Analysis of MESSENGER Gamma-Ray Spectrometer data from the Mercury flybys

摘要: Abstract During its three flybys of Mercury, the MESSENGER spacecraft made first detection gamma-ray emission from planet's surface. With a closest approach distance ∼200 km, provided an opportunity to measure elemental abundances Mercury's near-equatorial regions, which will not be visited at low altitude during MESSENGER's orbital mission phase. Despite being limited by planetary photon flux, sufficient counts were accumulated two estimate bounds on for some elements having relatively strong spectral peaks, including Si, Fe, Ti, K, and Th. Only Si is standard deviation σ sufficiently small conclude that this element was detected with 99% confidence. Iron potassium are 2− (95% confidence) level, whereas only upper Ti Th can determined. Relative abundance assumed 18 weight percent (wt%), have been estimated as 9.7 wt% 7.0 wt% 0.087 wt% 2.2 ppm The bound K rules out previously suggested models surface composition regions sampled. Upper Fe/Si Ti/Si ratios generally consistent Fe analysis measurements Neutron Spectrometer but also permissive much lower concentrations.