Probing the interior structure of Venus

Stevenson, David J and Cutts, James A and Mimoun, David and Arrowsmith, Stephen and Banerdt, W Bruce and Blom, Philip and Brageot, Emily and Brissaud, Quentin and Chin, Gordon and Gao, Peter and others
{journal}, 2015

The formation, evolution, and structure of Venus remain a mystery more than 50 years after the first visit by a robotic spacecraft. Radar images have revealed a surface that is much younger than those of the Moon, Mercury, and Mars as well as a variety of enigmatic volcanic and tectonic features quite unlike those we are familiar with on Earth. What are the dynamic processes that shape these features, in the absence of any plate tectonics? What is their relationship with the dense Venus atmosphere, which envelops Venus like an ocean? To understand how Venus works as a planet, we now need to probe its interior. Conventional seismology for probing the interior of a planet employs extremely sensitive motion or speed detectors in contact with the planetary surface. For Venus, these sensors must be deployed on the surface and must tolerate the Venus environment (460oC and 90 bars) for up to a year. The dense atmosphere of Venus, which efficiently couples seismic energy into the atmosphere as infrasonic waves, enables two alternatives: detection of these infrasonic waves in the middle atmosphere using a string of two or more microbarometers suspended from a floating platform or detection with an orbiting spacecraft of electromagnetic signatures produced by interactions of infrasonic waves in the Venus upper atmosphere and ionosphere. This report, describing the findings of a workshop, sponsored by the Keck Institute of Space Studies (KISS), concludes that seismic investigations can be successful conducted from all three vantage points—surface, middle atmosphere, and space. Separately or, better still, together, these measurements from these vantage points can be used to transform knowledge of Venus seismicity and the interior structure of Venus. Under the auspices of KISS, a multidisciplinary study team was formed to explore the feasibility of investigating the interior of the planet with seismological techniques. Most of the team’s work was conducted in a five-day workshop held at the KISS facility at the California Institute of Technology (Caltech) campus from June 2–6, 2014. This report contains the key findings of that workshop and recommendations for future work.