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- 积分
- 17983
- 威望
- 17983
- 包包
- 26159
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The most heavily cratered terrains on Mercury exhibit 6 \/ ~# g1 k: o3 c; H# G# e
a lower density of craters smaller than about 100 km in diameter than on the 4 M& m `7 G. T! G0 O5 @5 C$ u
Moon, a deficit that has been attributed to resurfacing by formation of ancient ( U( B }& A+ }+ q: b8 C
intercrater plains. Simone Marchi et al. used a crater areal density map
" @; O# e M1 y6 H9 H3 vbased on data from the MESSENGER spacecraft (the colour-coded foreground on , [ ? v5 a5 [9 m8 f% e ?
cover, with a global surface mosaic in the background) to locate the oldest
9 n+ u! Z; Q* h% O8 A9 z! _surfaces on Mercury and interpret the crater populations in the framework of a * h8 \2 y/ |8 x! n: N, R1 X! H% `8 r
recent lunar crater chronology. They conclude that the oldest surfaces were
9 s" H3 a* Q- Z4 Lemplaced just after the start of the Late Heavy Bombardment 4.0 to 4.1 billion $ D, Q; f* @0 E1 u) H2 Y
years ago. The large impact basins, not previously dated, yield a similar - }- I% ^- n' b m& T" z* \
surface age. This agreement implies that resurfacing was global and due to - L: l8 Z# [6 A2 b+ f
volcanism, perhaps aided by heavy bombardment as previously suggested. Cover: % x1 N( B+ S. j' N" r
Simone Marchi/MESSENGER data: NASA/JHUAPL/Carnegie Institution of Washington0 i( k/ {4 `$ e! L3 U
2 U* l2 Z4 m! [8 P$ \& j
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发表于 2013-7-5 23:43
发表于 2013-7-6 08:19
