Few scientists know Mars as well as Michael Carr, a planetary geologist at the U.S. Geological Survey from 1962 until his retirement in 2004. Carr, 77, who won the National Air and Space Museum’s lifetime achievement trophy in 1994, has influenced just about every NASA mission to Mars since Mariner 9 in 1971, for which he prepared the first global geologic maps of the planet. With co-author David Scott, Carr also showed how the history of Mars could be divided into three general periods, which are used to compare Martian geologic events and processes to those on other terrestrial planets. He is now an advisor to the Mars program office at NASA’s Jet Propulsion Laboratory in Pasadena, California. Author of more than 150 papers and two books on Mars, the native of Leeds, England, is known to colleagues as “Mars Mike,” a nickname he regards with amusement.
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Air & Space: Are there other places in the solar system that deserve as much attention as has been paid to Mars?
Carr: I don’t believe so. The prospect of some form of indigenous life is driving the program, and while there are advocates for life elsewhere in the solar system, such as [Jupiter’s moon] Europa, I do think the prospects are best for Mars.
What sort of strategy would you recommend to explore Mars?
To me, sample return is the essence. Almost everybody involved agrees that what we need to do is get samples back from Mars. We have all this information on topography, surface hydrology, this and that, but the most outstanding unknown is: Is there any life on Mars or was there ever any life? And the only real way to determine that is to bring samples back to Earth and look at them with the most sophisticated instruments that we have.
How many samples would you need?
The mission that was being looked at was to have a rover and bring back on the order of 40 samples that were selected as the rover went around and did different kinds of sampling. We’re only talking about small amounts of material, about 500 grams total [about 1.1 pounds], selected from different locations. I think if there was life, that [information] could be determined from the samples.
More than half of all Mars missions have failed since the first flyby attempt by the Soviets in 1960. Why has Mars been so difficult to reach?
What you’re saying is somewhat deceptive, because if you look at U.S. missions we’ve been remarkably successful. We did have that bad spot [in 1999] when the Mars Polar Lander and the Mars Climate Orbiter failed. But we’ve been successful just one mission after another. And what we’re trying to do at Mars gets more and more difficult because we’ve done the easy things. The Russians have been very, very unsuccessful. Going to Mars, and particularly landing on Mars, is not easy.
Have the Russians given up trying to explore the planet?
They did try recently with the Phobos mission [a failed 2011 attempt to return a sample from the Martian moon Phobos]. I don’t know what the consequences are of their failures, but I suspect they’re having trouble getting their Mars program funded because of the failures. Now we’re getting our program cut despite having success.
What are your thoughts on the White House’s proposal to cut NASA’s budget for Mars exploration?
I’ve spent most of my life, since 1959, studying Mars, so obviously I’m very disappointed. And it’s disappointing too because the program has been so incredibly successful, and Mars is such an interesting place.
The Mars rovers have been getting progressively bigger. How big can rovers realistically get?
I suspect that the MSL [Mars Science Laboratory] is about as big as a robotic rover can get. What’s driving the size? It’s partly the payload, and the power required, and that kind of thing. There is a reason for size. If you’re an ant, it’s hard to get over a big boulder. If you want a rover to last a long time and be able to move over different kinds of terrain, size helps. But as time progresses, the instrumentation get smaller and smaller, so you don’t need as big a rover. Until people go and we have to lug people around, the MSL is about as big as rovers are going to get.
When do you think humans will go?
Certainly not in my lifetime. Maybe 2040 or 2050. There are various studies that are done and just to constrain the study, they have to pick a date. But it’s not a real date. Most of these are looking at 2030, but I don’t think it’s going to happen then.
Here we are in 2012. I can’t believe that 20 years from now humans could be ready to go. The lead time to do something like that is just enormous. And there may be things you can’t speed up, like human factors, the physiological things that we don’t fully understand. A human mission to Mars is a very extended mission. You’re talking about 1,000 days. A lot of stuff has to be solved before you can do that.