03 December 2004

Life on Mars More Likely?

The Mars Exploration Rovers, Spirit and Opportunity, were not designed to find life on Mars. They were designed to learn about Mars' geology and geochemistry.

On 2 December NASA announced several recent findings from Opportunity, in Meridiani Planum, which are published in the latest Science magazine. The abstracts are available here (registration required).

The Opportunity researchers have found conclusive evidence that there was liquid water on Mars in the past. (Summary article from Space.com) So it seems possible that the conditions for life once existed on Mars, and there might be fossil evidence there still. There might even be living organisms on Mars today. (In fact there almost certainly are—carried there on our spacecraft! But let's concentrate on native Martian life.)

These results build on earlier findings that suggested past or present water on Mars:
  • Channels apparently carved by rivers and streams
  • Water ice in Mars north and south polar ice caps
  • Mars Express saw methane, which might or might not be of biological origin.
If there was water on Mars, there might be life on Mars. Current scientific thinking is that life could not arise or evolve without liquid water present. Of, course, the presence of water doesn't guarantee the presence of life, just the possibility. How likely is it that life would have evolved on Mars?

The Earth formed from dust in the disk around the Sun over a period of hundreds of millions of years. We now think that life originated on Earth just as soon as liquid water was able to collect on its surface about 500 million years after the Earth's initial formation.

At the time life is thought to have arisen on Earth, our planet was still highly volcanic, with an atmosphere of carbon dioxide. Seas, if any, were being boiled off periodically by asteroid impacts. Mars was probably in about the same state at the same time. So if life could arise so early on Earth, almost as soon as liquid water could collect from volcanic gasses (and perhaps from comets), then why not on Mars, too?

That possibility raises interesting questions:
  • If there is life on Mars, is it the same as life on Earth? Life on Earth is believed to have arisen just once, and all life evolved from that early event. Could Mars life be from a separate event, with a different genetic code, or even different biochemistry? Could one have arisen from the other, from a single origin? (There was speculation that residues of living organisms from Mars in a meteorite found in Antarctica in 1984.)
  • How can we learn for sure whether there is or was life on Mars? Currently, sample return missions are the best idea.
  • How can we avoid contaminating Earth's biosphere with living organisms possibly brought back from Mars? (We have presumably already contaminated Mars with Earth organisms. A number of non-sterile space probes have landed or crashed on Mars.)
Our fascination with the possibility of life on Mars will continue to be one of the driving forces for exploration of that planet.

Once you have water, is life easy or difficult?

" . . . I'm simply saying that life, uh... finds a way."
Dr. Ian Malcolm
Jurassic Park

What do you think it would mean if we did find life on Mars?

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