NASA’s Perseverance rover hunts for microbes on Mars

The word astrobiology may conjure up images of aliens like the shrill, claw-fearing aliens from Toy Story franchise, Star Trek the logical Vulcan Spock or the hungry Grogu from The Mandalorian. But the first real signs of life and evolution in the universe will most likely come from microbes and rocks.

Astrobiology is also a key goal of NASA’s current Perseverance rover mission. One of the mission’s key initiatives, which began when the rover launched in 2020, is to capture samples that may contain signs of ancient microbial life. The rover is on its second science campaign, collecting rock core samples in Jezero Crater on Mars. Scientists have long believed that this 28-mile-wide crater may be the best prospect for finding signs of ancient microbial life on the Red Planet. The rover has collected four samples of an ancient river delta in the crater since July 7, bringing the total number of “scientifically conclusive” rock samples from the mission to 12.

“We chose Jezero Crater for Perseverance to study because we thought it had the best chance of providing scientifically excellent samples—and now we know we sent the rover to the right place,” said Thomas Zurbuchen, NASA’s associate administrator for science at Washington, in a press release. “These first two science campaigns have yielded an incredible variety of samples to be brought back to Earth by the Mars Sample Return Campaign.”

[Related: Happy Mars-iversary, Perseverance.]

3.5 billion years ago, Jezero Crater was home to an ancient delta or fan-shaped area once at the confluence of a Martian river and lake. Perseverance examines the delta’s sedimentary rocks, which were formed when particles of various sizes settled in the once watery river. The rover explored the crater floor during its first science campaign in 2021 and discovered igneous rocks that form deep underground from magma or during volcanic activity on the planet’s surface.

NASA’s Perseverance rover uses its robotic arm to work around a rocky outcrop called “Skinner Ridge” in Mars’ Jezero Crater. CREDIT: NASA/JPL-Caltech/ASU/MSSS. NASA/JPL-Caltech/ASU/MSSS

“The delta, with its diverse sedimentary rocks, contrasts beautifully with the igneous rocks — formed by magma crystallization — found on the crater floor,” Perseverance project scientist Ken Farley of Caltech in Pasadena, California, said in a news release. “This mapping provides us with a rich understanding of the geologic history since the formation of the crater and a diverse set of samples. For example, we found sandstone that carries grains and rock fragments created far from the Jezero crater – and mudstone that includes intriguing organic compounds.

Within the crater, Wildcat Ridge is a cliff about 3 feet wide that probably formed billions of years ago when mud and fine sand settled in an evaporating saltwater lake. The rover scraped a portion of the surface of Wildcat Ridge on July 20 to analyze the area with the Habitable Raman & Luminescence for Organics and Chemicals (SHERLOC) scan.

The SHERLOC analysis shows that the Martian rock samples contain “a class of organic molecules that are spatially related to those of sulfate minerals.” These sulfate minerals, found in layers of sedimentary rock, can provide inside the water worlds in which they formed.

Organic molecules are made up of a wide variety of compounds, but they are mostly composed of carbon and usually include hydrogen and oxygen atoms. Certain organic compounds are the actual chemical building blocks of life, and the presence of these specific molecules is considered a potential biosignature. These biosignatures are a substance or structure that is possible evidence of past life, but may also have been produced without the presence of life.

[Related: Is there life on Mars? TBD. But scientists found ancient organic matter in the Red Planet’s rocks.]

NASA’s Curiosity rover found evidence of organic matter in rock dust samples in 2013, and Perseverance found organic matter in Jezero Crater in 2021.

“In the distant past, the sand, mud and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have flourished,” Farley said. “The fact that the organic matter was found in such a sedimentary rock – known for harboring fossils of ancient life here on Earth – is significant. However, as capable as our instruments aboard Perseverance are, further conclusions about what is contained in the Wildcat Ridge sample will have to wait until it is returned to Earth for in-depth study as part of the campaign the Mars Sample Return Agency.”

In September 2021, the NASA-ESA (European Space Agency) Mars sample return campaign began when Perseverance retrieved its first rock sample. The rover has since collected one atmospheric sample and two witness tubes, all of which are stored in the rover’s belly.

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