express has entered Venus orbit and has returned new data since the decadal survey. Venus Express has expanded understanding of the upper atmosphere and exosphere and has contributed to knowledge of the mid- to lower atmosphere. However, most of the science objectives from the decadal survey require in situ measurements that are beyond the capabilities of an orbital mission such as Venus Express.12


The committee concludes that a VISE mission remains a very scientifically important mission that should be considered for the New Frontiers Program. The VEXAG goals and objectives align well with the New Frontiers Venus mission objectives, further validating the selection process in the decadal survey. Although these objectives address fundamental science themes for Venus exploration, it is unlikely that they can be fully addressed in a single mission. Cost and technology risk factors may preclude a single VISE mission proposal from addressing all of the objectives. Consequently, a mission that addresses a major subset of the objectives would be consistent with the recommendations of the decadal survey. For example, a successful mission might not have to include a landed component if it addressed the major atmospheric objectives. In addition, an interpretation of the decadal survey’s science objectives should prescribe the important data to be collected, rather than dictate measurement techniques or mission scenarios. While no attempt is made here to prescribe or define implementation strategies, potential challenges related to the Venus environment—such as high temperatures, high pressures, and a corrosive atmosphere in the near-surface environment—may require the use of nontraditional (though previously demon-


New Frontiers in the Solar System, p. 58.

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