April 25, 1998
Scooping Up a Chunk of Mars
Fresh samples from the Red Planet
By RON COWEN
Except for a gentle wind that whined softly through the empty houses, it was deathly silent. Bodies lay everywhere, heaped and flung across the ground in frozen surprise.
In Michael Crichton's 1969 novel The Andromeda Strain, an unmanned government spacecraft returns to Earth, contaminated by an alien organism that destroys an entire town.
NASA is striving to ensure that fact won't collide with fiction a decade from now, when a small capsule containing a canister the size of a soda can, packed with soil and rock fragments from Mars, is scheduled to parachute onto Earth.
Even if the container carries living material from the Red Planet -- a possibility scientists consider remote -- the organisms aren't likely to survive in Earth's environment. Nonetheless, researchers plan to handle the canister as gingerly as if it contained the Ebola virus.
"You must assume that what you bring back is hazardous until proven otherwise," says planetary ecologist Margaret S. Race of the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, Calif.
Race and other scientists outlined plans for gathering and retrieving Martian samples at the annual meeting of the American Association for the Advancement of Science in Philadelphia in February and at a conference on astrobiology at George Washington University in Washington, D.C., in March.
Contaminating Earth with critters from Mars is one concern, but scientists also want to make sure that any samples scooped up from the Red Planet are pristine, unsullied by stray organisms from our own planet. Dead or alive, terrestrial life could hitch a round-trip ride on the two robotic missions, now scheduled for launch in 2001 and 2003, that will be the first to gather and cache material from Mars. If organic compounds from Earth found their way into a storage canister, they could confound analysis of the samples.
"You have to be extremely careful not to carry along your own evidence of life," says Doug Blanchard of NASA's Johnson Space Center in Houston. In other words, you don't want to send a craft to Mars, only to discover life from New Jersey.
Arguments over the origins of amino acids and other organic compounds in the famous Martian meteorite ALH84001 highlight the problems faced in analyzing fresh samples from Mars, notes Michael H. Carr of the U.S. Geological Survey in Menlo Park, Calif. "So much of the debate about ALH84001 has been about what's terrestrial -- what has come from the ice in Antarctica -- and what is intrinsically Martian," says Carr (SN: 1/24/98, p. 54). Planetary scientists want to avoid a repeat of these arguments when spacecraft bring back samples from Mars.
To minimize such debate, engineers and scientists are contemplating several ways of sterilizing the rovers on the 2001 and 2003 missions. Crude, but highly effective methods of sterilization were once applied to entire craft traveling to Mars. Before their launch in 1976, every component of the twin Viking missions was heated to temperatures above the boiling point of water. Then each craft was baked in a giant oven for 36 hours. "The sensitive electronic equipment we have now could never withstand that kind of heat sterilization," says Race.
Instead, each rover may be suffused with hydrogen peroxide gas before launch. A powerful oxidizer, the gas kills living material clinging to the vehicle and degrades biological molecules and membranes. After the peroxide bath, the rover might be sheathed in a protective skin, or bioshield, that it would shed only after landing on the Red Planet.
To ensure that the craft is sterile, biologists will take swabs of different parts of the craft and let any cells propagate into colonies in a laboratory. In addition, they will search for signs of individual microbes or fragments of microbes that might not grow in culture, says microbiologist Roger Kern of NASA's Jet Propulsion Laboratory in Pasadena, Calif. He notes that such testing will need to take place before the launch of the Mars-bound mission, as well as after its return.
To gain a better assessment of earthly contamination, scientists may install small slides, known as witness plates, on various components of the craft, including the canister that will hold the Martian samples. After the craft returns to Earth, scientists will compare the material accumulated on those plates with the composition of the samples, as well as any matter deposited on a set of archived plates that never left Earth.
"This should give plenty of control to determine whether biological entities are the real Martian enchilada or merely contaminants that originated on Earth," says Race.
By the time the Mars-bound slides return to Earth, instruments for detecting compounds will undoubtedly be more sensitive, and standards for contamination may be more stringent.
"The techniques for detecting proteins and little pieces of DNA and so on are just unbelievable compared to what they were 5 years ago," says Carr. "Surely there is going to be a similar evolution over the next decade or so. This presents a challenge for us: The sample won't be back on Earth until 2008, so how do we make a set of requirements in the face of this rapidly changing capability?"
