Issue 016

What we can learn from water on Mars

The question of whether there is water on the red planet has kept scientists curious for decades. James W. Head, a planetary geologist at Brown University who has worked with NASA on the Apollo program and several missions to Mars, says that water on the planet might indicate the discovery of life, but what's more important is why there is hardly any water at all.GOOD: What's so interesting about water on Mars, at a basic level?JAMES Head: There are a couple of compelling questions about Mars that drive a lot of the exploration and interest. [One is] the origin of life-is there any evidence on Mars for life?-because it does have many of the conditions, like the presence of water, organic material, stuff like that, that could lead to life. That's one big deal. The second is simply what's going on with the evolution of water on Mars. We see Mars now as an extremely cold, very arid desert. And then we see in the geological record huge channels, floods across the surface, maybe even oceans in the northern lowlands.GOOD: And what made it go from a place where there were oceans and rivers to the environment that it has now?JH: That's actually what we are studying right now, because somewhere about a billion years into the history of the planet, something changed very rapidly, and led to it being a cold, hyper-arid desert. We go to Antarctica a lot because it has the most Mars-like conditions on Earth. It's really cold, and windy, and extremely dry. How did Mars go from looking more like Earth to looking like an extreme environment today? That is another part of our search for water on Mars: so we can study climate change. We don't know the answer yet, but it is pretty compelling. Considering what is happening here on the Earth, it's like, Hmm, I wonder if this could be happening here.GOOD: So what does it mean that there is water on Mars? Why is it important?JH: One reason is, again, the origin of life and the conditions that lead to the formation and evolution of life. We don't have a clue. The second is climate change. Surely humans are inducing changes in the [Earth's] climate, but how extreme do things get? What happens when you really stress out a system? Does it modify a little bit, or does it really go through a major irreversible change, for example? And so by studying Mars, we are really looking [at] changes in ubiquity, because they are so extreme. It's like performing an experiment you wouldn't want to perform on the Earth.GOOD: And we've found ice under the surface of the planet, right?JH: Yes. And a lot of that ice is sequestered in different ways at different latitudes, and that provides us with an opportunity to go look at 200-million-year-old ice. What was the atmosphere like 5, 7, 8 million years ago? If you can find a piece of ice that old, it will have bubbles in it which will have captured the atmosphere, so that's what we are trying to do down there.

"If you can find the liquid water-and maybe it is below the poles-maybe that's where life is."

GOOD: And what would it mean if we found liquid water under the surface? How does that change what we know about Mars?JH: Well, I think the biota that evolves in liquid water is much different than the one that evolves in ice. In ice, organisms can live but they are a little bit more in stasis. But if we can find that there is a global groundwater system that still exists today, I would bet big money that if there is ever life on Mars, that is where it is going to be. So if you can find the liquid water-and maybe it is below the poles-maybe that's where life is. We find it in extreme environments in Antarctica. It's incredible.GOOD: What's next?JH: In 2011, there is a Mars science laboratory which is going to be a huge, very sophisticated rover, which is going to have a lot of instruments on board, like mass spectrometers and other types of things that can help to detect the gases and other things that are indicative of life, and understand the mineralogy a lot better.GOOD: So when are we going to go and drill through the ice caps and see if there is water under them?JH: Well, we're trying to interest NASA in such a mission. We have a mission that would deploy a drill onto the ice cap and would make measurements. One of the things about the NASA community is that the investigators have a lot of input on the next missions coming up, so we're currently in the process of arguing about what ought to be the missions in the next 20 years.