Annefrank is a member of the Flora family, one of the largest collisional populations of stony asteroids in the main-belt. It orbits the Sun in the inner main-belt at a distance of 2.1–2.4 AU once every 3 years and 3 months (1,202 days). Its orbit has an eccentricity of 0.06 and an inclination of 4° with respect to the ecliptic.[1]
The body's observation arc begins at Crimea–Nauchnij in 1978, with its identification as 1978 EK6, 36 years after its official discovery observation at Heidelberg.[11]
On 2 November 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, and its main body shaped like a triangular prism with several visible impact craters.[8] From the photographs, the albedo of Annefrank was computed to be between 0.18 and 0.24.[8] Preliminary analysis of the Stardust imagery suggests that Annefrank may be a contact binary, although other possible explanations exist for its observed shape.[8]
Rotation and poles
In October 2006, ground-based photometric observations were used in an attempt to measure Annefrank's rotational period. Analysis of the ambiguous lightcurve gave a period of 15.12 hours and a brightness variation of 0.25 magnitude with two alternative period solutions of 12 and 22.8 hours, respectively (U=2).[3][5]
In January 2014, photometric observations at the Palomar Transient Factory gave a rotation period of 15.156 and 21.33 hours with an amplitude of 0.17 and 0.20 magnitude, respectively (U=2/2).[6][7]
The lightcurve data suggests that Annefrank 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.[5]
The body's shortest axis is approximately aligned perpendicular to its orbital plane.[8]
