Séminaire IPAG

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Dynamics of the Beta Pictoris planetary system and its exocomet population

jeudi 14 mars 2024 - 11h00

Hervé Beust & Antoine Lacquement - IPAG
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The Beta Pictoris disk is the historical prototype of debris disks, under investiations for almost 40 years now. The disk is now known to harbour two giant planets, Beta Pic and c, orbiting the star at 9.9\,au and 2.7\,au, but other still unknown planets could be present. This 20 Myr old system represents a likely analogue of the young Solar System. For decades, spectral variations in the visible and UV spectrum of Beta Pictoris have been modelled as the result of the evaporation of exocomets close to the star, termed falling evaporating bodies (FEBs). Resonant perturbations by a hypothetical giant planet have been proposed to explain the dynamical origin of these stargrazers. Actually Beta Pic b almost matches the planet formerly suspected, but the recent discovery of Beta Pic c complicates the picture. We first question the stability of the two-planet system. Then we investigate the dynamics of a disk of planetesimals orbiting the star together with both planets to check the validity of the FEB generation mechanism, using dedicated N-body simuations. We first determine which regions of the planetesimal disk are dynamically stable and which are not. Then we focus on regions where disk particles are able to reach high eccentricities, mainly thanks to resonant mechanisms. The first result is that the system is dynamically stable. Both planets may temporarily fall in 7:1 mean motion resonance (MMR). Then, the simulations reveal that the whole region extending between ~1.5 au and ~25 au is unstable to planetary perturbations. However, a disk below 1.5 au survives, which appears to constitute an active source of FEBs via high-order MMRs with Beta Pic c. In this new picture, Btea Pic b acts as a distant perturber that helps sustain the whole process. According to this new picture, FEBs are likely to originate from a region much further in and related to MMRs with Beta pic c. That mechanism also appears to last longer, as new planetesimals are able to continuously enter the MMRs and evolve towards the FEB state. Subsequently, the physical nature of the FEBs may differ from that previously thought, and presumably may not be icy. Similar simulations are also used to question the presence of additional planets orbiting the star outside Beta Pic b's orbit. Various modeling of the observed disk converge towards a disk of planetesimal truncated inwards at ~50 au. However, our simulations shwo that Beta Pic b & c alone are only able to carve the disk up to ~27 au at most. Hence we suppose that an additional planet may be resopnsible for the carving up to 50 au. Taking into account upper limits deduced from high contrast imaging and using N-body simulations, we derive constraints on the characteristics of this putative planet. A two-planet solution may also be possible.

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Hôtes : Jérôme Bouvier

Salle Manuel Forestini, 414 rue de la piscine, 38400 Saint Martin d'Hères