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In Antarctica, CAS prof sees Mars

By Tim Stoddard

If Commonwealth Avenue feels like the coldest, windiest place on earth this week, consider the Antarctic landscape where David Marchant and three BU students recently pitched camp for three months. Marchant, a CAS associate professor of earth sciences, has returned to Antarctica every austral summer for the last 17 years to study the unique geologic record of the Dry Valleys. While 98 percent of Antarctica is covered by a vast, featureless ice sheet, the Dry Valleys are mostly ice-free. By studying the geological record of the rocks and sediments there, Marchant has been shedding light on how earth’s climate has changed through the ages. But now his work is also kindling excitement among planetary scientists exploring the even drier and colder landscape of Mars.

David Marchant and several BU undergraduates faced the challenges of fieldwork in Antarctica last semester. Marchant has endured extreme conditions at the bottom of the world to understand how earth’s climate has changed through the ages. Now his expertise may help NASA scientists find ice and water in the even colder, drier Martian landscape. Photo by Adam Lewis

NASA scientists have long considered the Dry Valleys of Antarctica to be the most Mars-like environment on earth. But in the past few months, Marchant and colleague James Head, a planetary scientist at Brown University, have discovered a link between Mars and Antarctica that’s opening the door to a new way of exploring and understanding the red planet.

Martian prospecting
One of the hottest topics in planetary science is the presence of water on Mars, because where there’s water, there may be evidence of past or present life. Mars has ice at both poles, but NASA scientists believe there may be buried ice in various other regions as well. Finding this buried ice has become a priority of NASA’s Mars Exploration Program, and Marchant’s expertise in understanding how ice has shaped the Dry Valleys is drawing international attention.

Up until last October, however, Mars was not even on Marchant’s radar screen. His primary interest in the Dry Valleys has been the East Antarctic Ice Sheet, and the controversial question of whether it melted and collapsed during the Pliocene period four million years ago. Marchant’s research shows that the ice sheet remained intact throughout the Pliocene period, which means that if present global warming trends continue in the near future, it is not likely that the ice sheet will melt and cause sea levels to rise.
When Head invited Marchant to give a lecture at Brown about this last October, he made an important connection. “Dave gave this incredible talk,” Head says, “and while he was going through his slides, I had an epiphany. I realized that I had seen the exact same features that he was describing in the Dry Valleys in photos taken of Mars.”

Several weeks later, Head visited Marchant at BU and brought him photographs from NASA’s Mars Global Surveyor satellite. Without telling Marchant what he was looking at, Head asked him to interpret the images. Marchant immediately identified what looked like ridges and contours left by so-called cold-based glaciers in the Dry Valleys.

The glaciers most of us are familiar with are wet-based, meaning that some of their ice melts and the water trickles down to their base and lubricates the interface between ice and substrate. This allows wet glaciers to flow across a landscape, carving out telltale marks in their wake. But in places where it’s too cold for ice to melt, such as in Antarctica, the glaciers deform internally, moving without sliding on the landscape, “much like a slug sliding over sand grains,” Marchant says. When cold-based glaciers advance and retreat, they don’t leave scour marks, channels, drumlins, or all the glacial features that we see around us in New England. They leave only faint lines of rocks, called drop moraines, and other subtle clues.

“We’ve seen features like this on Mars for years,” Head says. “But there’s been debate over what they were and how they were formed. They resemble glacial marks, but you don’t see all those features that are indicative of most glaciers.” The problem before, he adds, is that most planetary scientists weren’t familiar with cold-based glaciers. But for Marchant, the Martian features were obviously similar to those in the Dry Valleys.

	David Marchant’s research in the Dry Valleys of Antarctica suggests that sea levels will probably not rise dramatically if global warming continues. In the early 1990s, he discovered buried ice in the Dry Valleys that is at least 8.1 million years old. Bubbles of ancient air trapped within that ice may be the only record of the earth’s atmosphere in the Pliocene period. Photo by Adam Lewis

Last week, Head presented new research he had conducted with Marchant at a planetary science meeting in Spain. The work suggests that fan-shaped deposits on Arsia Mons, a volcano near Mars’ equator, were left by a cold-based glacier. This is significant because it means that ice was probably deposited there at a time when Mars was tilted differently towards the sun, which supports a theory that the planet’s orientation has varied significantly over time. It also means that there may be buried ice at many latitudes on the planet.

“We can use surface textures from the Dry Valleys to map buried ice on Mars,” Marchant says. “Jim and I have basically found a new way to look at Martian landforms. It seems to really explain atmospheric circulation on Mars, and the presence and distribution of what we think is buried ice, and the movement of that ice.”

Marchant’s work, which will be featured in several international publications later this month, is of keen interest to scientists planning to send a pair of 400-pound robotics to Mars in January 2004. If all goes well, these rovers will uncover new clues about how water shapes Martian landscapes, soils, and ice caps. The critical step will be interpreting that data with a physical model such as Antarctica’s Dry Valleys.

“All of us in the NASA Mars Exploration Program are excited about the work that Professor Marchant and his colleagues are doing in Antarctica, and we believe it will have a real impact on how we interpret data from the upcoming mission,” says Jim Garvin, the lead scientist for NASA’s Mars Exploration Program. “Marchant’s work may serve as a catalyst for a fresh look at how Martian landscapes at many scales have formed, and it may also help us plan terrestrial field experiments to Antarctica and other dry, cold locales to determine what will be the best diagnostic features to measure.”

24 January 2003
Boston University
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