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The most heavily cratered terrains on Mercury exhibit
8 g9 Z. r$ `6 I- Na lower density of craters smaller than about 100 km in diameter than on the % O* y1 E- |) G0 ]+ }: C
Moon, a deficit that has been attributed to resurfacing by formation of ancient
! O. k& L: b& z+ _2 N* dintercrater plains. Simone Marchi et al. used a crater areal density map & R8 R0 c8 c! O
based on data from the MESSENGER spacecraft (the colour-coded foreground on ( L" h2 s, a! Z
cover, with a global surface mosaic in the background) to locate the oldest
) y+ o4 y, O! @. Y2 vsurfaces on Mercury and interpret the crater populations in the framework of a & `4 L- B1 {/ y$ \+ I( A" [
recent lunar crater chronology. They conclude that the oldest surfaces were
" ^5 a' A* `! ?0 Z4 t5 Aemplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
" P3 N5 T! j( O$ N4 w3 F) w- P- uyears ago. The large impact basins, not previously dated, yield a similar
. W6 d# y9 i3 q: X/ _& u7 ?surface age. This agreement implies that resurfacing was global and due to
% g# K6 W: _: w6 Zvolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: % e2 E& c( R' x3 G( P
Simone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington' Y6 E8 ^# T. S+ q
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发表于 2013-7-5 23:43
