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+ P( L: }2 m( o- `, _3 m: W0 RThe most heavily cratered terrains on Mercury exhibit
* _8 ~. t1 ~8 Y! R; e4 @( Ca lower density of craters smaller than about 100 km in diameter than on the
2 G1 n3 j5 x9 F' Q8 WMoon, a deficit that has been attributed to resurfacing by formation of ancient
* D" g4 F- }8 d8 W. Rintercrater plains. Simone Marchi et al. used a crater areal density map
8 @: A" f0 i4 F7 Sbased on data from the MESSENGER spacecraft (the colour-coded foreground on
+ y/ m9 h9 C1 v* u% vcover, with a global surface mosaic in the background) to locate the oldest
r, b+ ~! o7 T, g) h1 C9 usurfaces on Mercury and interpret the crater populations in the framework of a * @( ], C' h% ^% t! k8 v; X% q
recent lunar crater chronology. They conclude that the oldest surfaces were # H) b2 _- @$ s- F: [! `. ]
emplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion P$ s) s& Q1 P, t, Z" n
years ago. The large impact basins, not previously dated, yield a similar 7 K9 ?1 }& V( J
surface age. This agreement implies that resurfacing was global and due to - R2 m% J- B8 V0 K
volcanism, perhaps aided by heavy bombardment as previously suggested. Cover:
$ G) u1 T' \9 t. sSimone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington# k6 \3 }& z! G6 s( Z: b2 d; E
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发表于 2013-7-5 23:43
发表于 2013-7-6 08:19
