Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u11c..01s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U11C-01
Other
5405 Atmospheres (0343, 1060), 5430 Interiors (8147), 5440 Magnetic Fields And Magnetism, 5443 Magnetospheres (2756), 5470 Surface Materials And Properties
Scientific paper
MESSENGER 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 2008 and will do so again on 6 October 2008. Objectives of the flybys include 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, detected two outbound current-sheet boundaries that may indicate a planetary ion boundary layer, but did not observe energetic magnetospheric electrons as reported by Mariner 10. 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 will reveal more than 30% of the planet never before seen at close range, improve knowledge of Mercury's low-degree gravity field and its implications for the structure of the planet's core, and feature targeted observations of the surface, exosphere, and tail that have profited from the experiences of the first flyby.
Anderson Benjamin J.
Domingue Donovan L.
Evans Larry G.
Gold Robert E.
Head James W.
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