Sep 20, 2022 - Science

Confirming life on Mars will take more than just a rock sample

Illustration of multiple microscope lenses examining a microscope slide.

Illustration: Aïda Amer/Axios

If NASA finds signs of extinct life on Mars, it may be difficult to confirm it is actually what scientists have been seeking for decades.

Why it matters: Finding life on another planet would change our view of what it means to exist in the universe, but an extraordinary, life-altering discovery also requires extraordinary evidence.

  • "The burden of proof for establishing life on another planet is very, very high," NASA's Ken Farley, Perseverance project scientist, said during a news conference last week.

Driving the news: NASA scientists announced last week that the Perseverance rover on Mars had cached intriguing samples that may be able to tell researchers whether the Red Planet was once inhabited.

  • The rocks were gathered in the Jezero Crater, which is thought to be the site of a river delta billions of years ago. They contain organic compounds — molecules that have carbon and hydrogen but can also contain oxygen and other elements — that can be created by living organisms or other natural processes like the interactions of water with rocks over time.
  • One of those samples, taken from a rock named Wildcat Ridge, probably formed "as mud and fine sand settled in an evaporating saltwater lake," NASA said in a statement. Perseverance analyzed the rock with its SHERLOC instrument, revealing it contains a higher amount of organic compounds than any other sample gathered so far.
  • "We are looking at rocks that were deposited in a habitable environment, with good preservation potential at a time on Earth when life already existed," Farley said in an interview with Axios.

Still, scientists will have to wait until that sample and others are back on Earth to find out whether those compounds mean life once thrived on Mars.

How it works: Once back on Earth, scientists will use high-powered laboratory tools to analyze the samples.

  • Those tools are far more powerful than any instruments researchers are currently able to send to Mars aboard a relatively small rover, increasing the odds of figuring out if any given organic compound is from life.
  • If one lab were to come across what they think could be a biosignature inside one of these samples, they would likely need to call in another lab to examine the context of the finding, including what kind of rock it was found within, Farley said.

The intrigue: In order to determine whether these samples contain evidence of life, scientists will need to assess any degradation of the sample from Mars' extreme environment and confirm their findings with multiple tools.

  • This is effectively a new kind of science, so actually defining what qualifies as a true signature of life is going to be a challenge in and of itself.
  • Organic compounds also degrade over time with exposure to space radiation, which constantly bombards Mars. Scientists have to contend with the natural radioactive decay of elements like uranium and potassium also found on Mars.
  • "Inevitably, the organic molecules will have seen a lot of ionizing radiation, and this means we are not looking for proteins. We're not looking for DNA," Farley said. That will make it more challenging to actually confirm that the organics that scientists are studying were created by life.

What to watch: NASA is expected to launch its Mars sample return orbiter in 2027, with the lander for the mission launching the next year.

  • Once there, NASA is planning to load up the cached Perseverance samples onto the lander. If all goes to plan, the samples should be back on Earth by 2033.
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