NASA’s Perseverance rover deciphers ancient history of Martian lake

Marking its 1,000th Martian day on the Red Planet, NASA’s Perseverance rover recently completed its exploration of the ancient river delta that contains traces of a lake that filled Jezero Crater billions of years ago years. The six-wheeled scientist has collected a total of 23 samples to date, revealing the geological history of this region of Mars.

One sample called “Lefroy Bay” contains a large amount of fine-grained silica, a material known to preserve ancient fossils on Earth. Another, “Otis Peak,” contains a significant amount of phosphate, often associated with life as we know it. Both of these samples are also rich in carbonate, allowing for a record of environmental conditions since the rock was formed.

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

“We chose Jezero Crater as a landing site because orbital imagery showed a delta, clear evidence that a large lake once filled the crater. A lake is a potentially habitable environment, and the delta rocks are an environment ideal for burying signs of ancient life in the form of fossils in the geological record,” said Ken Farley, Perseverance Project scientist at Caltech. “After extensive exploration, we pieced together the geological history of the crater, tracing its lake and river phase from start to finish.”

Jezero was formed following an asteroid impact nearly 4 billion years ago. After Perseverance landed in February 2021, the mission team discovered that the crater floor consisted of igneous rocks formed from underground magma or volcanic activity on the surface. They have since discovered sandstone and mudstone, signaling the arrival of the first river in the crater hundreds of millions of years later. Above these rocks are salt-rich mudstones, signaling the presence of a shallow lake rife with evaporation. The team believes the lake eventually grew to a width of up to 35 kilometers in diameter and a depth of up to 30 meters.

Later, fast-flowing water carried boulders from outside Jezero, distributing them across the top of the delta and elsewhere in the crater.

“We were able to see a general overview of these chapters of Jezero’s history in orbital images, but it took getting closer to Perseverance to really understand the timeline in detail,” said Libby Ives, a postdoctoral researcher at the Jet Propulsion Laboratory. of NASA in the South. California, which manages the mission.

Tempting samples

The samples collected by Perseverance are about as large as a piece of classroom chalk and are stored in special metal tubes as part of the Mars Sample Return campaign, a joint effort of NASA and ESA (Agency European Space Agency). Bringing the tubes to Earth would allow scientists to study the samples with powerful laboratory equipment, too large to take to Mars.

To decide which samples to collect, Perseverance first uses an abrasion tool to wear away a patch of a potential rock, then studies the rock’s chemistry using precision scientific instruments, including the Planetary Instrument of X-ray lithochemistry built by JPL, or PIXL.

On a target the team calls “Bills Bay,” PIXL spotted carbonates, minerals that form in aqueous environments with conditions likely to be favorable for the preservation of organic molecules. (Organic molecules form through geological and biological processes.) These rocks were also abundant in silica, an excellent material for preserving organic molecules, including those linked to life.

“On Earth, this fine-grained silica is what you often find in a formerly sandy place,” said JPL’s Morgan Cable, PIXL deputy principal investigator. “This is the kind of environment where, on Earth, the remains of ancient life could be preserved and later found.”

Perseverance’s instruments are able to detect both microscopic structures resembling fossils and chemical changes that might have been left behind by ancient microbes, but they have yet to find evidence of either.

On another target examined by PIXL, called “Ouzel Falls,” the instrument detected the presence of iron associated with phosphate. Phosphate is a component of the DNA and cell membranes of all known terrestrial life and is part of a molecule that helps cells transport energy.

After evaluating PIXL’s results on each of these abrasion zones, the team sent commands to the rover to collect nearby rock cores: Lefroy Bay was collected next to Bills Bay and the Otis Peak at Ouzel Falls.

“We have ideal conditions for finding signs of ancient life where we find carbonates and phosphates, which indicate a watery, habitable environment, as well as silica, which is excellent for preservation,” Cable said.

Perseverance’s work is, of course, far from done. The mission’s fourth ongoing science campaign will explore the margin of Jezero Crater, 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 in a bathtub.