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Mars: promising biosignatures, synonymous with life, found by Perseverance

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NASA’s Perseverance rover is engaged in its second science campaign, collecting rock samples from a specific area that previously harbored water. The latest findings provide more detail about this region, with rocks showing a class of organic molecules typical of potential biosignatures of life. The return of the samples to Earth will make it possible to confirm or not these first promising indications.

A key focus of Perseverance’s mission to Mars is astrobiology, including collecting samples that may contain signs of ancient microbial life. The rover will characterize the planet’s past geology and climate, pave the way for human exploration of the Red Planet, and be the first mission to collect Martian rocks. Subsequent NASA missions, in cooperation with ESA, will send spacecraft to Mars to collect these sealed samples and return them to Earth for further analysis.

Additionally, the Mars 2020 Perseverance mission is part of NASA’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.

Currently, the rover is entering its second science campaign, specifically targeting a region long considered by scientists to be an excellent prospect for finding signs of ancient microbial life on Mars. These findings are promising.

A page open to the past

So NASA’s Perseverance rover put its robotic arm to work around a rocky outcrop called “Skinner Ridge” in the 45-kilometre-wide Jezero crater. It is home to a delta — an ancient fan-shaped feature that formed about 3.5 billion years ago at the convergence of a Martian river and lake.

Before taking samples, the rover explored the floor of the crater, finding igneous rock, which forms deep underground from magma or during volcanic activity on the surface. Currently, Perseverance studies the sedimentary rocks of the delta, formed when particles of different sizes were deposited in the once aquatic environment.

Ken Farley, Perseverance project scientist at Caltech in California, explained in a press release: The delta, with its various sedimentary rocks, contrasts beautifully with the igneous rocks — formed from the crystallization of magma — discovered at the bottom of the crater “. The robot has collected four samples there since July 7, bringing the total number of rock samples to 12.

Thomas Zurbuchen, NASA Associate Administrator for Science in Washington, says: We chose to explore Jezero Crater because we thought it had the best chance of yielding scientifically excellent samples — and now we know we sent the rover to the right place. These first two scientific campaigns produced an incredible diversity of samples to bring back to Earth as part of the Mars Sample Return campaign. “.

This area, thanks to the juxtaposition of different rocks, provides scientists with a large part of the geological history after the formation of the crater. Ken Farley points out: For example, we found sandstone that carries grains and rock fragments created far from Jezero Crater – and mudstone that includes intriguing organic compounds “.

Subsequently, the rover aimed for “Wildcat Ridge”, a rock about a meter wide. It was probably formed billions of years ago, when mud and fine sand were deposited in an evaporating saltwater lake. On July 20, the rover abraded part of the surface of Wildcat Ridge so that it could analyze the area with the SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument.

Two chalk-sized rock cylinders inside NASA’s Perseverance rover drill rig, taken from the ‘Wildcat Ridge’ outcrop in Mars’ Jezero Crater. ©NASA

SHERLOC analysis indicates that the samples exhibit a class of organic molecules that are spatially correlated with those of sulfate minerals. Sulfate minerals found in sedimentary rock layers can provide important information about the aquatic environments in which they formed.

Signs of life?

However, a biosignature—a substance or structure that could be evidence of past life—does not necessarily mean the presence of life. Indeed, organic molecules consist of a wide variety of compounds, consisting mainly of carbon and generally comprising hydrogen and oxygen atoms, but also nitrogen, phosphorus or sulfur. All of these molecules can be produced by chemical processes without the presence of life.

However, the geographic location of the current samples makes it more than likely that they are indeed real biosignatures. Farley explains: In the distant past, the sand, mud and salts that now make up the Wildcat Ridge sample were deposited in conditions where life could have thrived. The fact that organic matter was found in such sedimentary rock — known to preserve fossils of ancient life here on Earth — is”.

Not to mention that in its analysis of Wildcat Ridge, the SHERLOC instrument recorded the most abundant organic detections of the mission to date.

Return trip

However, as efficient as the instruments on board Perseverance are, it will be necessary to wait for the return to Earth for an in-depth study as part of NASA’s Mars Sample Return campaign.

Incidentally, the first stage of the sample return campaign began when Perseverance cored its first rock sample in September 2021. In addition to its rock samples, the rover collected an atmospheric sample and two control tubes, all stored in the rover. The latter will have to transport them and then deposit them near the base of the delta in about two months. Then he will continue his exploration.

rover sample card
This image shows two locations in Mars’ Jezero Crater where NASA’s Perseverance rover collected rock samples for possible return to Earth in the future. “Wildcat Ridge” lower left and “Skinner Ridge” upper right. ©NASA

Laurie Leshin, director of NASA’s Jet Propulsion Laboratory, concludes: The fact that we are weeks away from deploying the fascinating Perseverance samples and only a few years away from arriving on Earth so that scientists can study them in exquisite detail is truly phenomenal. We will learn so much “.

mars recovery mission
Illustration of the concept of returning samples to Mars. © NASA/JPL-Caltech

With planned launch dates for Earth Return Orbiter and Sample Retrieval Lander in fall 2027 and summer 2028, respectively, samples are expected to arrive on Earth in 2033. This advanced mission architecture will include two sample retrieval helicopters .