Mercury - Introduction to Planetary Geomorphology - page 101

Figure 5.26. Hilly and lineated ( ) terrain imaged by

Mariner 10 at the antipode to the Caloris impact basin. Crater
rims are broken into massifs, and the intervening terrain consists
of hills and valleys thought to have resulted from focusing of
seismic energy. The smooth plains that fill the 150 km Petrarch
crater (left side) have not been disrupted, indicating their
emplacement after the Caloris impact (NASA Mariner 10
FDS 27370).

“ weird ”

Figure 5.25. An oblique view of Pantheon Fossae, de ned by the set

of troughs that converge near the center of Caloris basin. The
troughs are probably grabens, which would re ect extension of the

smooth plains on the floor of the basin. Ejecta from the 41 km in

diameter impact crater, Apollodorus, is superposed on the troughs
and is dark, suggesting that it has excavated a material different
from that of the smooth plains (NASA PIA 10635).

opposite side) to the Caloris basin. Informally termed
“ weird terrain ” by the science team, and now known as
hilly and lineated terrain, this landscape covers some
250,000 km 2 and consists of various hills and depres-
sions, along with crater rims that have been broken into
large blocks ( Fig. 5.26 ). Pete Schultz and Don Gault
( 1975 ) estimated the energy that was generated from
the Caloris impact and noted that seismic surface and
body waves would travel around and through Mercury to
focus at the antipode ( Fig. 5.3 ). In this region, the crust
would have been highly disrupted, with the surface lifted
tens of meters vertically, breaking up the crust and lead-
ing to the jostled appearance of the terrain.
The Rembrandt basin was discovered during the
second flyby of Mercury by MESSENGER ( Fig. 5.27 ).
As documented by Smithsonian planetary geologist
Tom Waters and his MESSENGER science team col-
leagues (Waters et al., 2009 ), this 715 km in diameter
impact structure is about the same age as the Caloris
basin but shows distinctive features indicative of a
complex tectonic history. As with Caloris, the main
ring is identi ed by an inward-facing scarp and massifs
that are more than 1 km high. Hummocky and radially
textured ejecta are seen beyond the ring, especially to

Figure 5.27. AmosaicofMESSENGER images for
Rembrandt basin, a 715 km impact structure
comparable in age to the Caloris basin. Note the lobate
scarp (arrow) that cuts across the basin (NASA MESSENGER
mosaic).