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An international team of astronomers, including Carsten Dominik of the Anton Pannekoek Institute for Astronomy at the University of Amsterdam, has discovered a new exoplanet. It is the first planet to be discovered using ESO’s SPHERE-instrument.

The planet that was discovered is quite rare, explains Professor Dominik: ‘SPHERE is an instrument that was built specially for the observation of young, bright planets that revolve around their star neither too closely, nor too far off. These planets are surprisingly rare and it is spectacular that SPHERE is starting to find them. This category of planets is of crucial importance to us to understand how planets are formed.’

Puzzling questions

The planet, which was named HIP 65426b, is at a distance of some 385 light-years from us. HIP 65426b is warm (between 1,000 and 1,400 degrees Celsius), and is between six and twelve times the mass of Jupiter. It seems to have a very dusty atmosphere filled with thick cloud, and it orbits a hot, young star that rotates surprisingly fast. Unusually, given its age, the star does not appear to be surrounded by a disc of debris, and the absence of a disc raises puzzling questions about how the planet formed in the first place.

The exoplanet HIP 65426b — the first to be seen by the SPHERE instrument on ESO’s Very Large Telescope. The image of the parent star has been removed from the image. The circle indicates the orbit of Neptune around the Sun on the same scale. The planet is clearly visible at the lower-left in this remarkable image. Image: ESO

Evolution and physics of exoplanets

The discovery of HIP 65426b gives astronomers the opportunity to study the composition and location of clouds in its atmosphere, and to test theories of the formation, evolution, and physics of exoplanets. One possibility is that the planet was been formed in a disc of gas and dust and when the disc rapidly dissipated, interacted with other planets to move to a more distant orbit, where we see it now. Alternatively, the star and the planet may have formed together as a binary system in which the more massive component prevented the other would-be star from accumulating sufficient matter to actually become a star.

Cleverly designed

SPHERE is an acronym for Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. It is a powerful planet finder installed on the Very Large Telescope, a European Telescope in Chili. Its science goal is to detect and study new giant exoplanets around nearby stars using the direct imaging method. This method aims to directly capture images of exoplanets and debris discs around stars, rather like taking a photograph. Direct imaging is difficult because the light of a star is so powerful that the feeble light reflected by orbiting planets is overwhelmed by the starlight. But SPHERE is cleverly designed to bypass this obstacle and to look specifically for the polarised light reflected off a planet’s surface.

600 nearby stars

This image was captured as part of the SHINE (SpHere INfrared survey for Exoplanets) research programme. SHINE aims to image 600 young nearby stars in the near-infrared using SPHERE’s high contrast and high angular resolution to discover and characterise new planetary systems and explore how they formed.