Une énorme quantité de travaux observationnels et théoriques ont été réalisés pour comprendre la physique et la chimie de la petite couche de gaz entourant les exoplanètes que l’on désigne aussi par le terme « atmosphère » . Avec l’aide d’observatoires spatiaux comme le télescope spatial Hubble ou l’observatoire infrarouge Spitzer, ou avec les derniers spectrographes au foyer des plus grands télescopes au sol, les données collectées sont aujourd’hui extrêmement riches en informations. La principale conclusion de ces vingt dernières années d’observations d’atmosphères d’exoplanètes est l’étonnante diversité des planètes qui ont été découvertes.
Nous nous intéressons ici à un phénomène particulier : l’évaporation d’exoplanètes qui sont en orbite très près de leurs étoiles. Nous décrivons les observations de l’échappement atmosphérique des exoplanètes. Puis nous montrerons les conséquences de ce phénomène sur les propriétés physiques des exoplanètes. Nous montrons que l’évaporation de petits corps est également observée dans certains systèmes extrasolaires, conduisant à la découverte d’exocomètes. Les observations spectroscopiques et photométriques ont permis de scruter les composantes de gaz et de poussières des queues cométaires. Enfin, les observations photométriques détaillées des exocomètes ont permis de mesurer les tailles des noyaux de comètes dans le système planétaire de β Pictoris ; la distribution de taille observée montre l’importance des collisions dans les dernières étapes de la formation des systèmes planétaires.
Here we review the last advances in our understanding of exoplanetary upper atmospheres, with a focus on the evaporation of exoplanets orbiting close to their stars. The atmospheric escape takes a significant part on the phenomena that sculpt the population of planets with short orbital distances.
We also observe evaporation of minor bodies in young planetary systems when they approach to their star. These “exocomets” have been studied since the mid 80’s, yielding a large amount of observational data. In particular, in the case of exocomets orbiting the young star β Pictoris, it has been shown that there are two different families of comets, tracing two different dynamical histories. Most recently, photometric observations with the NASA TESS space observatory allowed the detection of the dust tails produced by the evaporation of the exocomets’ nuclei. Using numerical simulation these observations allowed the derivation of the comets nuclei size distribution, which is found to be strikingly similar to the one observed in the Solar system and to the one expected for a collisionally relaxed population of minor bodies.
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Mot clés : Exoplanètes, Atmosphères, Exocomètes, Systèmes planétaires, Disques circumstellaires, Échappement atmosphérique, Bêta Pictoris
Alain Lecavelier des Etangs 1
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@article{CRPHYS_2023__24_S2_221_0, author = {Alain Lecavelier des Etangs}, title = {Evaporation, from exoplanets to exocomets}, journal = {Comptes Rendus. Physique}, pages = {221--231}, publisher = {Acad\'emie des sciences, Paris}, volume = {24}, number = {S2}, year = {2023}, doi = {10.5802/crphys.142}, language = {en}, }
Alain Lecavelier des Etangs. Evaporation, from exoplanets to exocomets. Comptes Rendus. Physique, Volume 24 (2023) no. S2, pp. 221-231. doi : 10.5802/crphys.142. https://comptes-rendus.academie-sciences.fr/physique/articles/10.5802/crphys.142/
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