Soon, the jeep-size rover Curiosity will trace its first six-wheeled tracks over the Martian surface. Over the next 23 months, Curiosity will scoop dust and drill into rocks for clues to the Red Planet's past. Although those samples won't make it back to Earth, some Martian rocks are already catalogued and preserved here as part of NASA's astromaterials collection.

Astromaterials are fragments and particles from planets, asteroids, stars and other extraterrestrial bodies. Scientists gather the materials during manned and unmanned space missions or after they naturally land on Earth as meteorites.

"About one in one thousand of the meteorites that fall on Earth was actually knocked off Mars by ancient impacts," says Carlton Allen, the collection curator based at the NASA Johnson Space Center in Houston. He coordinates the efforts of more than 30 people to document, preserve and distribute the samples for researchers around the world. These samples help scientists understand the formation and development of the solar system.

The collection includes lunar rocks gathered by the Apollo astronauts, particles of cosmic dust collected by special aircraft swooping through the stratosphere, and atoms carried by the solar wind.

Chemical and physical analyses can trace rocks that end up on Earth back to their extraterrestrial sources. Scientists crush small pieces of meteorites to a fine powder and analyze how the particles bend light when suspended in oil. Or, they microscopically view thin sections of the rocks and classify their structures. Then, they compare the results with what they already know about the moon, Mars, asteroids and comets.

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The extraterrestrial samples require special laboratories and handling practices to keep their otherworldly purity. For example, during the six Apollo moon-landing missions astronauts photographed lunar rock and soil samples, packaged the materials in uniquely marked, vacuum-tight containers, and returned them to Earth in sterile conditions free from contamination by terrestrial gases. "The Apollo collection comprises some of the most carefully documented geologic material in the world," wrote Allen and colleagues in an article about NASA's extraterrestrial bounty, published in February 2011.

Another NASA mission to return extraterrestrial samples to Earth was the Genesis probe, launched in 2001. The spacecraft circled at one of the Earth–sun Lagrangian points for almost two and a half years, where the combined gravitational pull of the two bodies provides a stable position. The spacecraft's circular arrays gathered solar-wind ions streaming from the sun with wafers made of silicon, germanium and gold-on-sapphire, along with films of diamond-like carbon on silicon and other materials. Despite a crash landing in the Utah desert, which breached the spacecraft's container of over 400 samples of charged particles, some of the collected astromaterials proved pure enough for research. Genesis' data from the captured solar wind helped researchers rethink their understanding of the sun's and early solar system's composition.

Other successful sample return missions include NASA's Stardust spacecraft, which collected dust samples from Comet Wild 2 and the Japan Aerospace Exploration Agency's Hayabusa probe, which gathered asteroid samples in 2010. In the future Allen and his colleagues may preside over samples collected during planned missions to other asteroids and Mars. In addition to providing a window to other worlds and the distant past, these exotic, otherworldly artifacts are simply beautiful.