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The most heavily cratered terrains on Mercury exhibit 9 c/ u5 e8 F0 K
a lower density of craters smaller than about 100 km in diameter than on the
2 m% Y7 L2 l' e# [) A+ X: SMoon, a deficit that has been attributed to resurfacing by formation of ancient
- ]0 R4 c# A. U$ vintercrater plains. Simone Marchi et al. used a crater areal density map . A2 [( u2 @, z1 d$ D! b
based on data from the MESSENGER spacecraft (the colour-coded foreground on 7 k' r- H8 d% B+ o7 ?# M& S4 P
cover, with a global surface mosaic in the background) to locate the oldest
Y% f# n( G0 X4 g, Esurfaces on Mercury and interpret the crater populations in the framework of a , y) g8 v6 `: V( k& }
recent lunar crater chronology. They conclude that the oldest surfaces were 5 T/ }6 m0 ?- Q' S2 g* {
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
) \# ?9 P! P! h& X8 I* K% Gyears ago. The large impact basins, not previously dated, yield a similar
. n. v7 O) V. rsurface age. This agreement implies that resurfacing was global and due to
( u0 p) R: L' l4 j$ u" \7 X/ x5 svolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: & P4 G' E. H, w& B! i! a m
Simone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington
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发表于 2013-7-5 23:43
