MIT model explains how the brain can learn novel tasks while still remembering what it has already learned.
Louis Pasteur once said about science that "chance favors only the prepared mind." His words rang true for Professor John Grotzinger this year, when he began analyzing images of Mars rocks for NASA.
After studying rocks found near the landing site of the rover Opportunity, Grotzinger and other NASA scientists reached the conclusion that Mars had once been a watery place with a flowing saltwater sea. And with that conclusion, scientists leaped over the first major hurdle to answering the larger question: Could life as we know it ever have existed on another planet?
They were able to reach their conclusion about Mars water, in part, through a serendipitous confluence of the work of three faculty members in the Department of Earth, Atmospheric and Planetary Sciences.
Professor Maria Zuber is responsible for accurately mapping Mars and helping select the rover's landing site. Grotzinger joined the NASA science team as a geologist, and has served as leader of the long-term rover planning group much of the time because of the mission's increasing emphasis on geology. Professor Emeritus John Southard wrote a paper more than a decade ago in which--just for fun in the last three paragraphs--he analyzed the hypothetical effect of Mars gravity on water flowing over rock.
The rover landed in a crater near Grotzinger's favorite type of rock--sedimentary with cross-bedding characteristics--and he used his familiarity with Southard's paper to reach the conclusion that Mars once had large seas of flowing surface water.
"Of all the rocks in all the craters on all the planets, the rover just happened to land near Last Chance," Grotzinger said about Opportunity's landing in an outcrop of sedimentary rock, which is formed in layers laid down by flowing water or air currents. (They gave the rock its name in the hope that it wasn't their last chance to pin down the answer.)
"Our observations fit together in a very specific way to make a strong case for flowing surface water. And John Southard's work of 15 years ago created the whole basis for us to be able to make this determination," he said. "I was able to pull out Southard's paper and say [to the other scientists on the NASA panel] 'Look, guys, I'm not making this up. There's a whole lot of rigorous science behind this.'"
Why did Southard choose to use Mars gravity in that paper? His answer: Why not? Basic scientific research is often pursued on a hunch.
"I got such a chuckle out of this," Southard said after the NASA announcement. "Here's something I did 15 years ago for no particular reason, and it finally turns out to be useful."
Grotzinger, who has been working at NASA's Jet Propulsion Lab in Pasadena, Calif., had shared with Southard some of Opportunity's photos during his analysis. When he e-mailed Southard one of the photos that clearly showed the characteristics consistent with a current of surface water, Southard responded with enthusiasm.
"When I looked at the photo, I took a breath and said 'Wow!' To me it looks clearly like ripple trough cross-lamination, in a view at a small angle to flow orientation (i.e., a largely transverse-to-flow view)," Southard said in his e-mail to Grotzinger, drawing on his paper from the September 1990 issue of the Journal of Sedimentary Petrology entitled "Bed Configurations in Steady Unidirectional Water Flows. Part 3: Effects of Temperature and Gravity."
Grotzinger said the entire process has been an amazing one for him.
"Science is driven by key observations. Rarely in Earth sciences does somebody find something early on in a career that changes the way people think of things. You have to roll up your sleeves and work for years or decades to make an important observation," said Grotzinger. "What happened last month is that we got a huge jump on those years and decades.
"It's the kind of thing you can dream about, but when you sit there in the quiet moments writing a proposal, if you go through all the things that you hope you might find, you're at risk of not being funded. So you keep your list small and suggest, for instance, that the Mars rover mission might find some signs of [the planet] having sedimentary rock. I never really imagined when I signed up that I would be working on sedimentary rocks, let alone cross-bedding," he said.
Of course, many other MIT researchers and alumni have contributed to the success of NASA missions since the space agency's inception. MIT has spawned more alumni astronauts than any other nonmilitary institution, and the Department of Aeronautics and Astronautics has played a major role over the years. Aero/astro alumna Jennifer Harris Trosper (S.B. 1990) is mission manager for the Spirit rover, which landed on Mars just a few weeks after Opportunity to explore another crater.
Speaking of craters, Grotzinger said that Opportunity is now heading toward Endeavor, a large crater at least 100 meters wide, to discover if the rock there was laid down in deep or shallow water.
He's concerned that the rocks on the rim of Endeavor may form a cliff too steep for the rover to climb down and back up again.
"If that's the case, we'll switch to the 'roach motel' option," said Grotzinger. "Remember that old TV commercial--'The roaches can check in but they can't check out'? The rover may be able to find a safe way to descend into the crater, but that path might be too steep to allow it to exit. Once we're in, we can make observations of the outcrop, but we won't be able to get back out again.
"The science better look really good in there to justify this. But things do look good from a distance, so I think this is a serious option. If a navigable path is sighted when we arrive at the rim, this will no doubt be the hardest decision our team has made yet," he said.
A version of this article appeared in MIT Tech Talk on April 14, 2004.