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Speaker: Dr. Sean C. Solomon, Dept of Terrestrial Magnetism, Carnegie Institution of Washington (D.C.)
Time and Location: Talk starts at 1:00 pm with Q&A to follow. It will be held in one of the first floor conference rooms at the American Center for Physics, One Physics Ellipse, College Park, MD. This is located off River Road, between Kenilworth Ave. and Paint Branch Parkway.
Abstract: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, developed under NASA’s Discovery Program, is the first spacecraft to visit the planet Mercury in more than 30 years. En route to insertion into orbit about Mercury in March 2011, MESSENGER flew by the innermost planet on 14 January and 6 October 2008. Objectives of the flybys included color imaging of the surface, the first high-resolution spectral reflectance measurements (from ultraviolet to near-infrared wavelengths) of surface composition, the first spacecraft altimetric measurements of surface topography, the first measurements of the abundances and compositions of plasma ions in Mercury’s magnetosphere, the deepest penetrations yet into Mercury’s magnetosphere, and searches for previously undetected species in Mercury’s surface-based exosphere and neutral sodium tail. MESSENGER’s first flyby confirmed that Mercury’s internal magnetic field is primarily dipolar, documented water-group and other ions in the magnetosphere, mapped a north-south asymmetry in the Na tail and determined the Na/Ca ratio near the tail and near the dawn terminator, and detected two outbound current-sheet boundaries that may indicate a planetary ion boundary layer. The laser altimeter demonstrated that the equatorial topographic relief of Mercury is at least 5 km. MESSENGER’s images provided evidence for widespread volcanism, and candidate sites for volcanic centers were identified. Also revealed were newly imaged lobate scarps and other tectonic landforms supportive of the hypothesis that Mercury contracted globally in response to interior cooling and growth of a solid inner core. Reflectance spectra show no evidence for FeO in surface silicates, and MESSENGER’s neutron spectrometer yielded an upper bound of 6% on the surface Fe abundance. The reflectance and color imaging observations support earlier inferences that Mercury’s surface material consists dominantly of iron-poor, calcium-magnesium silicates with an admixture of spectrally neutral opaque minerals. The October encounter revealed another 30% of the planet never before seen at close range, improved knowledge of Mercury’s low-degree gravity field and its implications for the structure of the planet’s core, and featured targeted observations of the surface, exosphere, and tail.
Biography: Sean C. Solomon is Director of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. Educated at Caltech (B.S., 1966) and MIT (Ph.D., 1971), he was a member of the MIT faculty for more than 20 years. A seismologist, marine geophysicist, and planetary scientist, Solomon has worked on a wide range of problems in earthquake seismology, geodynamics, magmatism, and the geological and geophysical evolution of the terrestrial planets. He served on science teams for the Magellan and Mars Global Surveyor missions, and he is the Principal Investigator for the MESSENGER mission to Mercury. Solomon is a member of the National Academy of Sciences, a Fellow of the American Academy of Arts and Sciences, and a past President of the American Geophysical Union. He received the Arthur L. Day Prize from the National Academy of Sciences, the G. K. Gilbert Award from the Geological Society of America, the Harry H. Hess Medal from the American Geophysical Union, and the NASA Public Service Medal.