Concentrically-Fractured Depression on Mars Could Be Place to Look for Signs of Microbial Life

An unusual depression in the northern Hellas basin on Mars could be a new place to look for life on the planet, says a team of planetary researchers. The depression was probably formed by a volcano beneath a glacier and could have been a warm environment well suited for microbial life.

The Hellas depression. Left: regional view; arrows denote channel locations that cross-cut both the crater fill and the concentric fracture system. Right: close-up view of the depression. Image credit: Joseph S. Levy et al.

“We were drawn to this site because it looked like it could host some of the key ingredients for habitability — water, heat and nutrients,” said Dr. Joseph Levy, a researcher at the University of Texas Institute for Geophysics and lead author of a paper published this month in the journal Icarus.

The depression is inside a crater perched on the rim of the Hellas basin and surrounded by ancient glacial deposits.

Another depression in the Galaxias Fossae region of Mars had a similar appearance.

“These landforms caught our eye because they’re weird looking,” Dr. Levy said.

“They’re concentrically fractured so they look like a bulls-eye. That can be a very diagnostic pattern you see in Earth materials.”

Dr. Levy and co-authors used pairs of high-resolution images to create digital elevation models of the depressions that enabled in-depth analysis of their shape and structure in 3D.

The analysis revealed that both Hellas and Galaxias depressions shared an unusual funnel shape, with a broad perimeter that gradually narrowed with depth.

“That surprised us and led to a lot of thinking about whether it meant there was melting concentrated in the center that removed ice and allowed stuff to pour in from the sides,” Dr. Levy said.

“Or if you had an impact crater, did you start with a much smaller crater in the past, and by sublimating away ice, you’ve expanded the apparent size of the crater.”

The Galaxias depression. Left: regional view. Right: close-up view of the depression. Image credit: Joseph S. Levy et al.

After testing formation scenarios for the two depressions, the team found that they probably formed in different ways.

“The debris spread around the Galaxias depression suggests that it was the result of an impact — but the known volcanic history of the area still doesn’t rule out volcanic origins,” Dr. Levy said.

“In contrast, the Hellas depression has many signs of volcanic origins. It lacks the surrounding debris of an impact and has a fracture pattern associated with concentrated removal of ice by melting or sublimation.”

“The interaction of lava and ice to form a depression would be an exciting find because it could create an environment with liquid water and chemical nutrients, both ingredients required for life on Earth,” he said.

“The Hellas depression and, to a lesser extent, the Galaxias depression, should be kept in mind when looking for habitats on Mars.”

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Joseph S. Levy et al. Candidate volcanic and impact-induced ice depressions on Mars. Icarus, published online November 2, 2016; doi: 10.1016/j.icarus.2016.10.021