Annefrank
Key facts
- What it is
- Main-belt asteroid
- Size
- About 6 km long
- Discovered
- 1942, by Karl Reinmuth
- Spacecraft
- Stardust fly-by, 2002
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.21 au (about 330 million km)
- Time to go round the Sun
- 3.3 years
- Closest and farthest from the Sun
- 2.07 to 2.35 au
- Tilt of its orbit
- 4.3°
- Spins once every
- 15.1 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Annefrank is a small asteroid in the inner main belt, about 6 kilometres long, that played a supporting role in one of the great space missions. On 2 November 2002 NASA's Stardust spacecraft, on its way to collect dust from the comet Wild 2, flew within about 3,000 kilometres of it.
The fly-by was a rehearsal. Stardust's team used Annefrank to practise the sequence of steps the spacecraft would need for its comet encounter: finding a small, faint target, locking its camera on it and tracking it as it rushed past. The test went well, and about fourteen months later Stardust flew through the dusty halo of Wild 2 and caught comet particles that it brought back to Earth in 2006.
The images of Annefrank showed an irregular, angular body, larger than astronomers had estimated from its brightness alone, with a surface marked by craters. Its shape suggested it might be two or more pieces stuck together. It is an S-type asteroid, made of the stony material common in the inner part of the belt.
The asteroid was discovered in 1942 by the German astronomer Karl Reinmuth at Heidelberg. It was later named after Anne Frank, the Jewish girl whose diary, written while hiding from the Nazis in Amsterdam, became one of the most widely read books in the world. Anne Frank died in 1945 in the Bergen-Belsen concentration camp, aged 15.
Small fly-bys like this one add to our picture of the asteroid belt, and they show how spacecraft can do useful science even on the way to somewhere else.