When the Mars Exploration Rover Spirit reached the top of Husband Hill in the Columbia Hills of Gusev Crater on August 22, 2005, it stood 107 meters (351 feet) above its landing site. Yet if recent work is right, the hill Spirit climbed was much lower and smaller than it was originally.
THE HILLS OF OLD. Today's Husband Hill in Gusev Crater is a smaller feature than it was in ancient times, when sedimentary layers draped across it. Details in the orientation and tilt of those layers led to a reconstruction of an ancient Husband Hill perhaps twice as high as it is currently. (Image taken from the poster paper.)
At the 2012 fall meeting of the American Geophysical Union, a team of scientists led by Shoshanna Cole (Cornell University) presented a poster paper with evidence for a significantly larger and higher Husband Hill in ages past.
Mars scientists have tentatively dated the Columbia Hills as Late Noachian to Late Hesperian (roughly 3.1 to 3.8 billion years ago). The Hills are likely the remnants of either Gusev’s central peak or overlapping rims from impact craters that formed within Gusev.
The team studied more than 7,000 Pancam and Navcam images from Spirit’s traverse of West Spur and Husband Hill. For each outcrop that showed layers, they measured the angle of the bedding planes and their direction of tilt (dip and strike, respectively), plotting these onto a HiRISE photomap of Husband Hill with contour lines giving elevations.
The team observed that the exposed outcrops show strikes and dips that fit what would be seen in layers draping across an older structure. But the dips were steeper than the slope of the ground surface at the outcrop. This led the team to conclude that the ancient Columbia Hills were larger and higher than the present-day ones.
How much higher? Hard to say, but the projected summit elevation could be twice the current one, or about 200 meters (700 ft).
Mapping the orientations of outcrops with similar compositions also showed another facet of the earlier Hills: their highest point lay to the northwest of the current summit (Husband Hill). It was above what is the modern Tennessee Valley and away from the central axis of today’s Columbia Hills.