Looking For Life In Antarctica..and on Mars
“The question I’m interested in is, ‘Is there, or was there, life on other planets?’” says Chris McKay. A planetary scientist with the National Aeronautics and Space Administration, Dr. McKay is an astrobiologist: he studies the origin and distribution of life in the universe. He was a first-year graduate student when the Viking spacecraft landed on Mars in 1976, and “that did it,” he recalls. “The Viking results seemed to suggest that the elements needed for life were present on Mars but there was no life there. That puzzle, that paradox, is what got me interested in the whole thing.”
Satellite images show what might be long river channels on Mars, suggesting that liquid water once flowed on the surface of a much warmer planet. “The most interesting thing we’ve learned from all the missions to Mars, beginning with Mariner 6 in 1969, is that the planet had an early Earth-like period,” explains McKay. “It had water, it had active volcanism, and we believe it had a thicker atmosphere which would have kept the surface warmer. These dry riverbeds lie in cratered terrain more than 3.5 billion years old. Fossil remains show that microbial life on Earth existed at that time.”
“Those Viking images from orbit are the decisive information,” he says. They established the framework into which information from other sources fit. “I don’t think we could have determined that early Mars was more Earth-like than today from meteorites directly,” he says. “And I don’t think anyone would have taken the meteorites seriously if we hadn’t had the pictures. All that hullabaloo about finding life” (in 1996 scientists discovered that Martian meteorite ALH84001 contains tiny, egg-shaped structures which possibly constitute evidence of fossilized bacteria) “makes sense because of what we already knew.”
“As planets go, Earth and Mars are still very similar bodies, although their evolutionary histories diverged several billion years ago,” wrote McKay and co-authors E. Imre Friedmann and Michael Meyer in an article in The Planetary Report titled “From Siberia to Mars.” “Geological processes seem to have obliterated evidence of life on Earth before 3.5 billion years ago; at least we haven’t found any yet. But two-thirds of the Martian surface dates back further than that, so Mars may actually hold the best record of the events leading to the origin of life on Mars and on Earth, even if there is no life there today.”
McKay’s research takes place in the harshest climates on Earth, “because Mars is dry and cold,” he explains cheerfully. The dry valleys of Antarctica are a prime destination because, with less than an inch of precipitation a year and an average temperature of -20°, they are the most Mars-like places on Earth. There, on windswept mountain slopes, tiny life forms—algae, lichens, bacteria—grow in the rocks. These microscopic organisms are called cryptoendoliths (from the Greek, crypto=hidden, endo=in, lith=rock). If Mars ever had life, biologists reason, its last survivors might have resembled these cryptoendoliths. And similar environments on Mars could have provided a refuge long after conditions on the surface became too cold and dry to support life.
The astrobiologist’s main tool is a data logger, “a little computer that I leave out all year long to record basic environmental information: temperature light, humidity, wind.” To monitor conditions within the rock, he drills little holes into which he inserts tiny moisture and temperature sensors that hook up to the data logger. The other invaluable tool is the microscope: “a portable one that I take into the field, plus a low-power hand lens, for looking at the organisms that live in these environments.” McKay and his colleagues monitor a number of sites around the world, maintaining them for several years and sometimes longer. “For example, after four years in the Atacama desert in Chile, we still haven’t seen any rain. We’re waiting to see how long it takes.”
Scientists also extract core samples from sites where life forms could have been preserved by the freezing temperatures. Seventy-five feet into the Siberian permafrost, they’ve found large numbers of 3.5 million-year-old-bacteria, which appear unharmed when thawed. Astrobiologists like Chris McKay hope that conditions at Mars’s South Pole, parts of which have remained frozen at temperatures of -70°C since the creation of the planet, might have preserved similar tiny life forms. Any such organisms would have been killed by background radiation from ever-present radioactive elements in the Martian soil. However, the extreme cold would be ideal for preserving their intact bodies, which scientists could then subject to chemical and genetic analysis.
McKay’s next trip will probably be back to the Atacama or to his station in Antarctica. But he’s keeping a sharp eye on outer space, since NASA uses information from him and other astrobiologists to decide where else in the solar system to search for life. “Of particular interest to me in terms of biology is Europa, one of Jupiter’s moons. We think that underneath the ice there’s an ocean,” he explains. “We have missions going to many of the planets, though more to Mars than all others put together.” McKay thinks that the optimum destination would be the bottoms of dried Martian lakes. “These represent a place where life could have survived long after life outside the lake was dead, just as we see in dry valleys of Antarctica,” he points out. “They’re also a good place for fossil remains, because they settle in calm lake bottoms. That’s a big advantage over a riverbed.” Because they’re easily identifiable, ancient lakebeds also make a practical target—and a nice flat landing space—for a spacecraft. Nevertheless the technical obstacles—“getting to Mars, much less landing there”—are daunting. “It’s a long way,” admits the astrobiologist.
McKay thinks the current program of robotic exploration will eventually lead up to human exploration of Mars, “maybe in the first couple of decades of the next century.” Landing in the permafrost of Mars’s southern region and drilling down deep in this colder, less sunny environment would be even more difficult than a touchdown on a Martian lakebed. But that’s where the best chance exists of recovering actual organisms, dead or alive. “Distinguishing whether any such life forms are built of the same building blocks as life on Earth would be relatively easy,” says McKay. “Now we can do Polymerase Chain Reaction, genetic sequencing, with exquisite accuracy. If it looks like us, that will be clear. But if it looks like a bunch of strange biomolecules forming the body of an alien microbe, we will have a hard time understanding how its biochemistry worked. I’d love to have that challenge.”
More About This Resource...
Less than 1 period
Supplement a study of geology or astronomy with an activity drawn from this essay about the search for life in Antarctica and on Mars.
- Ask students to speculate about what scientists can learn about Mars from studying Antarctica.
- Send students to this online article, or print copies of the essay for them to read.
- Have them write a one-page reaction to the article, explaining what they learned about McKay's work in the dry valleys of Antarctica.
SubtopicHistory of Earth and Planetary Sciences