Searching for Concentrated Biosignatures in an Ancient, Martian Mud Lake

Category: Press Release

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October 18, 2023, Tucson, Arizona – A landmark discovery by a collaborative team led by
the Planetary Science Institute’s Alexis Rodriguez has unveiled evidence of sedimentary
plains created by aquifer drainage within Martian collapse formations termed chaotic
terrains.

“Our research focuses on a sedimentary unit within Hydraotes Chaos, which we interpret to
be the remnants of a mud lake formed by discharges from gas-charged mudstone
stratigraphy dating back to nearly 4 billion years ago, a time when the surface of Mars was
likely habitable. These sediments might harbor evidence of life from that or subsequent
periods. It is important to remember that the subsurface of Mars might have included
habitability lasting the duration of life’s history on Earth,” said Rodriguez, lead author of
the paper “Exploring the evidence of middle Amazonian aquifer sedimentary outburst
residues in a Martian chaotic terrain” that appears in Nature Scientific Reports.

PSI scientists Bryan Travis, Jeffrey S. Kargel and Daniel C. Berman are co-authors on the
paper. Scientists from NASA Ames Research Center, the University of Arizona, Autonomous
University of Barcelona, Blue Marble Space Institute of Science, and the University of
Florida are also co-authors on the project.

The extensive study of Martian aquifer drainage has revealed enormous flood channels that
stretch thousands of kilometers into the planet’s northern lowlands. The prodigious
erosion caused by these channels, combined with the subsurface sediments released from
the aquifers, blankets extensive portions of the northern lowlands. This complex landscape
presents a formidable challenge for the investigation of the nature of the Martian aquifers.

“Venturing into the northern plains for sampling could prove precarious, as distinguishing
between materials sourced from the aquifers and those eroded and transported during
channel formation could become an intricate task. The plains, situated within Hydraotes
Chaos, offer a unique glimpse into ancient aquifer materials. These plains, which we think
formed from mud extruding into a basin directly above their source aquifer, provide a more
targeted exploration opportunity,” Rodriguez said. “Unlike vast flood channels with their
complex erosion patterns, this finding simplifies the examination of Martian aquifers,
reducing the risk of overland sedimentary acquisition, and opens a new window into Mars’
geological past.”

“Our numerical models reveal a fascinating story. The lake’s source aquifer likely
originated from phase segregation within the mudstone, forming vast water-filled
chambers, several kilometers wide and hundreds of meters deep. This process was likely
triggered by intrusive igneous activity. Moreover, the observed segmented subsidence
across the chaotic terrain suggests an interconnected network of chambers, depicting
stable water-filled giant caverns, some reaching kilometers in widths and lengths, way
larger than any known Earth counterparts,” co-author Travis said.

“Initially biomolecules could have been dispersed throughout the volume of large
groundwater filled cavities. As the water was released to the surface and ponded, the water
went away leaving behind lags of sediments and potentially high concentrations of
biomolecules.” Rodriguez said.

Therefore, the residue of this ancient mud lake could provide unprecedented access to
aquifer materials enriched in biomolecules that have remained hidden within Mars’
subsurface for most of its existence.

“NASA Ames is considering the plains as a possible landing site for a mission to search for
evidence of biomarkers, specifically lipids. These biomolecules are extremely resistant and
could have endured billions of years on Mars,” co-author Mary Beth Wilhelm of NASA Ames
Research Center said.

“In addition, the study region includes widespread mud volcanoes and possible diapirs,
providing additional windows into subsurface, potentially habitable rocks. A small rover
could within short distances sample the mud lake sediments and these materials,
dramatically increasing the odds of biosignature detection,” co-author Kargel said.

“Our crater counts indicate that the plains are relatively recent, returning an age of 1 billion
years. This age is good news for our search for life. This age is way younger than the ages of
most aquifer releases on Mars, dating back to approximately 3.4 billion years ago. So, the
materials spent a huge amount of time in the subsurface.” co-author Berman said.

Funding for the project was from a grant to PSI from Mars Data Analysis Program (MDAP)
grant number 80NSSC19K1490 and a 2020 NASA Ames research innovation award.

Above, view of Hydraotes Chaos (white outline), including the location of the proposed mud lake (black arrow). Below, lobate margin forming part of a constant elevation contact, which we interpret as the lake’s inundation periphery. We plan to land somewhere near here. Credit: NASA.

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