William and Mary Alumni Magazine | Winter 2007/2008, Vol. 73, No. 2
Photo by Stephen Salpukas
|
Methane rainstorms, cryovolcanoes spewing out a water-ammonia mix and debate about ethane glaciers are all just part of the unfolding understanding of the mechanics of the exotic geology of Titan, one of Saturn's moons. While Stofan has done a great deal of research on volcanoes here on Earth with Proxemy Research, when the Cassini spacecraft makes its occasional visits to Titan, her concern shifts to the orbit around Saturn -- a distance of more than 746 million miles.
In a presentation to an audience of geology faculty and students -- including her son Ryan, a freshman at William and Mary -- the alumna spoke of the strange conditions on Titan being revealed by radar examination from Cassini.
Stofan, a senior lecturer and honorary professor at the University College of London, was on campus as the lead author on a study of Titan's geology published this year in Nature. She continues to evaluate radar scans of Titan's surface being sent back from the Cassini orbiter, discovering vast lakes of methane on the surface. The depiction of the surface of the satellite is based on applying earthly geological principles to the data received from Cassini and from other sources, notably the Huygens probe sent down from Cassini to the surface of Titan.
"I'm basically a radar geologist," she says. "I'm used to interpreting radar images of planetary surfaces," something she also did in the early 1990s for the Magellan mission to Venus. To the naked eye, Titan looks like a "fuzzy orange tennis ball" and, like Venus, has a thick atmosphere that requires radar to "slice through the clouds," as Stofan puts it.
Titan is of special interest to scientists, she says, because it's a "prebiotic world," with a chemistry based on organic compounds that might eventually produce amino acids. Initially, researchers expected to find a heavily cratered surface, most of which was filled with liquid methane, possibly even a global methane/ethane ocean.
"There has been methane detected in the atmosphere and, for there to be methane in the atmosphere, it has to be replenished from some sort of source on the surface or subsurface," she explains. While on Earth methane is a gas, it's cold enough on Titan to exist as a liquid, complete with a process that mimics the water cycle on our planet.
Titan is so cold, in fact, that it redefines what we know as ice. "You have to stop thinking of it as water ice and think about it as rock, because at 90 degrees Kelvin, water ice is so hard that it behaves more or less like rock does," she says. There was no global ocean as predicted, but plenty of such lakes, including at least one "sea" larger than Lake Superior. Much of the surface so far is exhibiting familiar-looking features, but that doesn't mean it's quite the same.
"Here's this landscape that, in a way, is so Earthlike and so familiar, but at the same time, it's so exotic," she says. "Titan is the first [solar] body that I've worked on where you can find all the processes we have on Earth." Only on Titan, instead of land and water, there's ice and methane.
Stofan was brought up in a science-saturated household. Her father worked for NASA and her mother was a science teacher. "And so from about the time I was 5 or 6 years old, I knew I wanted to be a scientist," she says. "Eventually I decided I wanted to be a geologist, partially because my mother took a geology course when she was doing a master's degree in education. I tagged along on her field trip -- and I loved it!"
She made the most of her father's contacts at NASA, coming to realize that she could keep her head in the sky and her feet on the ground by combining planetary studies and geology into one field.
"I asked a lot of people who were working in the planetary field where I should go for an undergraduate degree -- I knew I also would need to get a Ph.D. -- and they said go to a liberal arts school and get a good, well-rounded, traditional geological education," she says. "One of them -- he actually was a former professor at Brown -- recommended William and Mary."
She says she became a geology major "back when the department was in Small Hall" and credits her many and varied undergraduate field experiences as helping her to understand the geology of Earth as well as less hospitable places.
"We did a lot of field work going up into the Appalachians. For almost every class I took, we would be able to go to some part of Virginia, because William and Mary is in a great setting," she said in an interview following her presentation in McGlothlin-Street Hall. "If we were doing soft rock, more sedimentary rocks, we'd go out to the shoreline, the Chesapeake. We went down to the Outer Banks at one point."
Looking at a lot of terrestrial formations proved to be indispensable for a scientist who studies the methane table -- or methanifer, like Earth's aquifers -- of a remote moon and how it interacts with the numerous lakes and seas found on its surface. "Even though they're such weird materials, they're behaving like they are on Earth," she says.
If geology is odd, so are the conditions; Stofan's team gets their information in the form of long skinny strips of the moon's surface from individual passes by the Cassini radar. It takes a trained eye to decipher the features correctly.
"When we got the strips back, we said, 'We think these are lakes; we think we finally got it,'" Stofan says. "But being scientists, everyone starts saying, 'Well, what if there's this other explanation?'"
Stofan's geology experience helps her approach these issues from a unique perspective. "In the field of planetary geology, for instance, a lot of people come from a physics background. They don't have the geology background, let alone field-based experience," she says. Planetary experience is helping Stofan understand the secrets of plain old terrestrial geology as well.
"When I go out into the field and work on volcanoes, I realize that what I can see in the remote sensing data for terrestrial volcanoes really only gives you a limited view of how that volcano works," she says. "You always have to keep that in mind when you go down and look at a volcano. When you are able to go to other planets and look at volcanoes, you can put all that information together. It allows you to say: How does volcanism work as a fundamental process? It's like a doctor who only has one patient. You might have some great theories of how the human body works, but all of a sudden if you have a hundred people, you realize that gosh, maybe some of the theories were oversimplified."
Stofan doesn't always study geology from afar. In fact, she has been known to plan family vacations that just happen to be in the vicinity of active volcanoes. Even regular vacations to the beach can be interrupted by incoming radar strips from Cassini.
"Whenever you get a strip back, life stops for me," she says. While Stofan works with the Jet Propulsion Laboratory at her computer, her kids are known to ask, "Why can't Mom just hang out on the beach?" Stofan does add, however, that "they've gotten pretty used to it."
The next steps for Stofan, she says, are in two different directions. First, she is involved with a number of committees that are working toward launching an exploratory probe back to Venus, a planet she examined 15 years ago with the Magellan mission. This doesn't, however, distract her from her other goal. Ellen Stofan, the "radar geologist," is still pushing to go back to the surface of Titan, the "fuzzy orange tennis ball."
"If I had the money, we'd be putting a lander on the surface to see if we're right," she says. A scientist, after all, can never be too sure.
