Fine-Grained Rocks at Hogwallow Flats

Perseverance’s exploration of the Hawksbill Gap area of the Jezero Delta continues! The rover has abraded at two different locations over the last few weeks. First, the rover abraded in the Devil’s Tanyard area. Unfortunately, the crumbly rocks at Devils Tanyard were broken and moved by the force of the abrasion. Nevertheless, the team was able to use the SuperCam and Mastcam-Z instruments to gather valuable scientific data of the abrasion patch and surrounding area.

The rover then made its way up the delta to abrade at Hogwallow Flats, an area nicknamed “the Bacon Strip” by the team due to its light-colored striped rocks, which look like a strip of bacon in images taken by the Hi-Rise orbiter. The rocks at Hogwallow Flats appear to be very fine-grained, which is exciting to scientists on the mission as fine-grained rocks may have the best chance at preserving evidence of life. In order to understand why, we need to talk a little about organic molecules.

Molecules made up of mostly carbon, hydrogen, and oxygen are called organic molecules and are the primary building blocks of life on Earth. Some small organic molecules can be produced without the presence of life (and have been detected on Mars and in meteorites in the past), so the presence of organic molecules in a rock does not automatically mean that life was present. However, the detection of particularly large and complex organic molecules, or specific patterns of organic molecules, could be considered a biosignature. Unfortunately, large and complex molecules break down into smaller ones over time due to radiation from the sun and reactions with the rocks and atmosphere. If there was life in Jezero crater 3-4 billion years ago, most of the large organic molecules created by it would have been destroyed, leaving little evidence of the presence of life.

In order to have a chance of detecting evidence of life in the samples that Perseverance will ultimately send back, we need to sample rocks that have the best chance of preserving complex organic molecules – fine-grained rocks. This is because fine-grained rocks are more likely to contain large amounts of clay minerals than rocks with lots of sand, pebbles, and gravel. Clay minerals have charged surfaces that can bind to organic molecules, kind of like how magnets with opposite charges stick together. By being attached to clay minerals in this way, complex organic molecules can be protected from damage in the harsh Martian environment, and preserved over a much longer period of time then they would be otherwise.

The team plans for Perseverance to explore several more sites on the delta front before deciding where it will sample. We will continue to keep an eye out for more fine-grained rocks as we continue on from Hogwallow!

Written by Lydia Kivrak, Student Collaborator at University of Florida