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- 26159
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/ g7 j& B' h1 e7 Z+ }# h. EThe most heavily cratered terrains on Mercury exhibit # Q9 S" O4 S, M# B
a lower density of craters smaller than about 100 km in diameter than on the # K6 M: U6 A8 ?: U* s2 }
Moon, a deficit that has been attributed to resurfacing by formation of ancient ( T3 P, d. ^& C6 j: {1 E& b& g& u
intercrater plains. Simone Marchi et al. used a crater areal density map * k' D M( h* p9 A" V
based on data from the MESSENGER spacecraft (the colour-coded foreground on , r9 Y/ j! l# L+ E) h
cover, with a global surface mosaic in the background) to locate the oldest
$ k' D/ [* l! gsurfaces on Mercury and interpret the crater populations in the framework of a
T: v5 [% k Q, erecent lunar crater chronology. They conclude that the oldest surfaces were
v0 G8 j5 a+ p" \7 [1 t- K7 l' R: Demplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion 3 X$ m" G% o' G% B8 U( X
years ago. The large impact basins, not previously dated, yield a similar
/ C2 _1 H" q9 H2 K v7 v; w3 }$ Esurface age. This agreement implies that resurfacing was global and due to
* [' u1 J4 T' s; Fvolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: " W+ R+ i9 i) ?8 X Z$ {! x: L
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