The first expedition takes off in 2001. It will feature a vehicle five times the size of tiny Sojourner, the six-wheeled rover on Mars Pathfinder that became a staple on the nightly news last July. Roaming a few tens of kilometers from its mother ship -- Sojourner traveled only a few meters -- the rover will use a pencil-thin drill to dig a centimeter or so into a selection of boulders lying on the Martian surface.
After analyzing the composition of each sample, the rover will transfer the nugget to a tiny treasure chest -- a box with enough cubbyholes to hold 91 samples of rock and 13 of soil, amounting to about half a kilogram of material. Two years later, according to current plans, the 2003 rover will fill a similar treasure chest on another part of the Red Planet.
In 2007, another lander and rover will arrive to pick up the booty. In a set of carefully choreographed moves, the new rover will retrieve one of the two boxes -- from whichever site seems have a more intriguing set of samples -- and deposit it in the lander. In the current strategy, the lander will blast off from the planet but will not return to Earth. To break the chain of possible contamination, the lander will rendezvous with a waiting craft, in orbit about Mars, that had never touched the surface. The lander will hand over its precious cargo, and the orbiting craft will begin its journey back to Earth.
While the samples are in transit, scientists hope to maintain them at chilly temperatures and low pressures similar to those on Mars. The canister will also be carefully monitored: A drop in pressure inside the container may indicate that Martian material is leaking out. Under such circumstances, ground controllers will redirect the craft so that it whizzes past Earth instead of landing.
If monitoring reveals no problems, however, the canister will break loose from its return vehicle as it nears Earth and parachute onto solid ground. A team of scientists -- it's not yet known whether the initial handlers will be from NASA, the Centers for Disease Control and Prevention, the military, or some other group -- will transport the canister to a designated research facility.
In a report issued last year, the National Research Council recommended that the facility be up and running for several years before the Martian cargo arrives. "It's not just a matter of it being a check-out stand at the supermarket," says John D. Rummel, planetary protection officer for NASA. "We need to be ready to deal with whatever cards we're dealt."
Because the samples will be tiny, they may be best analyzed inside a small, closed compartment known as a biosafety cabinet, or glove box, says Race. Researchers manipulate material by inserting their hands into gloves that are sealed tightly to the compartment.
"The Centers for Disease Control and Prevention has a great deal of experience in dealing with known pathogens," says Kern. "We just have to make sure that NASA follows those procedures and has experience in that."
"There's nothing about what we know on Mars so far that would lead us to believe that we're going to find anything weird," says Race. "We are not finding anything physical or chemical that is different than on Earth."
She adds, however, that the search for life in the Martian samples won't be restricted to seeking familiar molecules like DNA. On Earth, she notes, living materials "are little bags of chemical reactions that require a vessel" such as a membrane or a cell wall. Finding some similar sort of structure would be one indicator of life in the Martian samples.
"They'll slice and dice and chop it up and look at it in all different ways," says Race. Even if they find nothing, they still plan to see if the Martian material affects cells growing in the laboratory.
"We had better go the most cautious route, even though there's not a lot of people around who think we'll find little green men inside when we open the canister."
"There's always the potential that you'll find there's life on Mars but that it's so wimpy that it gets eaten by anything that runs into it," says Rummel. It would be difficult to detect organisms that are destroyed by common microbes or chemicals native to Earth.
Visions of some malevolent alien organism, like the rubber-eating microbe in The Andromeda Strain, are "not something I'm going to be losing any sleep over," says Kern.
From Science News, Vol. 153, No. 17, April 25, 1998, p. 265.
Copyright Ó 1998 by Science Service.
Race, M.S. 1998. Mars sample return and planetary protection in a public context. Meeting of the American Association for the Advancement of Science. Philadelphia.
Rummel, J.D. 1998. Planning for Mars sample return missions: Scientific, technical, and social challenges. Meeting of the American Association for the Advancement of Science. Philadelphia.
Cowen, R. 1998. Reports raise questions about Martian rock. Science News 153(Jan. 24):54.
National Aeronautics and Space Administration
Lyndon B. Johnson Space Center
Houston, TX 77058
U.S. Geological Survey
345 Middlefield Road
Menlo Park, CA 94025
California Institute of Technology
NASA Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
Margaret S. Race
2043 Landings Drive
Mountain View, CA 94043
John D. Rummel
Marine Biological Laboratory
7 MBL Street
Woods Hole, MA 02543
J. William Schopf
University of California, Los Angeles
Department of Earth and Space Sciences
Los Angeles, CA 90095-1562