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1 ?% }7 z; D4 ^; x+ j5 S3 MThe most heavily cratered terrains on Mercury exhibit
3 w, A# G! [4 @/ } C# \ ^' ta lower density of craters smaller than about 100 km in diameter than on the
$ p5 m; }) {. D: K$ [Moon, a deficit that has been attributed to resurfacing by formation of ancient 6 d' q+ _. Q) Z% ~# A, Q
intercrater plains. Simone Marchi et al. used a crater areal density map 4 G7 W3 e4 y3 J
based on data from the MESSENGER spacecraft (the colour-coded foreground on # c- i6 x' [: M, b: I/ B7 i
cover, with a global surface mosaic in the background) to locate the oldest
) m- U) \5 _* k0 N/ m# |surfaces on Mercury and interpret the crater populations in the framework of a - N5 O6 `" c+ V: d9 v1 {6 w3 {+ H
recent lunar crater chronology. They conclude that the oldest surfaces were 7 x$ N+ S7 x: p
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
6 O" k& k2 c Dyears ago. The large impact basins, not previously dated, yield a similar
7 K/ x3 |$ {& t) {7 X ?! o( Csurface age. This agreement implies that resurfacing was global and due to x" `% W) j& m" @
volcanism, perhaps aided by heavy bombardment as previously suggested. Cover: 1 {$ n# m* P/ H6 b a& {
Simone 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
