5535 Annefrank

5535 Annefrank is a small, stony asteroid in the inner part of the main belt, and it owes its place in space history to a rehearsal. On 2 November 2002, NASA’s Stardust spacecraft swept past it at a distance of about 3,079 kilometres — not because Annefrank was the mission’s goal, but as a practice run to test the probe’s cameras and tracking before its real target, comet Wild 2. The flyby returned the first close-up images of the asteroid, and they held a surprise: Annefrank turned out to be roughly twice as large as ground-based observations had suggested.

Annefrank is an S-type asteroid — a body of silicate rock — and a member of the Flora family, a cluster of fragments in the inner belt. It measures about 6.6 kilometres along its longest axis, with an irregular, roughly triangular, prism-like outline pitted with craters. Its lopsided shape has even led some researchers to suspect it may be a contact binary, two smaller bodies fused together, though the evidence is not conclusive.

Discovered in 1942 by Karl Wilhelm Reinmuth at Heidelberg and later named in memory of Anne Frank, the asteroid is a quiet member of the asteroid belt that briefly became a proving ground. By testing its instruments on Annefrank first, Stardust went on to fly through the coma of Wild 2 and carry the first cometary dust home to Earth.