On November 2, 2002, the Stardust space probe flew past Annefrank at a distance of 3079 km. Its images show the asteroid to be 6.6 × 5.0 × 3.4 km, twice as big as previously thought, shaped like a triangular prism, with several visible impact craters. From the photographs, the albedo of Annefrank was computed to be between 0.18 and 0.24. Preliminary analysis of the Stardust imagery suggests that Annefrank may be a contact binary, although other possible explanations exist for its observed shape.
Later ground based lightcurve data was used in an attempt to measure Annefrank's rotational period. Their data resulted in possible rotational periods of 0.5, 0.63 or 0.95 days, with 0.63 days fitting the data best. The lightcurve data also suggests that the asteroid is not Lambertian, meaning that surface features, such as shadows from boulders and craters, play a role in the object's perceived brightness and not just the asteroid's relative size when seen from that orientation.
^ abSchmidt, B. E.; Bauer, J.; Buratti, B. J.; Russell, C. T. (March 12–16, 2007). "Rotational Light Curve and Rotation Period of 5535 Annefrank". 38th Lunar and Planetary Science Conference: 1859. Bibcode:2007LPI....38.1859S.