NASA refines its tactics in hunt for signs of life on Mars

By Kenneth Chang

NEW YORK TIMES NEWS SERVICE

April 13, 2005

Carnegie Mellon University

Alan Waggoner and colleagues at Carnegie Mellon have developed dyes that light up when they hook onto DNA or protein molecules. They hope the technique could someday be used to find life on Mars.

The landscape looked lifeless, but satellite images from orbit identified geological formations containing minerals that microbes sometimes like to nestle in, and scientists dispatched a small rover to look at the rocks up close.

Fluorescent dyes sprayed on the ground lit up, proclaiming the presence of proteins and DNA. The rover also detected chlorophyll, the energy-producing molecule of plants.

And so scientists discovered life in Chile's Atacama Desert.

Life there, one of the driest places on Earth, is sparse, but no one was surprised to find it. And they were not really hunting life on Earth. The exercise last summer was practice for the techniques scientists hope to use in the future on Mars, where the question of life remains intriguingly open.

"You've got to go look," said Alan S. Waggoner, director of the Molecular Biosensor and Imaging Center at Carnegie Mellon University in Pittsburgh and a participant in the NASA-sponsored project. "I'd give it a 50-50 shot that you could find it somewhere underground. But then that's a guess."

He is not alone. In an informal poll taken last month at a conference in the Netherlands, three-quarters of 250 scientists working on the European Space Agency's Mars Express mission said they believed Mars once possessed conditions hospitable to life. One-quarter believe it still does.

Planetary scientists have long thought that early in its history Mars may have been more like Earth, warm and wet, a place where life could have taken hold. Then the climate turned cold and dry and has remained so for several billion years. For many, the presumption was that Martian life, if any ever existed, died away long ago.

Over the past year, the notion that life not only arose on Mars but persists today has become more plausible with reports of methane gas floating in its atmosphere. The two most likely sources are geothermal chemical reactions or bacteria, and because ultraviolet light breaks down methane within a few centuries any detectable methane must have been put there recently.

Another possibility is that the methane comes from the remains of long dead organisms trapped underground as oil or coal-like deposits and transformed to methane by the heat of meteor impacts.

"The evidence is teasing us," said Everett K. Gibson Jr. of NASA's Johnson Space Center in Houston, a member of the research team that claimed in 1996 to have found organic molecules, bacteria-like fossils and other evidence of life in a Martian meteorite found in Antarctica.

Meanwhile, biologists have in recent years discovered life on Earth in places they would not have expected, adapted to the harshest conditions: in rocks miles underground, at the sunless bottoms of oceans, in extremely acidic waters.

Gibson said he believed there was life on early Mars and it could still be there. "Life tries to hang on," he said. "Life tries to do everything it can to survive."

Carbon-based life requires three essential ingredients – carbon, liquid water and energy – and all appear to be present on Mars. Carbon dioxide makes up most of Mars' thin atmosphere, and some Mars rocks, including the one that Gibson examined, are known to contain carbon.

Liquid water is no longer present at the surface, but it once was. NASA's Mars rover Opportunity found minerals, particularly an iron mineral known as jarosite, that require prolonged steeping in water to form. Images from spacecraft in orbit find signs that liquid water has burst onto the surface in geologically recent times.

Volcanic heat could provide the energy. The European Space Agency last month released photographs of Mars' north pole that showed signs of ash from eruptions.

At the Lunar and Planetary Science Conference outside Houston last month, Lindsey S. Link, a graduate student at the University of Colorado, presented calculations showing that even at temperatures not far above freezing, chemical reactions between water and minerals in the basaltic lavas of Martian bedrock could also generate energy for life to thrive on.

But if life exists, how to find it?

Detecting life

Of the spacecraft that have flown to Mars, only NASA's two Viking landers in the 1970s carried biology experiments, and they found no signs of life. The surface is cold, waterless, almost airless and bombarded by deadly radiation. Any surviving life would most likely have migrated underground, where dirt above provides shielding and heat below warms ice to water. Few expect that Martian evolution would have progressed beyond primitive microbes.

The challenge thus is to identify life that is microscopic, lives far underground and may not resemble life on Earth.

For their life-detection system, Waggoner and his colleagues at Carnegie Mellon developed fluorescent dyes that light up when they hook onto DNA or protein molecules. The dyes are designed to work even if Martian DNA and proteins do not quite come in the same forms as Earth ones.

For a test, they chose the Atacama Desert, a popular stand-in for Mars that stretches for 600 miles between the Pacific Ocean and the Andes Mountains. The wetter parts get half an inch of rain a year. The dry parts get nothing more than wisps of fog.

The scientists brought along a 9-foot-long, 400-pound solar-powered rover named Zoe, after the Greek word for life.

To simulate a real mission, a second team of scientists led by Nathalie A. Cabrol, a planetary geologist at the SETI Institute and NASA Ames Research Center in Mountain View, gathered in Pittsburgh. The team acted as mission control, reviewing images and data collected by Zoe and deciding what it should do next.

Zoe's operations were not completely autonomous. Waggoner and others had to follow the rover and squirt the fluorescent dyes onto the rocks when the scientists in Pittsburgh found a rock that they thought merited closer analysis.

Once the dyes soaked in, a xenon lamp on Zoe's underside flashed. If DNA, proteins or chlorophyll, which is naturally fluorescent, were present, they would glow, their presence captured by a camera and radioed back to Pittsburgh.

After Zoe finished its work, the trailing scientists collected rock and soil samples to verify its findings. In moister areas along the coast, Zoe successfully found lichens on rocks. In a drier area, it reported DNA and proteins on seemingly barren rocks. Later, scientists were able to cultivate bacteria from those rocks.

Another set of trials this fall will add dyes for carbohydrates and lipids, molecules found in the walls of cells.