Discovery of 30 exocomets in a young planetary system


For the past thirty years, the star β Pictoris has fascinated astronomers because it enables them to observe a planetary system in the process of formation. It is made up of at least two young planets, and also contains comets, which were detected as early as 1987. These were the first comets ever observed around a star other than the Sun. Now, an international research team headed by Alain Lecavelier des Etangs, CNRS researcher at the Institut d'Astrophysique de Paris (CNRS/Sorbonne Université)1 , has discovered 30 such exocomets and determined the size of their nuclei2 , which vary between 3 and 14 kilometres in diameter. The scientists were also able to estimate the size distribution of the objects, i.e. the proportion of small comets to large ones. This is the first time this distribution has been measured outside our Solar System, and it is strikingly similar to that of comets orbiting the Sun. It shows that, just like the comets of the Solar System, the exocomets of β Pictoris were shaped by a series of collisions and breakups. This work sheds new light on the origin and evolution of comets in planetary systems. Since a part of Earth's water probably originated in comets, scientists are seeking to understand their impact on the characteristics of planets. Their findings, published in Scientific Reports on April 28, 2022, are the outcome of 156 days of observation of the β Pictoris system using NASA's Transiting Exoplanet Survey Satellite (TESS). Other upcoming observations, in particular with the Hubble and James Webb space telescopes, should enable scientists to find out more in the future.

Artist's impression of exocomets orbiting the star β Pictoris.
©  ESO/L. Calçada
Light curves of a comet transiting its star. As predicted 20 years ago (right) and as observed for β Pictoris using TESS (left). The star's brightness dips when an object passes between it and the observer.
Right - © A. Lecavelier des Etangs et al. / Astronomy & Astrophysics 1999
Left - © A. Lecavelier des Etangs et al. / Scientific Reports 2022
  • 1Scientists from the Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (Observatoire de Paris - PSL /CNRS/Sorbonne Université/Université Paris Cité) and the Institut de Planétologie et d'Astrophysique de Grenoble (CNRS/UGA) also took part in this research.
  • 2A comet is formed primarily by a rocky core covered with dust and gas in the solid state. The tail of the comet appears only temporarily, when the frozen gases are warmed and enter the gaseous state.

Exocomets size distribution in the β Pictoris planetary system. Alain Lecavelier des Etangs, Lucie Cros, Guillaume Hébrard, Eder Martioli, Marc Duquesnoy, Matthew Kenworthy, Flavien Kiefer, Sylvestre Lacour, Anne-Marie Lagrange, Nadège Meunier and Alfred Vidal-Madjar. Scientific Reports, 28 Avril 2022. DOI:10.1038/s41598-022-09021-2


Alain Lecavelier des Etangs
CNRS researcher
François Maginiot
CNRS Press Officer