R band light curve of 288P/2006 VW139

Through model analysis we separated this light curve into components, one for each fragment. We found their sidereal rotation periods and the most probable shapes and sizes. We analysed the angular momentum and energy balances and compared actual values with that expected at the moment of rotational splitting to check how much surplus has been introduced into the system.

We determined the rotation periods of the components to be 15.86 hours for the larger object A and 3.37 hour for the smaller fragment B. Assuming a geometric albedo of 0.07 in the R photometric band, surface and reflectance properties adequate for C-type asteroids and comets, and considering A and B as prolate spheroids, we found that their semi-axes a, b (where b<a) equal to 1.12, 0.69 and 0.67, 0.57km for the larger and smaller components, respectively.

The existence of a third body in 288P cannot be definitely excluded but should be considered as unlikely. A plausible mechanism responsible for the origin of the binary asteroid 288P is rotational fission of a bilobate progenitor spun up by the Yarkovsky- O'Keefe-Radzievskii-Paddack mechanism or, more likely, by sublimation-driven torque produced by an active region or regions. It is almost certain that the sublimative activity of the smaller fragment B is behind its relatively fast, completely asynchronous rotation and the wide mutual orbit of the components.