Geoscience Reference
In-Depth Information
(a)
(b)
10
-1
Lunar
highlands
10
-1
Mercury
highlands
Class-1
10
-2
10
-2
10
100
1000
10
100
1000
R
10
0
(c)
(d)
Lunar highlan
d
s
10
-2
Mars
northern plains
10
-1
10
-4
Venus
Mars
highlands
10
-6
10
-8
10
-2
Ea
rt
h
Mars
northern
plains
10
-10
10
-12
1
10
100
1000
0.01
0.1
1
10
100
1000
D
[km]
Fig. 1.
R
-plots of some crater SFDs. (a) Lunar highlands craters and lunar Class-1
craters. (b) Craters on the oldest mercurian highlands. (c) Craters on the oldest mar-
tian highlands and on young northern plains. (d) Craters on Venus and on the Earth,
compared with the lunar highlands craters and young martian craters.
have flat
R
curves with lower density than the old highland craters (lower
left part of Fig. 1(a)). The crater records on Venus and the Earth have
been severely obliterated and lost, or many of their projectiles have been
screened out by the atmosphere, and we cannot use them to estimate their
projectile sources (Fig. 1(d)).
The similarities amongst the wavy
R
curves of the oldest crater popula-
tions on the Moon, Mercury, and Mars indicate that they were created by
a single projectile population at the same age, probably during LHB with a
short timescale. On the other hand, the younger crater populations charac-
terized by the flat
R
curves having a variety of ages have presumably been
created by a different projectile population with a different mechanism.
