Curiosity doesn’t go deep enough for its soil samples to contain life (Image: NASA/JPL-Caltech/MSSS)

No one has looked for life on Mars for more than 30 years, ever since NASA’s Viking missions sent back inconclusive results. Genomics maverick Craig Venter wants to change that. Cracker of the human genome and builder of synthetic life, Venter announced at the Wired Health Conference in New York last week that he wants to send a DNA sequencer to Mars and beam back the genomes of any alien microbes.

Details of this ambitious plan are slim, and Venter has declined to elaborate. But there is reason to think Mars DNA can be found – if we know how and where to look.

Previous hunts for life, including the experiments on the Viking landers, looked for organic molecules on Mars’s surface. The results have been plagued by ambiguity, especially in the light of growing evidence that organic molecules can be formed by natural processes that do not involve life.


Finding DNA would be a much more direct indicator of life, and there is a chance it is out there. The precursors to ribose – the sugar found in DNA and RNA – have been detected in interstellar space, and complex organic molecules have been found on Saturn’s moons Titan and Enceladus. Life’s raw materials could have spread throughout the early solar system, and life may have emerged several times from a common set of ingredients.

Alternative chemistry

It’s also possible that life hitched a ride between Earth and Mars in their early days. Asteroid impacts have sent about a billion tonnes of rock careering between the two planets, potentially carrying DNA or its building blocks. That could mean that any genetic material on Mars is similar enough to DNA that we have a chance of finding it using standard tests.

Even if we don’t, we can set up future sequencers to look for molecules that use alternative sugars or chemical letters in the genetic code. “We’re not there yet, but it’s not a fundamental limitation,” says Chris Carr of the Massachusetts Institute of Technology, who works on the NASA-backed Search for Extraterrestrial Genomes.

Another option is for a DNA sequencer to piggyback on an organics-hunting suite. Searching only for DNA as we know it means we might miss alternate life-forms, says Michael Meyer, lead scientist for NASA’s Mars Exploration Programme. A sequencer could follow up on an organics find by looking for DNA and testing whether any found has earthly origins.

Secret tunnels

Since Viking, though, NASA has mostly played it safe, scouring Mars’s surface not for the chemical signatures of life but for ancient habitable environments – the goal of the Curiosity rover. NASA has gone this route because Mars lacks a thick atmosphere and protective magnetic field, so it is exposed to damaging ultraviolet light and cosmic rays. Any life would have to be shielded under at least a metre of soil or rock to survive. What’s more, recent work has shown that DNA breaks down at a predictable rate. That rules out any genetic traces more than a million years old surviving.

Venter’s plan would need to target more fertile hunting grounds deeper inside Mars. Luckily, the technology to do that may already exist. The European Space Agency’s ExoMars mission, slated to launch in 2018, will have a drill that will delve at least a metre deep. Robot explorers might also aim for lava tubes, tunnels excavated by ancient volcanic flows and shielded from radiation. NASA’s Jet Propulsion Laboratory is already developing a rover called Axel that can abseil down cliffs and could head into a Martian cave.

If a DNA sequencer is flight-ready when the next Mars rover launches, would NASA consider adding it in? “Of course,” Meyer says. “It certainly is a worthy cause.”