Free Astronomy Magazine July-August 2014

INSTRUMENTS different polari- zation levels that characterize the starlight and the planetary light. Even though a planet seemingly reflects only the light of its star, the reflected sig- nal does in ac- tual fact contain additional infor- mation about the planetary at- mosphere (as well as the Earth’s atmo- sphere) and, in the infrared domain, also the information related to the internal heat, that limits the disparity in brightness in re- spect to the star. In addition to these remark- I mages taken with different techniques by SPHERE, of the star HR 7581 (Sag- ittarius constella- tion), invisible at the centre of the image. The white dot is a faint companion star (4000 times less bright than HR 7581) separated by only 0.24 arc- seconds. Below: infrared image of Titan (the disk is 0.8 arcseconds). [ESO/J.-L. Beuzit et al./SPHERE Consortium] able solutions, SPHERE also has a little trick up its sleeve for highlighting possible arte- facts (and possible new planets) in the ac- quired images. In fact, it quite often hap- pens to see photographs of stellar disks with