Martian Features Provoke Sharp Debate

Photo courtesy of NASA/JPL/Cornell Razorbacks photographed by NASA’s Mars rover Opportunity

Geological features on Mars, including some strange sharp features called razorbacks, have been suggested as evidence of liquid water. However, granular materials researcher Troy Shinbrot of Rutgers University has found that these features could be produced by dry dust grains rather than flowing water. He reported his results at the March Meeting.

The pointy razorbacks, a few centimeters high and less than a centimeter wide, photographed by NASA’s Mars rovers, have intrigued observers. Some scientists believe they may have been produced recently by flowing water. Other stream-like features on Mars have also been cited as evidence of water.

Shinbrot wondered whether these features could be associated with completely dry grains rather than flowing water. He created a simple setup to find out. He placed a pile of light, hollow glass beads in a box and tilted it. As the box is tipped, the light grains create a mini dust storm and eventually settle down. Shinbrot found that he could make the glass grains fall in patterns resembling many features seen on Mars, from wide apron-like features to thin sinuous streams.  

Though the patterns in the lab experiment are on a much smaller scale than those on Mars, Shinbrot believes they are comparable because the grains settle slowly compared with the speed at which they flow downhill, as dust grains would in Mars’ low gravity.

Sharp features resembling the razorbacks seen on Mars could also be produced in a similar setup in the lab by applying an electric field to the grains, Shinbrot found. When the box was tilted, some of the tiny grains clumped together as they became airborne, and landed in the spiky formations similar to Martian razorbacks. Electric fields could build up on Martian sand grains as they slide past each other because Mars is so dry, he reported. “These features that look like water may simply be dry features,” said Shinbrot.