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- 26159
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, I2 e/ s& ]0 P( k6 _2 s0 kThe most heavily cratered terrains on Mercury exhibit
6 T, ?) V6 m; J6 Ya lower density of craters smaller than about 100 km in diameter than on the
/ M0 V# @( s+ ?2 P2 z/ R- P+ `Moon, a deficit that has been attributed to resurfacing by formation of ancient 2 d# J5 s4 i- N9 m: c9 S
intercrater plains. Simone Marchi et al. used a crater areal density map 9 F1 s- {( i" a, B' h7 t- e
based on data from the MESSENGER spacecraft (the colour-coded foreground on 4 }- b) F/ U. ~& E
cover, with a global surface mosaic in the background) to locate the oldest - t. U# ?/ S# ^3 o# `. _/ t
surfaces on Mercury and interpret the crater populations in the framework of a 8 t2 M- M S, y, K: a: S# O
recent lunar crater chronology. They conclude that the oldest surfaces were ) z0 |+ o2 k8 ^2 O+ b
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion : c5 G( E# `% P4 C1 l$ `
years ago. The large impact basins, not previously dated, yield a similar
# h" H/ \* L* ^3 `; xsurface age. This agreement implies that resurfacing was global and due to
5 f0 L6 R/ M" _) M& ]+ hvolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: + X1 x1 f0 J! ?
Simone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington
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发表于 2013-7-5 23:43
