[IGPP Everyone] Space Physics Seminar, Fri. 2/23 3:30pm: "Cold Ion Outflow and Magnetic Topology in Mars’ Magnetotail" (D. Mitchell UCB SSL)

[Emmanuel V. Masongsong]

SPACE PHYSICS SEMINAR 
DEPARTMENT OF EARTH, PLANETARY, AND SPACE SCIENCES 


DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES 

UNIVERSITY OF CALIFORNIA, LOS ANGELES 



Cold Ion Outflow and Magnetic Topology in Mars’ Magnetotail 



David Mitchell 
UC Berkeley, Space Sciences Lab 



The enhancement of heavy isotopes in Mars’ atmosphere indicates that loss of atmosphere to space has played an important role in transforming the planet’s climate. This loss can take place through a variety of mechanisms, and has been aided by a weak gravity and the cessation of a global magnetic field ~4 Ga ago. Jeans escape for hydrogen and photochemical escape for oxygen appear to be the dominant loss processes today; however, ion outflow down the tail might contribute significantly. Ion outflow can take place through several processes, depending on the magnetic configuration and the acceleration mechanism (ambipolar, V x B and J x B electric fields, as well as wave heating). Magnetic topology plays an important role, since the configuration of Mars’ magnetotail is complex and dynamic, and access to a dense source of planetary ions significantly affects the loss rate. Estimates of the total oxygen ion loss down the tail have increased tenfold over the past 10 years, largely as a result of measuring and including lower energy ions in the calculation. Measuring the escape flux from ~10 eV down to the escape energy (~4 eV for O2+) is especially difficult, because corrections for spacecraft motion and spacecraft charging are large. Since August 2016, the Mars Atmosphere and Volatile EvolutionN (MAVEN) spacecraft has been conducting a series of observing campaigns designed to measure cold ion outflow down to escape energy. As the orbit precesses and sweeps through the tail, the spacecraft reorients from 1200 to 5000 km altitude to optimize the fields of view for the Supra-Thermal and Thermal Ion Composition (STATIC) instrument and the Solar Wind Electron Analyzer (SWEA). Data from SWEA and the Magnetometer (MAG) are used to determine the magnetic field topology, and in particular whether field lines are open, closed, or draped, and if open or deeply draped whether they have access to the day-side or night-side ionosphere. STATIC, SWEA, and the Langmuir Probe and Waves (LPW) experiment determine the spacecraft potential throughout the Mars environment using multiple, cross-calibrated methods. Simultaneous observations by STATIC are used to measure the density, composition, and velocity of planetary ions on these same field lines, all corrected for spacecraft motion and spacecraft potential. Combining data from four sweeps of MAVEN's orbit through the tail (~600 orbits), we have built up a database from which we can map statistics and develop a picture of ion outflow in Mars' tail. 



Friday, February 23, 2018 

Room 6704 Geology 

3:30 - 5:00 PM 



In Charge: 

V. Angelopoulos 


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