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Why Go to Mars

Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, is an astrophysicist and the author of numerous books and articles about space. In early 2004, he was appointed by President George W. Bush to serve on the President's Commission on Moon, Mars and Beyond, a nine-member panel designated to offer recommendations on how best to implement the president's vision for future space exploration. Science Bulletins caught up with Tyson recently in his office on the fifth floor of the Museum's Rose Center for Earth and Space.

Neil deGrasse Tyson (Director, Hayden Planetarium) 

Why go to Mars?

Mars has a 24-hour day. It has polar ice caps. Its axis is tilted compared with its orbit, just as Earth is tilted on its axis. That means Mars goes through seasons, just like Earth. Mars, as cold as it is, is not as oppressive an environment as almost any other place we can think of going in the Solar System. From a runaway greenhouse effect, Venus is 900 degrees Fahrenheit and would melt or vaporize most things you sent to its surface. Mercury is also very hot, being close to the Sun. So when you look at the nearby terrestrial planets, Mars is looking … just right, in spite of the challenges.

While that alone might make a trip to Mars compelling, it's far from the most compelling reason. We learned in the 1960s that Mars's surface has features that, as far as we can tell, can only have been made in the presence of water: standing water, running water, deluging water. There are features that look like they're floodplains. There are riverbeds that are straight and riverbeds that meander. Combine all of this, and you consider how important water is to life on Earth, you can't help but speculate that Mars was once a really wet place, possibly even harboring life at one point. So much of what drives cosmic exploration involves the quest to learn whether or not we're alone in the Universe — as an intelligent species, or as life at all. Mars being so close compared with the rest of the cosmos — it's a slam dunk as a place you want to go visit.


What have Spirit and Opportunity, NASA's two Mars Exploration Rovers, been discovering up there?

Until now, all the evidence for water on Mars has been strongly circumstantial. It looks like water was there, because the surface features resemble features on Earth that we know are made by water. But you don't really know until you analyze the rocks. And geologists are good at that. Geologists can look at a rock and tell you a whole story: how old the rock is, what happened to it while it formed, how it got there. They do this with clever, subtle measurements of the rock's structure, form, and chemical composition. So geologists can read the history of the rocks of Mars and thereby read the history of the Martian surface. And the most recent evidence from the rovers confirms what we strongly thought before, that in fact water enjoyed a major presence on Mars.

Of course, what's really driving the missions to Mars is the search for life; there's no question about it. The current rovers aren't carrying biological experiments; they're carrying chemical experiments. One of the chemical experiments involves identifying certain kinds of rocks that can form only in the presence of water. Those rocks were found-so that's an important first step.

Suppose fossils or other signs of life are discovered on Mars. What are the implications?

There are two implications: one extraordinary, the other fun but not extraordinary.

There is evidence to suggest that Mars was wet before Earth was wet. If that's the case, maybe Mars had life before Earth had life. We know that meteors jump between the planetsa fact established only in the past ten years, or so. A big meteor hits Mars, and thrusts rocks into space that then land on Earth; we know that this happens. We also know that certain classes of bacteria have very high thresholds for radiation and for temperature: they're extremophiles, they love extremes. Combine the fact that extremophiles exist, that rocks move from planet to planet, and that Mars was wet before Earth was wet, and you have to admit the possibility that life traveled from Mars to Earth as stowaways in the cracks of rocks. Which would make all humans — all life on Earth — the descendants of Martians.

Now, that's fun but not extraordinary, because we don't learn anything new about biology. We would all share common DNA. Biologists would continue to revel in the biodiversity of life as we know it, but at the end of the day there'd still be only a sample of one: DNA-based life. Whereas if the identify of life on Mars were encoded by other means, there'd be no end of inquiry, no end of revolutionary research — we will have discovered the first truly new form of life.

What do you think are the odds of finding evidence of life on Mars?

High — certainly higher than 50 percent. And by life, I refer to fossil life, not current life; and simple life, bacteria or microbes. Water is the key.