Magnetic Planets and How Mars Lost Its Atmosphere Bob Lin Physics Department & Space Sciences Laboratory Universityyf of Calif ornia, Berkeley Also (visiting) School of Space Research Kyung Hee University, Korea Thanks to the MGS, MAVEN, and LP teams Earth’s Magnetic Field The Earth’s Magnetosphere Explorer 35 (1967) Lunar Shadowing Apollo 15 Mission -1971 Lunar Rover -> <- Jim Arnold's Gamma-ray Spectrometer <- Apollo 15 Subsatellite -> <= SIM (Scientific Instrument Module) Lunar Shadowing <= Downward electrons <= Upward electrons <= Ratio of Upward to DdltDownward electrons Electron Reflection Electron Trajectory Converging Magnetic Fields Secondary Electron ---- ---- - dv||RemotelydU SensingdB Surface MagneticB Fields by m + e + μ = 0⇒sin 2 α = LP []1- eΔU E Planetary Electron Reflection Magnetometryc (PERM) dt ds ds BSurf Apollo 15 & 16 Subsatellites Electron Reflectometry OneHowever, of the the great Apollo surprises 15 & 16 from Subsatellite Apollo was magnetic the discovery data set of paleomagneticis very sparse and fields confined in the lunar within crust 35 degrees. Their existence of the suggestsequator. Attempts that magnetic to correlate fields atsurface the Moon magnetic were muchfields with strongerspecific geologic in the past features than they were are largely today. unsuccessful. Mars Observer (1992-3) – disappeared 3 days before Mars orbit insertion Mars Global Surveyy(or (MGS) 1996-2006 MGS Mag/ER team Current state of knowledge • Very strong crustal fields measured from orbit: – Discovered by MGS: ~10 times stronger than terrestrial fields. – Reqirehgeolmes(>10Require huge volumes (>106 km3) of coherently magneti zed cr ust . – Crustal remnant of a strong dynamo-driven global magnetic field MGS Aerobraking Mars Magnetic Map (from Electron Reflection) What do we Learn about Mars? No significant global field Interior incapable of supporting dynamo today Strong localized magnetic fields Oldest crust magnetized in ancient dynamo Impacts/volcanism erased many sources Variable solar wind field create randomness in map Atmosphere exposed to solar wind in many regions Current state of knowledge • Distribution of crustal fields: – Follows the dichotomy to first-order: strong in South, weak in North. – Shock demagnetization by post-dynamo impacts – Thermal demagnetization by magmatic intrusions (e.g. Tharsis) Current state of knowledge • The Martian dynamo: – Rapid cessation in basin magnetization around 4.1 Gyr ago (H&N). – EittiExcitation mech hianisms: i iitilhtnitial hot core, i nner core f ormati tiion, impact – Termination mechanisms: cooling core, giant impact – Lack of global field → increased atmospheric loss. – Withi n 0 -300 Myr o f cessat ion, c limate h a d lik el y b ecome much d ri er ( end of the Phyllosian era). Martian Climate Evolution Many lines of evidence point to a change in the Martian atmosphere from Earth-like to cold and thin Where did the Atmosphere Go? Up UP Down Pickup Ions Ganymede Aurora in the Solar System Jupiter Observations of Auroral Processes QuickTime™ and a decompressor are needed to see this picture. Brain et al., 2006 Lundin et al., 2006 QuickTime™ and a Bertaux et al., 2005 decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. (Earth) Consequences of Aurora? (Earth) ESAESA MGS Atmospheric Probing Results Atmosp her ic neu tral d ensit y f rom MGS ER measurements, at latitudes of 0-30 S (diamonds), 50-55 S (triangles) and all latitudes (solid line). Dashed lines show aphelion and perihelion. Atmospheric density Solar Energetic Particles Space Weather Effects on Atmosphere • Solar Energetic Particle (SEP) events: – detectable in MGS ER background – deposit energy in atmosphere, heating atmospheric neutrals Protons – enhance atmospheric sputtering –contibttribute t o M ars’ radi ditiation envi ronment Electrons COUP: The Movie (courtesy Feigelson, 2007) Extraordinary flares in analoggygs of the young Sun 1 2 JW 738 K=10.5 ts / ks cc Age ~ 10 Myr log Lp = 32.6 erg/s X-ray Time (13.2 days) Flare 1: Unusual slow-rise morphology. Flare 2: One of the most powerful X-ray flares ever seen 36.8 in any late-type star with Ex ~ 10 erg. Wolk & 7 others 2005 COUP #6 Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars Scout Mission Bruce Jakosky, Principal Investigator University of Colorado Bob Lin, Deputy PI Univ. of California, Berkeley MAVEN Team .