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- 积分
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The most heavily cratered terrains on Mercury exhibit * A- O0 ~) j# \: B# E v
a lower density of craters smaller than about 100 km in diameter than on the
. Y+ O; L' M1 f5 e% c+ b; \) s. z# \Moon, a deficit that has been attributed to resurfacing by formation of ancient # }% q# r! y6 o {
intercrater plains. Simone Marchi et al. used a crater areal density map
2 H6 Y, J; g, R9 x* \based on data from the MESSENGER spacecraft (the colour-coded foreground on
* i8 Y# L% O& T+ D/ H1 J+ p& Vcover, with a global surface mosaic in the background) to locate the oldest
+ W3 l" U* U( d2 `0 vsurfaces on Mercury and interpret the crater populations in the framework of a 1 c: M& p5 C ^9 K2 T
recent lunar crater chronology. They conclude that the oldest surfaces were
. p; ~/ m( S; Zemplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion ! h: l& x* f( F0 \/ D( A# `8 l z' B
years ago. The large impact basins, not previously dated, yield a similar 6 ~6 l5 f' o2 v3 a/ }. y
surface age. This agreement implies that resurfacing was global and due to # z' Y4 l4 T1 A2 Y: d4 d. R4 _5 r
volcanism, perhaps aided by heavy bombardment as previously suggested. Cover:
5 j6 A- | V7 @1 C' W" D$ wSimone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington2 V2 @; r# ~6 K. \% U
4 i8 }6 ^5 Z; Q& }3 ]
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发表于 2013-7-5 23:43
发表于 2013-7-6 08:19
