Exoplanet-hunter SPHERE achieves first light
By Anthony Wood
June 6, 2014
A new scientific instrument for detecting and observing remote exoplanets has been successfully installed on Unit 3 of the European Southern Observatory's (ESO) Very Large Telescope (VLT). The Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, or SPHERE, recently returned its first set of images and is promised to revolutionize the exploration and study of these distant celestial bodies.
SPHERE is the child of numerous space agencies from around the world, headed by the Institut de Planétologie et d'Astrophysique de Grenoble, France, in partnership with the ESO. The primary target for the new instrument is the discovery and subsequent study of giant exoplanets roughly the size of Jupiter. It is anticipated that SPHERE will greatly outperform all previous missions in the field of exoplanet observation, boasting the ability to observe these distant stellar companions directly through a combination of state-of-the-art techniques.
Until now only indirect observation of these far-off bodies had been possible, as an exoplanet is generally very close to its parent star, and the light thrown out by this star overwhelms the relatively weak shine of the exoplanet. Therefore astronomers had to employ indirect methods of detection, such as measuring the dip in light from the parent star as the companion planet transits across its face. SPHERE, on the other hand, was designed to achieve the highest possible level of contrast whilst observing a narrow field of view, which when combined with the techniques we are about to outline, allows SPHERE to observe exoplanets directly in exceptional detail.
SPHERE employs a combination of three advanced techniques to image the exoplanets. They include adaptive optics designed to combat the distorting effects of Earth's atmosphere, and an advanced coronagraph, used to block some of the light from the nearby parent star which ordinarily shields the exoplanet from view.
The third technique utilized by SPHERE is known as differential imaging, an observational trick that measures the amount of starlight that scatters off the exoplanet's atmosphere, becoming polarized in the process. Differential imaging can then separate the now-polarized light from the glare of the parent star, granting a much clearer view of the exoplanet. Using these three techniques in concert, SPHERE will be able to reveal exoplanets that have never been successfully directly imaged before, greatly heightening our understanding of the solar systems orbiting distant stars.
The first light observations targeted a number of celestial bodies best suited to testing the capabilities of the various viewing modes available to SPHERE, resulting in some remarkable images. It is planned for SPHERE to be made available to the scientific community at large later this year following further extensive testing.