“The question I’m interested in is, ‘Is there, orwas there, life on other planets?’” says ChrisMcKay. A planetary scientist with the NationalAeronautics and Space Administration, Dr.McKay is an astrobiologist: he studies the originand distribution of life in the universe. He was afirst-year graduate student when the Vikingspacecraft landed on Mars in 1976, and “thatdid it,” he recalls. “The Viking results seemed tosuggest that the elements needed for life werepresent 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 riverchannels on Mars, suggesting that liquid wateronce flowed on the surface of a much warmerplanet. “The most interesting thing we’velearned from all the missions to Mars, beginningwith Mariner 6 in 1969, is that the planet had

an early Earth-like period,” explains McKay. “It had water, it had active volcanism, and webelieve it had a thicker atmosphere which wouldhave kept the surface warmer. These dryriverbeds lie in cratered terrain more than 3.5billion years old. Fossil remains show thatmicrobial life on Earth existed at that time.”

“Those Viking images from orbit are thedecisive information,” he says. They establishedthe framework into which information from othersources fit. “I don’t think we could havedetermined that early Mars was more Earth-likethan today from meteorites directly,” he says.“And I don’t think anyone would have taken themeteorites seriously if we hadn’t had thepictures. All that hullabaloo about finding life” (in1996 scientists discovered that Martianmeteorite ALH84001 contains tiny, egg-shapedstructures which possibly constitute evidence of

Looking for Life in Antarctica… and on Mars

Chris McKay on the ice of an Antarctic lake.

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fossilized bacteria) “makes sense because ofwhat we already knew.”

“As planets go, Earth and Mars are still verysimilar bodies, although their evolutionaryhistories diverged several billion years ago,”wrote McKay and co-authors E. Imre Friedmannand Michael Meyer in an article in The PlanetaryReport titled “From Siberia to Mars.” “Geologicalprocesses seem to have obliterated evidence oflife on Earth before 3.5 billion years ago; atleast we haven’t found any yet. But two-thirds ofthe Martian surface dates back further thanthat, so Mars may actually hold the best recordof the events leading to the origin of life onMars and on Earth, even if there is no life there today.”

McKay’s research takes place in the harshestclimates on Earth, “because Mars is dry andcold,” he explains cheerfully. The dry valleys ofAntarctica are a prime destination because, withless than an inch of precipitation a year and anaverage temperature of -20°, they are the mostMars-like places on Earth. There, on windsweptmountain slopes, tiny life forms—algae, lichens,bacteria—grow in the rocks. These microscopicorganisms are called cryptoendoliths (from theGreek, crypto=hidden, endo=in, lith=rock). IfMars ever had life, biologists reason, its lastsurvivors might have resembled these cryptoendoliths. And similar environments onMars could have provided a refuge long afterconditions 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 torecord basic environmental information: temperature light, humidity, wind.” To monitorconditions within the rock, he drills little holes into which he inserts tiny moisture andtemperature sensors that hook up to the data logger. The other invaluable tool is the

microscope: “a portable one that I take into thefield, plus a low-power hand lens, for looking atthe organisms that live in these environments.”McKay and his colleagues monitor a number ofsites around the world, maintaining them forseveral years and sometimes longer. “Forexample, after four years in the Atacama desertin Chile, we still haven’t seen any rain. We’rewaiting to see how long it takes.”

Scientists also extract core samples from siteswhere life forms could have been preserved bythe freezing temperatures. Seventy-five feet intothe Siberian permafrost, they’ve found largenumbers of 3.5 million-year-old-bacteria, whichappear unharmed when thawed. Astrobiologistslike Chris McKay hope that conditions at Mars’sSouth Pole, parts of which have remainedfrozen at temperatures of -70°C since thecreation of the planet, might have preservedsimilar tiny life forms. Any such organismswould have been killed by background radiationfrom ever-present radioactive elements in theMartian soil. However, the extreme cold wouldbe ideal for preserving their intact bodies, whichscientists could then subject to chemical andgenetic analysis.

McKay’s next trip will probably be back to theAtacama or to his station in Antarctica. But he’skeeping a sharp eye on outer space, sinceNASA uses information from him and otherastrobiologists to decide where else in the solarsystem to search for life. “Of particular interestto me in terms of biology is Europa, one ofJupiter’s moons. We think that underneath theice there’s an ocean,” he explains. “We havemissions going to many of the planets, thoughmore to Mars than all others put together.”McKay thinks that the optimum destinationwould be the bottoms of dried Martian lakes.“These represent a place where life could havesurvived long after life outside the lake wasdead, just as we see in dry valleys of

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C A S E S T U D Y : L I F E I N A N T A R C T I C A

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’reeasily identifiable, ancient lakebeds also make a practical target—and a nice flat landingspace—for a spacecraft. Nevertheless the technical obstacles—“getting to Mars, muchless landing there”—are daunting. “It’s a longway,” admits the astrobiologist.

McKay thinks the current program of roboticexploration will eventually lead up to humanexploration of Mars, “maybe in the first coupleof decades of the next century.” Landing in thepermafrost of Mars’s southern region anddrilling down deep in this colder, less sunnyenvironment would be even more difficult than

a touchdown on a Martian lakebed. But that’swhere the best chance exists of recoveringactual organisms, dead or alive. “Distinguishingwhether any such life forms are built of thesame building blocks as life on Earth would berelatively easy,” says McKay. “Now we can doPolymerase Chain Reaction, geneticsequencing, with exquisite accuracy. If it lookslike us, that will be clear. But if it looks like abunch of strange biomolecules forming thebody of an alien microbe, we will have a hardtime understanding how its biochemistryworked. I’d love to have that challenge.”

A ventifact, a wind-carved rock, from Antarctica.

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