Towards understanding the β Pictoris dust stream

The recent radar detection by Baggaley (2000) of a collimated stream of interstellar meteoroids postulated to be sourced at β Pictoris, a nearby star with a prominent dust disk, presents a challenge to theoreticians. Two mechanisms of possible dust ejection from β Pic have been proposed: ejection of dust by radiation pressure from comets in eccentric orbits and by gravity of a hypothetical planet in the disk. Here we re-examine observational data and reconsider theoretical scenarios, substantiating them with detailed modeling to test whether they can explain quantitatively and simultaneously the masses, speeds, and fluxes. Our analysis of the stream geometry and kinematics confirms that β Pic is the most likely source of the stream and suggests that an intensive dust ejection phase took place ∼0.7 Myr ago. Our dynamical simulations show that high ejection speeds retrieved from the observations can be explained by both planetary ejection and radiation pressure mechanisms, providing, however, several important constraints. In the planetary ejection scenario, only a "hot Jupiter"-type planet with a semimajor axis of less than 1 AU can be responsible for the stream, and only if the disk was dynamically "heated" by a more distant massive planet. The radiation pressure scenario also requires the presence of a relatively massive planet at several AU or more, that had heated the cometesimal disk before the ejection occurred. Finally, the dust flux measured at Earth can be brought into reasonable agreement with both scenarios, provided that β Pic's protoplanetary disk recently passed through an intensive short-lasting (∼0.1 Myr) clearance stage by nascent giant planets, similar to what took place in the early solar system.