3.2 Super-Jupiter exoplanets
The core-accretion scenario discussed so far has its origin in the search for an explanation for our Solar System which, until the discovery of 51 Pegasi b, was the source of all available observational data used to constrain planet-formation theories. While, in its modern form, the core-accretion scenario succeeds in explaining some of the characteristics of the observed exoplanet population, there are still some aspects of planet formation that the model struggles to describe. One such aspect is connected with the formation of giant planets and, in particular, of directly imaged planets in wide orbits.
As briefly mentioned in Section 3.1, the main problem with the growth of giant planets via core accretion is connected with the lifetime of the discs, which appear to have gas-dissipation timescales that are too short to allow for the formation of many of the observed gas-giant exoplanet systems. This is true for Jupiter-sized exoplanets, but becomes even more crucial when considering the directly imaged super-Jupiters (exoplanets with masses several times that of Jupiter), like the one orbiting the young solar-type star YSES 2 (named after the Young Suns Exoplanet Survey). The YSES 2 planetary system, which is part of the Scorpius–Centaurus association, is shown in Figure 8. The giant exoplanet YSES 2 b, which is visible as a bright dot indicated with the arrow in the figure, has a mass of about 6 Jupiter masses and a semimajor axis of around 110 au, and is one of the few directly imaged planets around a solar-type star.
