Decoding the Ancient History of a Martian Lake: NASA's Perseverance Rover Sheds Light

The date is December 12, 2023

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The NASA's Perseverance rover celebrated its thousandth day on Mars. It has just finished exploring a historical river delta, which holds evidence of a lake that filled up the Jezero Crater billions of years ago. Until now, the six-wheeled robotic scientist has accumulated 23 samples that shed light on this region of Mars' geological history.

Out of the samples collected, 'Lefroy Bay' boasts a considerable amount of fine-grained silica, which, on Earth, is known to preserve ancient fossils of life. While 'Otis Peak' contains a significant amount of phosphate, a substance often associated with life as we know it. Both the samples are also abundant in carbonate, which helps to record the environmental conditions from the time the rock was originally formed.

The findings were presented at the American Geophysical Union fall meeting in San Francisco on Tuesday, Dec. 12.

Perseverance's project scientist, Ken Farley of Caltech explained, 'We selected Jezero Crater as the landing site as it showed clear evidence of a previous delta, indicating that once a large lake had filled the crater. Given that the delta rocks are an excellent environment for encapsulating indicators of ancient life as fossils, these results have helped to chart the crater's geological history, tracing its phase of the lake and river from the start to the end.'

Jezero was formed due to an asteroid impact around 4 billion years back. Perseverance, which landed in February 2021, found that the crater floor is made of igneous rock that was either formed from magma underground or due to surface volcanic activities. They also discovered sandstone and mudstone, indicating the arrival of the first river in the crater millions of years later. The presence of salt-rich mudstones implies that there was a shallow evaporating lake above these rocks. The team inferred that the lake may have been as broad as 22 miles (35 km) in width and as deep as 100 feet (30 m) at one point.

Larger chunks of rock were subsequently brought into Jezero by rapidly moving water from outside the crater, spreading them on top of the delta and around the crater.

NASA's Jet Propulsion Laboratory's postdoctoral fellow, Libby Ives, who oversees the mission, stated that the understanding of Jezero's history's timeline was possible due to Perseverance's up-close observation, crucial to discerning the details from the broader outline seen in orbital images.

The samples that the Perseverance collects are about as large as chalk pieces found in classrooms, which are kept in specialized metal tubes as part of the Mars Sample Return campaign. Scientists can analyze these samples on Earth using sophisticated lab equipment that is too large to transport to Mars. The selection of samples for collection is decided after Perseverance uses an abrasion tool to remove a patch of a potential rock and then assesses its chemistry using precise scientific instruments, such as the Planetary Instrument for X-ray Lithochemistry, or PIXL, built by JPL.

One of the team's targeted areas, 'Bills Bay,' was abundant with carbonates—minerals that originate in water environments with conditions capable of preserving organic molecules. These rocks also housed a good amount of silica—a material that is great at preserving organic molecules, including that of life.

JPL's Morgan Cable, the deputy principal investigator of PIXL stated, 'On Earth, this fine-grained silica is usually found in areas that were once sandy. This is the sort of environment where, on Earth, traces of ancient life could be preserved and discovered later.'

While Perseverance has instruments capable of detecting miniature, fossil-like structures and chemical alterations that may have been caused by ancient microbes, there is no evidence of either found as of yet.

At an area called 'Ouzel Falls,' of interest to PIXL, the instrument identified the existence of iron associated with phosphate—a component of DNA and cell membranes of all known terrestrial life, and plays a part in a molecule that aids cells in energy transportation.

After arriving at conclusions about each of PIXL's findings on these abrasion patches, the team ordered for the collection of rock cores in the nearby locations: Lefroy Bay was collected alongside Bills Bay, and Otis Peak at Ouzel Falls.

'We have ideal conditions for finding signs of ancient life where we find carbonates and phosphates, which point to a watery, habitable environment, as well as silica, which is great at preservation,' Cable said.

Perseverance's work is, of course, far from done. The mission's ongoing fourth science campaign will explore Jezero Crater's margin, near the canyon entrance where a river once flooded the crater floor. Rich carbonate deposits have been spotted along the margin, which stands out in orbital images like a ring within a bathtub.

Provided by JPL/NASA