Finding exoplanets these days has become blas, yet taking an image of one remains exceedingly difficult. So difficult that, of the thousands of exoplanets discovered, only a handful have been found through imaging. Against the odds, a team of European astronomers has just directly imaged a new giant exoplanet orbiting the star HIP 65426. This planet is roughly the size of Jupiter, but has an estimated six to twelve times the mass of the jovian giant. Its characteristics make the exoplanet a unique object not easily explained by existing models of planet formation.
Not just another planet HIP 65426b resembles Jupiter in size, but any comparisons end there. Not only is the exoplanet more massive than its jovian cousin, but its much hotter, coming in around a toasty 1,880-2,420F (1,026-1,326C). Based on models that match the data to simulations, the astronomers expect HIP 65426b has a dusty atmosphere, thick with clouds. The exoplanet was found at 92 AU from its star, putting it at three times the distance Neptune is from the Sun. The discovery has been detailed in a paper accepted for publication in Astronomy and Astrophysics.
Despite more than 3,000 exoplanets discovered to date, we are far from understanding how giant planets form, which is vital as they represent the largest mass within the planetary systems they completely shape, says Gal Chauvin, lead author on the paper and researcher at University of Grenoble and the University of Chile. They also play a key role in the dynamics of smaller planets similar to Earth, and therefore to ultimately understanding how life forms. The group of European astronomers who made the discovery has been at work in the Atacama Desert of Northern Chile at the Very Large Telescope for three years, conducting a survey of 600 young, nearby stars. Now halfway through their survey, they have discovered many potentially planet-forming disks around their surveyed stars, but HIP 65426b is the first exoplanet they have discovered. Another similar campaign, the Gemini Planet Imager Exoplanet Survey, has also only racked one exoplanet discovery to date, though multiple new disks and brown dwarfs have been found.
These results show that giant exoplanets at wide separations from their host stars are much less common than initially expected.
Picture-perfect Taking a snapshot of an exoplanet is all but impossible for anything but the youngest and brightest exoplanets. In order for the exoplanet to show up against the blinding glare of the host star, the planet needs to be bright itself, and young planets, still radiating their own light from formation, are ideal candidates for this technique. Specialized instruments have been designed with coronagraphs, which block the light of the star and allow the astronomers to see the fainter exoplanets. Current technology limits these instruments to seeing only wide-orbit exoplanets. Consequently, this technique is thus complimentary to the more common radial velocity method, which watches for wobbles in the stars movements and is most sensitive to giant planets on close orbits.
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New exoplanet challenges formation models - Astronomy Magazine