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The most heavily cratered terrains on Mercury exhibit # w" z) M- F* L) L) i- H& r1 @
a lower density of craters smaller than about 100 km in diameter than on the " P- ~9 E5 d. g$ S8 \! b! s
Moon, a deficit that has been attributed to resurfacing by formation of ancient # h( ?7 x, W2 h X2 X4 Q0 m: {7 R% L
intercrater plains. Simone Marchi et al. used a crater areal density map ) P- a+ D Q" H5 i& `
based on data from the MESSENGER spacecraft (the colour-coded foreground on ; O' m, J/ x* q% t, q4 m
cover, with a global surface mosaic in the background) to locate the oldest 7 g( n5 p$ E' H- q' ]! ?
surfaces on Mercury and interpret the crater populations in the framework of a
$ N" D7 o. A- W2 g5 }& ^2 A% mrecent lunar crater chronology. They conclude that the oldest surfaces were % C0 i( v# U7 d7 L2 [
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion
: o- F& A1 z( s& f$ fyears ago. The large impact basins, not previously dated, yield a similar ) J) c2 a) {* k4 k; N/ }
surface age. This agreement implies that resurfacing was global and due to
' F& R6 w5 i z3 M2 S5 rvolcanism, perhaps aided by heavy bombardment as previously suggested. Cover: / x2 [- y5 b1 A" P
Simone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington9 C3 E0 n$ J/ |5 X: L. h% S
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发表于 2013-7-5 23:43
