Lava, not water, may have carved the biggest channels on Mars.
Ever since NASA's Mariner 9 spacecraft beamed back the first
images of the channels in the 1970s, most people have assumed
they were created by massive floods. But David Leverington of
Texas Tech University in Lubbock says flowing water would have
left behind much more sediment than is seen. There are also few
minerals that form in liquid water present. Lava, however, is
known to have carved big channels on the moon. And Leverington
points out that some of the channels on Mars start on the flanks
of volcanoes and end in large deposits of solidified lava
(Geomorphology, DOI: 10.1016/j.geomorph.2011.05.022). Kelin
Whipple of Arizona State University (ASU) in Tempe agrees that
lava probably carved the huge channels, such as Kasei Valles
(shown). He says the study calls into question the case for huge
volumes of water – and possibly an ocean – on ancient Mars. But
Phil Christensen, also at ASU, says clays and fans of sediment
still point to the existe