Martian Rockhounds

Martian Rockhounds

The story below was the cover story
of the Nov/Dec 1999 StarDate magazine.
It appeared on pp. 16-19 of that issue.

A series of missions in the next decade may bring a few small samples of Mars to Earth. Scientists will search these samples for microscopic fossils or other evidence of life.

By Sid Perkins

In October 2008, residents of one of Earth's more remote regions - possibly those near Baker, Nevada, population 200 - could see a meteor blaze across the mid-afternoon sky.

The object will enter the atmosphere at about 7 miles per second, but air resistance will slow it to a mere 150 feet per second before it slams into the ground. In just a matter of moments a new Martian "meteorite" will have fallen to Earth.

In several ways, however, this meteorite will be decidedly unlike others traced to the Red Planet. Scientists will know when and where it will land, and they will whisk the fallen object into immediate quarantine.

Most important, this meteorite will contain pristine Martian rocks and soil collected by landers and rovers that will be sent to Mars over the next few years. Detailed study of this handful of specimens may not reveal whether there is, or ever has been, life on Mars. The samples will, however, extend basic knowledge about the mineral composition, geological history, and current climatic conditions of our nearest habitable planetary neighbor.

The Mars 13

In August 1996, a team of NASA and university scientists announced that it had found evidence of ancient microscopic life in a Martian meteorite retrieved from Antarctica in 1984.

The report stirred more excitement about life on Mars than the 1938 radio broadcast of "War of the Worlds," and it sent scientists scrambling to look at the other known Martian meteorites. The trouble is, there aren't that many - only 13, by most counts, and three of those weigh less than a half ounce each. Scientists know the meteorites are from Mars because ratios of certain elements found in bubbles of gas trapped inside the rock match the elements found in the Martian atmosphere by the Viking landers in the late 1970s.

And even though these meteorites give scientists the opportunity to perform a detailed hands-on analysis of an honest-to-goodness piece of Mars, they aren't ideal geological specimens for several reasons.

By a cosmic stroke of bad luck, all 13 are igneous rocks. This means they were once molten, and possibly even flowed across the surface of Mars as lava.

"Igneous rocks don't tell you a lot about water and life," says Allan Treiman, a Mars specialist at the Lunar and Planetary Institute in Houston, who has studied some of the meteorites. "They're not the first place that you'd look for a fossil. ... What we'd really like to do is get a look at these other types of rocks, especially sedimentary rocks deposited by water."

Another reason the Martian meteorites aren't the ideal geological specimens: No one can say where on Mars they came from. They could have been blasted from any of the planet's larger craters in the highlands or plains. They might even have come from far below the surface.

"It would be very difficult to understand Earth's geology from a random sample of 13 rocks," says Carl Agee, NASA's chief scientist for astromaterials at Johnson Space Center, especially if you didn't know know if they came from the top of a mountain or the bottom of the ocean.

"Geological context is a big thing," adds Treiman. And of course, the only way to know the geological context of a sample is to collect it yourself.

Great Expectations

Sojourner, the rover carried by Mars Pathfinder, captured the world's imagination when it scooted across an ancient Martian floodplain in the summer of 1997. The rover spun its wheels in the reddish soil, examined the ruts, then turned its attention to scientifically "sniffing" the rocks strewn around the landing site.

Expectations for future robotic envoys to Mars are even grander. The rovers will collect samples of rocks and soil for an eventual return trip to Earth.

Landing sites for the missions have not yet been selected, although the time of Martian year when the landers arrive narrows the options. To help winnow the choices even further, mission planners will use data obtained from Mars Global Surveyor, which has been orbiting the planet since September 1997, and Mars Climate Orbiter, which entered orbit this September.

NOTE: This article went to print before Mars Climate Orbiter was lost entering Mars orbit on September 23, 1999.

Scientists are especially interested in retrieving samples from the ancient highlands of Mars' southern hemisphere, an area of heavily cratered terrain that has remained relatively unchanged for the past 3 billion to 4 billion years, says Mark Adler, mission and systems manager for the Mars sample return missions at NASA's Jet Propulsion Laboratory. Images from orbit suggest that a great deal of water flowed over the highlands in the distant past.

