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The most heavily cratered terrains on Mercury exhibit . V: w% k8 N J4 d0 A# V
a lower density of craters smaller than about 100 km in diameter than on the
, r1 P& b+ l; n% u3 S: y0 V; }Moon, a deficit that has been attributed to resurfacing by formation of ancient 7 G# Y. Z2 t8 V# z7 q7 q: F2 e$ k( }
intercrater plains. Simone Marchi et al. used a crater areal density map
. p0 U* B- f* N& a( Vbased on data from the MESSENGER spacecraft (the colour-coded foreground on " O: O' f8 V8 j T) `8 `3 e
cover, with a global surface mosaic in the background) to locate the oldest & f6 N- V$ [# Y5 T
surfaces on Mercury and interpret the crater populations in the framework of a ) c5 {+ ~4 [& K& I' P) |- }
recent lunar crater chronology. They conclude that the oldest surfaces were
( F6 |8 t- S- V+ Jemplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion % @) C1 E2 N' q, b; i# |5 X
years ago. The large impact basins, not previously dated, yield a similar
8 S4 W. Z6 ]5 x* Ssurface age. This agreement implies that resurfacing was global and due to
/ ?+ o4 F8 ?3 Uvolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: 0 X. s# @7 B9 O% T, }
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
