Speaker: Robert Lillis (SSL/Berkeley)
Talk title/abstract: MAVEN and the mysterious disappearance of Mars' atmosphere
Why is the surface of Mars no longer habitable? Sounds like a straightforward question, right? However, those nine words comprise one of the most vexing questions in planetary science. There is now overwhelming evidence from orbiters and rovers that Mars was once a place where liquid water flowed on the surface and, thus, life as we know it could have thrived, at least episodically. However, such stable surface water requires an atmospheric surface pressure much higher than today’s ~7 millibars (<1% of Earth’s pressure) to prevent evaporation and cause greenhouse warming. Where did this ancient atmosphere go? If it had all been absorbed back into the crust, abundant carbonate minerals should exist on or near the surface. However, extensive surveys from orbit have revealed not nearly enough carbonate to account for all the carbon dioxide that has been lost. The only other explanation: The atmosphere escaped out to space over billions of years. But how did this happen? What physical processes drove the escape? How did they vary over time as solar radiation and the solar wind buffeted Mars’ atmosphere, which lacked the protection of a global magnetic field? And, most importantly, how much total atmosphere escaped over Mars’ history? These are the questions that motivate the MAVEN team’s scientific efforts—day in and day out—as we analyze and interpret data from our nine science instruments. Our overarching strategy is to use MAVEN’s observations to understand the processes that cause atmosphere to escape out into space, as they operate under the conditions experienced by present-day Mars. We will then combine that with knowledge of how those conditions have varied over time to estimate the total loss of atmosphere. Sounds simple, right? But as always, and as you probably guessed, the devil is in the details. I will present an overview of scientific results from the first three years of the MAVEN mission to Mars, with an emphasis on atmospheric loss processes and how these have transformed the Martian climate over time.