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1 ?. c7 l: o2 n) G4 u% j- uThe most heavily cratered terrains on Mercury exhibit " E, n' i: x& x) D. S) {
a lower density of craters smaller than about 100 km in diameter than on the . ? D4 r- D5 n' v
Moon, a deficit that has been attributed to resurfacing by formation of ancient 4 w4 p) W; {; o$ V( z/ \
intercrater plains. Simone Marchi et al. used a crater areal density map ! V1 l! }6 C$ T5 ^
based on data from the MESSENGER spacecraft (the colour-coded foreground on
3 s! n% R) T. k4 o8 N3 qcover, with a global surface mosaic in the background) to locate the oldest
- Y& x8 P2 S. v& rsurfaces on Mercury and interpret the crater populations in the framework of a 5 E3 C H3 S* z
recent lunar crater chronology. They conclude that the oldest surfaces were * ]( d5 [; t1 I; Z3 r
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
7 w2 }: S" v$ vyears ago. The large impact basins, not previously dated, yield a similar
2 d8 E" k1 R7 V; I% J$ p* _5 C( tsurface age. This agreement implies that resurfacing was global and due to 6 m2 y# y5 W! G9 N) ]
volcanism, perhaps aided by heavy bombardment as previously suggested. Cover:
/ z5 h) x6 P& M5 X% GSimone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington
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发表于 2013-7-5 23:43
发表于 2013-7-6 08:19
