SHARON SHANKS | The Cosmos Reaching out to touch stars and planets

We're a tactile species. From our first moments outside of the womb, we're touching and feeling. A newborn baby is quieted by a mother's caress; a small child touches and probes every new thing within reach. Once we're older, we take things apart and douse things with chemicals to see how they work and react.
Imagine how frustrating it is, then, for astronomers. Except for a few chance meteorites, astronomers can't touch what they're studying. They're limited to looking (and, with only one or two instruments, to listening). This handicap has led to the development of marvelous tools for studying the stars at a distance, but despite the abilities of spectrometers, the Hubble Space Telescope, interferometers and other instruments, astronomers would give anything to get their hands on a piece of the cosmos.
One mission already in progress and two missions planned in the next several years will do just that: bring back samples.
Tailing a comet: Stardust was launched in February 1999. Its mission: to bring back dust, specifically interstellar material and the debris from a comet's tail. The mission is a long one. It has already scooped up (hopefully) samples of interstellar dust when its collectors were opened in the spring of 2000, and it will try again in the summer and fall of 2002.
In January 2004 it will fly past and through the tail of Comet Wild-2 (pronounced "vilt") and then head for home with its collectors stowed inside a clam-shaped capsule. If all goes as designed, the capsule will land in the Utah desert in January 2006.
Comet Wild-2 was selected because it would be in the right place at the right time for the mission, and it's a relatively "new" comet that hasn't shed much of its dust and gases in repeated trips around the sun.
The Stardust collectors are made of aerogel, a unique silicon-based material that's 99.8 percent air and a thousand times less dense than glass. Aerogel is light enough to trap tiny particles less than a thousandth of a millimeter across and still allow them to be found in the collection material.
Origins: Another collection mission is being prepared for launch this summer. It's called Genesis, and as its name implies, it will be looking for clues to our very beginnings: the formation of the solar system itself.
The most probable theory explaining the formation of our little neighborhood in space says that our sun and planets formed from an immense cloud of gas and dust. The cloud, the leftovers from earlier generations of exploded stars, began rotating and collapsed under the influence of gravity. When enough material gathered together, our sun was born; the rest of the inhabitants of the solar system (the planets, moons, asteroids and comets) formed from the leftovers.
The question, however, is how did this material that formed the sun also form such a diverse array of objects? We have Venus, a rocky planet with a poisonous atmosphere; Jupiter, a giant made mostly of gases; and Earth, our hospitable abode.
Scientists know a lot about the solar system from long-range observations of the sun and planets and lander and probe missions, but they don't know what the original solar nebula was made of. The best place to find this answer is from the atmosphere of the sun, and Genesis' goal is to collect this material.
We can't get close enough to the sun to collect directly from its atmosphere, of course, so the spacecraft will collect the next best thing: particles escaping the sun in the solar wind.
Genesis will be equipped with a different sort of collection material: thin, highly purified wafers of a variety of materials. Its path will take it to a spot between the Earth and sun where the gravity of the two bodies is balanced. These spots are called the Lagrangian points, and Genesis will be posted at L1 (Lagrangian point 1).
It will collect the extremely tiny and rare particles for two years before heading back to Earth, where it will be snagged in mid-fall by a helicopter over Utah. It is due back in September 2004, beating Stardust back to Earth by two years.
Mars: Then, of course, there's Mars. A sample return mission has been on the drawing boards for decades, but the date of the mission keeps getting pushed further into the future as NASA works on consistently successful landings on Mars. The Mars Pathfinder mission was a great success in 1997, but the Mars Polar Lander and the Mars Climate Orbiter were both lost in 1999.
Plans right now call for the first sample return mission in 2014 and a second in 2016. If technology and the success rate cooperate, the timeline could be pushed to 2011.
Scientists do have samples of Mars now -- meteorites blasted off the surface of our neighbor planet millennia ago that were captured by Earth's gravity and landed here. But the meteorites just aren't enough -- they've been contaminated by exposure while lying for hundreds of centuries on Earth's surface.
Contamination is one of the major and most compelling arguments against the possibility of fossilized microbes from Mars trapped within ALH84001, the now very famous Martian meteorite studied extensively by scientists. The only way to be sure that our samples of Mars haven't been contaminated is to collect them directly from the Martian surface.
Of course, if we find no sign of ancient life in samples from Mars, it may just mean we've collected the wrong rocks. To answer this question will take a human mission to Mars -- the ultimate tactile experience.

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