Atmospheric Escape at Mars and Venus: Past, Present and Future
When
Where
Dr. Shannon Curry
Assistant Deputy Director of Planetary Science, Space Sciences Laboratory
University of California, Berkeley
Earth, Venus and Mars formed at similar times, yet their atmospheres have evolved drastically differently. Geophysics and geology play a major part in that, however the influence of the Sun and its evolution on planetary atmospheres is often overlooked. So how is atmospheric escape at different at Venus and Mars? Both Venus and Mars lack a global dipole magnetic field, which can expose their atmospheres to scavenging more so than a planet like Earth. At Mars, photochemical escape is currently the main channel for atmospheric escape; this is the process where molecules are photodissociated and obtain enough energy to exceed the escape velocity. However, Venus is roughly seven times more massive than Mars, and subsequently its gravitational well impedes photochemical escape. So at Venus, as opposed to Mars, virtually all significant present day atmospheric escape of heavy constituents is in the form of ions.
To this end, I will discuss past observations of Mars and Venus atmospheric escape throughout solar cycle 22, 23 and 24. I will also discuss present day observations of escape from the Parker Solar Probe (PSP) Venus flybys. I will compare the Venusian picture of atmospheric escape to that at Mars by presenting Mars Atmosphere and Volatile Evolution (MAVEN) observations of the Martian atmosphere and solar drivers, such as flares and coronal mass ejections. Using a composite of in-situ observations at Mars and Venus, I will discuss a global picture of atmospheric evolution throughout the last three solar cycles. Finally, I will present extrapolations of these results back in time when our sun was younger and more active, serving as an analogue for other stellar systems with exoplanets.