...to the dynamics of planetary systems

If the techniques of high angular resolution have provided general representations of protoplanetary disks they have also enabled studies at the very smallest scale to be carried out, indispensable to an understanding of the formation of planets. In effect it is through the collision of grains that larger and larger agglomerates form, up to the point of giving birth to the planets. Thus, when a disk dissipates it gives place to planets, but also to a multitude of other bodies (comets, asteroids, etc.) which, in colliding with each other, produce second generation dust which forms a disk of debris.  ‘The study of several of these debris disks has led to the appearance of strange structures, such as a star surrounded by a disk which ends abruptly, instead of fading out gradually,’ recounts Olivier Absil. ‘The dynamics of the dust could only explain it by the presence of a companion planet. Observations in 2004, repeated in 2006, brought to light the theoretically predicted intruder. It’s a very great result which brings together observation, modelling and prediction. It was the subject of a publication in Nature in 2008.’

Amongst the crop of high angular resolution observations let us mention once again the case of β-Pictoris, a nearby young star seen from the Southern hemisphere. This case is interesting as the star has a warp in its disk, which has been known of since 2001: the disk’s inclination is not the same in its interior and its exterior, as if it had two disks. This warp has been interpreted as the sign of the presence of a disruptive planet which is attracting towards itself material from the primary disk, thus indirectly forming a second. This companion was finally observed last year, exactly in the place predicted.