![]() ![]() (Mass, semi-major axis) of planets detected by transits. ![]() ![]() ( a) (M.sin(i), semi-major axis) of the planets detected by RV. Finally, in a few cases, spectroscopic observations of transiting planets allowed the first explorations of the atmospheres of hot (Teff≃2000 K) Jupiters.įigure 1. Dynamics is now also known to have played a major role in the building of the final architecture of our solar system, as shown by the Nice models. to planet scattering during close encounters, the presence of the third body (secular models) or early disc–planet interactions (disc migration models)) is needed to explain close in, retrograde planets and/or high eccentricity planets hence dynamical evolution plays an important role in the building of extrasolar planetary systems. One remarkable outcome of the studies is that dynamical evolution (owing e.g. An unexpected diversity of planet orbital properties (separations, eccentricities, orbital motions, e.g. There are indications that RV or transit planets were predominantly formed by the accretion of gas onto a solid core (‘core-accretion’ scenario hereafter CA ), like our solar system giants, rather than by gaseous collapse within a gravitationally instable (GI scenario ) disc. We know that exoplanets are frequent solar-type stars: around ≃15% of stars have planets with masses larger than 50 M Earth and more than 50% of that of planets (all masses ). ![]() Thanks to hundreds of discoveries ( figure 1 ) for almost 20 years, mainly coming from radial velocity (RV) and transit surveys, our knowledge on exoplanets has dramatically improved. Planet imaging: interest and challengesĮxoplanet science aims at answering three main questions: (i) How do planets form and evolve? (ii) What is the diversity of planetary systems (planet orbital and physical characteristics, mutiple systems architectures)? (iii) Can we identify planets suitable for the search of biosignatures? I finally present the progress expected in direct imaging in the near future, thanks in particular to forthcoming planet imagers on 8–10 m class telescopes.ġ. I also point out the limitations of this approach, as well as the needs for further work in terms of planet formation modelling. Individual and emblematic cases are detailed they illustrate what future instruments will routinely deliver for a much larger number of stars. In this paper, I present the results of direct imaging surveys obtained so far, and what they already tell us about giant planet (GP) formation and evolution. These few detections already challenge formation theories. So far, only a few planets have been imaged around young stars, but each of them provides an opportunity for unique dedicated studies of their orbital, physical and atmospheric properties and sometimes also on the interaction with the ‘second-generation’, debris discs. Direct imaging on 8–10 m class telescopes allows the detection of giant planets at larger separations (currently typically more than 5–10 AU) complementing the indirect techniques. These detections allowed the study of the planet populations in the first 5–8 AU from the central stars and have provided precious information on the way planets form and evolve at such separations. Most of the exoplanets known today have been discovered by indirect techniques, based on the study of the host star radial velocity or photometric temporal variations. ![]()
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