On January 15, 2006, a capsule hit Earth’s atmosphere at 12.9 kilometers per second, the fastest reentry of any human-made object, protected by an ablative heat shield that burned away at over 2,900 degrees Celsius. Inside was about one milligram of comet dust. This episode explores NASA’s Stardust mission, born from the Discovery Program after the cancellation of the Comet Rendezvous Asteroid Flyby, and its target Comet Wild 2, which Jupiter flung into the inner solar system in 1974 with its primordial material still pristine.

We explain how aerogel, a silica solid that is 99.8 percent empty space, captured hypervelocity grains without vaporizing them, how Whipple shields turned incoming debris into harmless gas, and why a 450 meters-per-second impact shock sterilized any microbes. We follow the 1999 launch, the Earth gravity assist, the Annefrank rehearsal, the January 2004 encounter at 6.1 kilometers per second guided by AutoNav, and the Stardust@home volunteers who scanned a million images. The results included high-temperature olivine and pyroxene in a cold comet, minerals formed in liquid water, and in 2009 the amino acid glycine, before the spacecraft’s NExT extension to Tempel 1 and a final burn to empty in 2011.

• How an ablator shield carries heat away by turning solid into gas
• Why catching comet dust is like stopping a bullet with a butterfly net, and how aerogel does it
• How mass spectrometry reads a single milligram atom by atom
• What crystalline silicates and glycine in Wild 2 imply about a mixing early solar system and the origins of life
• Why a microchip carrying a million names is still orbiting the sun