SCIENCE

Maria Zuber

On the surprise evidence of flowing water on Mars

February 2007

The Mars Global Surveyor just went dark after circling mars for ten years. What were its most important findings?

We made the first viable model of the internal structure of Mars—including that the core of Mars is probably still fluid. Another experiment found signs of hematite, a mineral sometimes formed in the presence of water. The most recent discovery was evidence for liquid flowing water on the surface. If you look year to year, you see evidence that the surface has changed. New gullies appear, and you see them only in places where the temperature rose above the melting point of water. This caused a big change in our thinking because all the theories said it shouldn't be possible to have liquid water on the surface of Mars because today the atmosphere is so thin. Of course, it has fascinating implications for whether or not life might ever have developed there.

Can you drink the water?

It probably has salts and other minerals in it. It would be like drinking acid mine water. But you can purify water. Someday, when we send people to Mars, it'll be much easier to send devices that melt ice and purify water than it would be to send water with them.

What are the big questions about Mars that remain? Where did the water go? And what caused the climate to change so that Mars lost much of its atmosphere 3.8 billion years ago?

Today, a quarter of the Martian atmosphere condenses into the polar caps as snow each year, then goes back into the atmosphere. The snow isn't water ice; the atmosphere is carbon dioxide, so Mars snows dry ice.

You advised the Bush administration on what science astronauts might do on Mars.

You'll never be able to justify sending humans to Mars simply for scientific purposes, because you'll always be able to design robotic experiments that provide great science at a lower cost. So the rationale for sending humans is exploration. However, once humans are there, I believe there will be discoveries they can make that robots can't. For example, if life does exist on Mars, it could be deep within the crust, where it's warmer than on the surface. If that's the case, you have to drill deep within the crust, and you're not going to be able to do that with robots.

If it were possible, would you go to Mars?

Can I wait until I get my kids through college? Yeah, I sure would. But a more practical goal for me is to have one of my students go. One of these days, somebody I've taught and trained, I hope, will walk on Mars.