The Kepler Space Telescope was launched by NASA in March 2009, with the express intention of looking for Earthlike planets. To this end it is located in Earth's trailing Lagrange point (i.e. it is situated on the same orbital pathway as Earth, but considerably behind us) to avoid interference from Earth and is aimed constantly at a single patch of the sky, taking in parts of the constellations of Cygnus, Draco and Lyra, to build up a very detailed picture of the stars there.
The Kepler Field of View, in relation to the Milky Way.
As well as some well publicized discoveries of rocky planets, Kepler has been building up a detailed picture of other objects in the field of view, including candidate planets of other types. One of these, KOI 203-b (KOI = Kepler Object of Interest), has been the subject of a study by a group of scientists led by Jean-Michel Désert of the Harvard-Smithsonian Centre for Astrophysics. Now that team have published a paper on the arXiv online forum maintained by Cornell University Library, in which they confirm KOI 203-b is a Hot Jupiter type planet, and rename it Kepler 17-b.
Kepler 17 (the star about which Kepler 17-b spins) is a dim star in the constellation of Cygnus. The study showed it is almost identical to our sun in mass and radius, though it is somewhat younger, ~2.9 billion years old as opposed to ~4.5 for our sun, and highly prone to sunspot activity. This sunspot activity made it hard to confirm that Kepler 17-b is in fact a planet rather than another sunspot, since both a sunspot and a planet are dark objects moving across the surface of the star. However repeated observations with the Kepler Space Telescope, the Hobby-Eberly Telescope, the Fred Lawrence Whipple Observatory, the Keck High Resolution Echelle Spectrometer and the Spitzer Space Telescope revealed that Kepler 17-b had a repeated cycle unlike that produced by a sunspot, and provided a limited amount of information about its atmosphere.
Kepler 17-b orbits its host star roughly once every 36 hours, in a roughly circular orbit, edge on to our solar system. It has a mass approximately 2.45 time that of Jupiter, and a radius approximately 1.3 times that of Jupiter. Its atmosphere is probably not inverted (i.e. it is probably warmer in the lower parts of the atmosphere, and cooler higher up), with gaseous Titanium Oxide and Vanadium Oxide present in the upper atmosphere. It is possible that the atmosphere is inverted (i.e. warmer above, cooler below) and that it contains gaseous Sodium and Potassium in its upper atmosphere.
Image of Kepler 17 (centre) taken with the Kepler Space Telescope.