Joint Astrophysics/Space Physics Seminar
"The Mars Hydrogen Cycle: Precipitation, Escape, and Aurora" by, Professor Jasper Halekas, Department of Physics & Astronomy, The University of Iowa
Abstract: I will discuss the life and times of hydrogen atoms at Mars, based on the latest greatest observations from MAVEN, Mars Express, and the Hubble Space Telescope. Hydrogen at Mars comes from both above and below, from the solar wind and from the atmosphere. Hydrogen from below is derived from the lower atmosphere and transported to high altitudes to form an extended corona around Mars. Surprising recent observations indicate that the hydrogen abundance in this corona varies by at least an order of magnitude with Martian season. Thanks to Mars' weak gravity, the H corona extends well beyond the bow shock, where it interacts with hydrogen from above in the form of solar wind protons (a.k.a. hydrogen ions). Charge exchange reactions between solar wind and coronal hydrogen create energetic neutral atoms that precipitate into the upper atmosphere. MAVEN has directly observed this hydrogen precipitation for the first time. Better yet, two spacecraft have just reported detections of "proton aurora" UV emissions produced by the interaction of precipitating hydrogen with neutral atoms in the upper atmosphere.