ESO’s SPHERE Unveils a Unique Exoplanet

One of the most challenging and exciting areas of astronomy today is the search for exoplanets — other worlds orbiting other stars. The exoplanet HIP 65426b has recently been discovered using the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch instrument) instrument on ESO’s Very Large Telescope (VLT). Some 385 light-years from us, HIP 65426b is the first planet that SPHERE has found [1] — and it turns out to be a particularly interesting one.

The planet is warm (between 1000 and 1400 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 planet may have been formed in a disc of gas and dust and when the disc rapidly dissipated, it 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. The planet’s discovery 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.

SPHERE is a powerful planet finder installed on Unit Telescope 3 of the VLT. Its science goal is to detect and study new giant exoplanets around nearby stars using the direct imaging method [2]. 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.

This image was captured as part of a survey programme called SHINE (SpHere INfrared survey for Exoplanets). 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.

Notes

[1] A previous ESO press release reported an earlier SPHERE observation that was interpreted as a planet. However, that interpretation has been called into doubt and so HIP 65426b is currently the first reliable detection of an exoplanet by SPHERE.

[2] When scouring the Universe for exoplanets, astronomers have numerous tools at their disposal. Many planet detection methods are indirect — astronomers can detect the tell-tale dip in a star’s brightness when a planet transits across its face, or measure the tiny wobble in a star’s motion caused by the gravitational tug of any orbiting planets. However, there is a more direct method of finding an exoplanet: direct imaging.

Courtesy of European Southern Observatory