A Model for Rotation and Shape of Asteroid 9969 Braille from Ground-Based Observations and Images Obtained during the Deep Space 1 (DS1) Flyby

Abstract

Image data from the DS1 encounter with Asteroid 9969 Braille and data from a coordinated ground-based photometric observing campaign are combined to study the physical properties of this small Mars crosser. From telescope data the object's brightness was found to vary by up to 0.5 mag from night to night, with the most probable synodic rotational period being 226.4±1.3 h (9.4 days) and a mean lightcurve magnitude R(1, α=24°) =17.04±0.10. During the flyby of the spacecraft, two frame images from a range of approximately 13,500 km and phase angle 82.4°, which impose strong constraints on size, shape, and albedo of the object, were obtained. Using telescope and flyby data in combination, the asteroid is estimated to have a size of 2.1×1×1 km 3 and shown to have photometric properties similar to the asteroid 4 Vesta, notably a comparably high albedo. The high albedo supports the notion (L. Soderblom et al. 1999, Bull. Am. Astron. Soc. 31,) that Braille is of the V or Q taxonomic type.