Secular resonances and cometary orbits in the β Pictoris system

THE dusty disk around the star β Pictoris is believed to contain a large number of comet-like bodies1,2. Transient absorption events associated with β Pictoris have been observed at many wavelengths3–6 and attributed to cometary objects on eccentric orbits passing between the star and the Earth7. One unexplained aspect of these events is the large asymmetry between red-shifted and blue-shifted features: ∼90% of the events are red-shifted6. We show here that such an asymmetry is a natural consequence of the influence on cometary orbits of secular resonances associated with some planetary systems. Results from numerical integrations of test particles in a model of our Solar System show that the v6secular resonance excites objects initially on near-circular orbits to high eccentricities while aligning their perihelia. Depending on the location of a distant observer, this alignment can produce an asymmetry similar to that observed for β Pictoris. Our results imply the presence of at least two planets (a prerequisite for the existence of secular resonances) around β Pictoris.