Stardust spacecraft at Comet Wild-2, computer artwork. Stardust passed through the gas and dust cloud (coma) of Comet Wild-2 on 2 January 2004. It collected dust samples to be returned to Earth. It passed by the comet at a speed of six kilometres a second, just beyond the orbit of Mars. The sample collector, made of aerogel, has been deployed here (round, blue). Shields protected the rest of the spacecraft, including two bumper shields (black) at the front of the solar panels (blue). Stardust, launched in 1999, took 5 years to reach Comet Wild-2. It will return to Earth in January 2006. Cometary dust is studied because it is a sample of material from the formation of the solar system.