Adler says the rover on each sample return mission will spend about 90 days exploring the area surrounding its landing site, making ever-widening loops that could extend beyond the lander's horizon. These extended kin of Sojourner won't simply pick up rocks and drop them in a bucket, however. The rovers will carry a miniature rock-coring system that can drill a hole, inspect the hole and the rock pulled from inside it with a high-magnification imager, then stash or reject the sample based on instructions from its Earthbound commanders.

Rock samples will weigh about 3 or 4 grams each, and Adler says the rover will take at least two cores from each rock that it drills into. By comparing specimens from the surface of the rock with those from the inside, geologists will evaluate the extent and effects of Martian weathering.

Each rover likely will return to its lander several times during its travels. "It is especially important to get a success sample back to the lander soon after landing," Adler explains. "It would be awful to have the rover collect a beautiful set of samples, only to fail on day 85 while it's on the way back to the lander."

Contingency plans also call for the landers to collect soil samples, perhaps using scoops similar to those used on the Viking landers, or more sophisticated systems developed by Italian engineers that could dig deeper into the Martian surface.

To Mars and Back

Landing on Mars and collecting the rock and soil cores is not even half the job. There will be two different landing sites on Mars, the two missions will take place about 26 months apart, and there's only one vehicle coming back from Mars - all of which will require intricate orbital choreography before the samples can be boosted back to Earth.

The first mission will land on Mars in December 2003. The rover will return to the lander 90 days later and load its samples -between 500 grams and 1 kilogram total (1.1 to 2.2 pounds) - into a sphere a little bigger than a softball that will be packed into the ascent craft and blasted into low Mars orbit.

In August 2005, the second mission will send a rover/lander combination and an orbital rendezvous craft, which will reach Mars the following July. While the rover and lander collect their samples, the rendezvous craft will recover the samples from the first mission, then add those from the second mission after they blast into Mars orbit in October 2006.

The Earth-return vehicle will leave Mars orbit in July 2007 and reach Earth in 2008.

NASA is still evaluating potential landing spots for the sample return craft. In any case, the craft must be directed toward sparsely populated areas because it could land anywhere within a 12- by 30-mile oval surrounding the aimpoint. Landing sites now being considered include locations within the Utah Test and Training Range - 2,675 square miles of military proving grounds that straddle Interstate 80 near the Nevada border - and the White Sands Missile Range , a sprawling complex in south central New Mexico.

Once the recovery team has swooped down upon the sample return vehicle, it will extract the sealed canisters of rocks and soil and carry them into an interim quarantine. The precautions taken during this period will serve two purposes: protect Earth and humans from potential Martian microbes, and protect the extraterrestrial rocks and soil from Earthly contamination.

"There's unlikely to be any risk involved with the Mars samples, but they'll be treated as hazardous until they're proven otherwise," says Carl Agee.

Once proven sterile, the samples will be transferred to a special storage and laboratory facility similar to the lab where samples from the Apollo lunar-landing missions are stored. Demand for the samples will be high. Even though the last specimens from the Apollo missions arrived in Houston nearly 27 years ago, the facility still hosts about 100 visiting scientists each year, and sends out more than 1,000 samples to researchers who are actively studying the Moon rocks.

Mars sample-return missions face significant challenges, including the massive dust storms that can envelop entire regions of Mars for days at a time. Some experts, however, say the most difficult hurdles for the mission could crop up here on Earth.

David C. Black, director of the Lunar and Planetary Institute, says the biggest challenge is to avoid overstating what scientists might be able to learn from hands-on analysis of a limited number of specimens from Mars.

"Clearly we need to bring back samples," Black says. "The combination of remote sensing and bringing back lunar samples is what helped us understand the Moon. But what concerns me most is expectation management - that [people] think we're going to get some samples that will clearly answer the question of whether there has ever been life on Mars. We're not bringing back a helluva lot of samples, and Mars is clearly a complicated place."