NASA’s Perseverance Rover celebrates 1000th day

Reaching its 1,000th day on Mars, NASA's Perseverance rover recently concluded its investigation of the old river delta. This area contains signs of a lake that existed in Jezero Crater billions of years ago. The rover has collected 23 samples so far, shedding light on the geological past of this Martian region.

One sample, named “Lefroy Bay,” includes a substantial amount of fine-grained silica, a substance known for preserving ancient fossils on Earth. Another sample, “Otis Peak,” contains a considerable quantity of phosphate, often linked with life. Both samples are rich in carbonate, indicative of the environmental conditions when the rock was formed.

These findings were presented on 12 December at the American Geophysical Union fall meeting in San Francisco.

Ken Farley of Caltech, the Project Scientist for Perseverance, said: “We picked 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 delta rocks are a great environment for entombing signs of ancient life as fossils in the geologic record. After thorough exploration, we’ve pieced together the crater’s geologic history, charting its lake and river phase from beginning to end.”

Jezero formed nearly 4 billion years ago due to an asteroid impact. Following Perseverance's landing in February 2021, the mission team found that the crater's floor is composed of igneous rock, formed from underground magma or surface volcanic activity. They later discovered sandstone and mudstone, indicating the presence of the first river in the crater hundreds of millions of years later. Salt-rich mudstones above these rocks suggest a shallow lake undergoing evaporation. The team believes the lake eventually spanned up to 22 miles (35 kilometres) in diameter and reached depths of 100 feet (30 meters).

Subsequently, rapid water flow brought in boulders from outside Jezero, dispersing them across the delta and other areas of the crater.

Libby Ives, a Postdoctoral Fellow at NASA’s Jet Propulsion Laboratory, which manages the mission, stated: “We were able to see a broad outline of these chapters in Jezero’s history in orbital images, but it required getting up close with Perseverance to really understand the timeline in detail.”

Compelling samples

Perseverance stores its samples, each about the size of classroom chalk, in special metal tubes as part of the Mars Sample Return campaign, a collaborative effort between NASA and ESA (European Space Agency). Returning these tubes to Earth would allow scientists to analyse the samples with advanced lab equipment, too large for transportation to Mars.

To select samples, Perseverance first uses an abrasion tool on a prospective rock, then examines the rock’s chemistry with precision instruments, including the JPL-developed Planetary Instrument for X-ray Lithochemistry, or PIXL.

At a site called “Bills Bay,” PIXL identified carbonates – minerals formed in water-rich environments potentially favourable for preserving organic molecules. These rocks also contained an abundance of silica, excellent for preserving organic molecules, including those related to life.

JPL’s Morgan Cable, the deputy principal investigator of PIXL, commented: “On Earth, this fine-grained silica is what you often find in a location that was once sandy. It’s the kind of environment where, on Earth, the remains of ancient life could be preserved and found later.”

Although Perseverance's instruments can detect microscopic, fossil-like structures and chemical changes possibly left by ancient microbes, they have not yet found evidence of either.

At another site, “Ouzel Falls,” PIXL detected iron associated with phosphate. Phosphate is a component of DNA and cell membranes of all known terrestrial life, and part of a molecule vital for cellular energy transport.

After analysing PIXL’s data on each abrasion patch, commands were sent for the rover to collect rock cores nearby: Lefroy Bay next to Bills Bay, and Otis Peak at Ouzel Falls.

Cable noted: “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.”

Perseverance's mission continues, with its fourth science campaign aiming to explore Jezero Crater’s edge, near the canyon entrance where a river once flowed into the crater floor. Notable carbonate deposits have been observed along the margin, visible in orbital images like a ring inside a bathtub.

Further information about the mission

A principal goal of Perseverance's mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will detail the planet’s geology and past climate, contribute to the preparation for human exploration of Mars, and be the first mission to collect and store Martian rock and regolith (broken rock and dust).

Future NASA missions, in collaboration with ESA, aim to send spacecraft to Mars to retrieve these sealed samples and bring them back to Earth for comprehensive analysis.

The Mars 2020 Perseverance mission is a component of NASA’s Moon to Mars exploration strategy, encompassing the Artemis missions to the Moon, which will aid in preparing for human exploration of Mars.

JPL, managed by Caltech for NASA, constructed and oversees the operations of the Perseverance rover.