Stardust's return capsule entered Earth's atmosphere at 46,660km/h
(29,000mph), the highest re-entry speed of any probe ever.

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** 99% nothing **

The successful return to Earth of NASA's Stardust capsule offers scientists a
first chance to handle cometary dust. The probe bearing it flew close to comet
Wild-2 in January 2004.

http://news.bbc.co.uk/1/hi/sci/tech/4627770.stm

One theory for the beginnings of life on Earth is that our planet was seeded by
chemicals delivered by a comet. It's a concept known as panspermia.

http://www.bbc.co.uk/science/space/life/beginnings/comet.shtml

Stardust also managed to collect rare interstellar particles on its seven-year
trip. A substance called Aerogel - which is 99.8% empty volume - was used to
collect microscopic dust without damaging it. Researchers want the help of
people the world over to examine photographs and spot traces of the particles.

http://news.bbc.co.uk/1/hi/sci/tech/4607318.stm