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The most heavily cratered terrains on Mercury exhibit
; Z5 x) h8 y' f% G9 M# Q3 {a lower density of craters smaller than about 100 km in diameter than on the ( j0 h, h) T/ c- G7 ]9 s
Moon, a deficit that has been attributed to resurfacing by formation of ancient
8 r9 e# R' G! O/ Rintercrater plains. Simone Marchi et al. used a crater areal density map ! M. V% A" S4 ]8 _: |4 d+ o* l5 f; H0 s( O
based on data from the MESSENGER spacecraft (the colour-coded foreground on
" z' a- C: K8 r3 x1 q1 Lcover, with a global surface mosaic in the background) to locate the oldest ( l# p3 G+ {5 A* @+ H1 g3 u
surfaces on Mercury and interpret the crater populations in the framework of a
! s% ^- c6 R2 }: p* Lrecent lunar crater chronology. They conclude that the oldest surfaces were $ g7 W8 s4 v' N, r, F$ ^9 Y. d* T
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
* X& i; }7 F% a9 _, wyears ago. The large impact basins, not previously dated, yield a similar , S% x8 ~. p! {8 V
surface age. This agreement implies that resurfacing was global and due to
2 n' M% p6 m! ^$ z0 s avolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: ; @& d, L$ S1 R& m" 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
