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/ J5 b" Q V2 m; X/ t3 kThe most heavily cratered terrains on Mercury exhibit 9 x q" \' m' L* r
a lower density of craters smaller than about 100 km in diameter than on the 4 o$ G& F" E1 x
Moon, a deficit that has been attributed to resurfacing by formation of ancient 6 Z" V2 ^. n' x0 T- h
intercrater plains. Simone Marchi et al. used a crater areal density map
, T1 z4 i3 x# p* V# s3 A4 B: gbased on data from the MESSENGER spacecraft (the colour-coded foreground on
6 i/ J1 h$ `# o; mcover, with a global surface mosaic in the background) to locate the oldest
9 x$ W+ |+ i$ ?, C2 Z4 q5 ~, Q6 \& [! rsurfaces on Mercury and interpret the crater populations in the framework of a
8 j e. y" o# {5 q# v: I9 trecent lunar crater chronology. They conclude that the oldest surfaces were . w( n. F5 F2 R$ m
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
, F6 S( \1 e6 B8 nyears ago. The large impact basins, not previously dated, yield a similar
$ x& Q3 T2 ]" m" q, S- a9 usurface age. This agreement implies that resurfacing was global and due to
% d) _# e% ~" a% w% u! f$ Evolcanism, perhaps aided by heavy bombardment as previously suggested. Cover:
' T1 h2 w4 z0 v! N; oSimone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington* [5 T) z1 {) F
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发表于 2013-7-5 23:43
