HD209458b, also called Osiris, was discovered in 1999 via Doppler spectroscopy, and entered the astronomical hall of fame when it passed in front of its parent star and eclipsed it. In 2001 Hubble detected the element sodium in the lower part of the planet’s atmosphere. In 2003 hydrogen was detected in its upper atmosphere. In 2004, oxygen and carbon were detected in the upper atmosphere. Today, HD209458b is considered to be a part of a new class of extrasolar planets proposed, called the chthonian planets, as the cores of these giant planets are primarily comprised of evaporated gas.
In the July 10th issue of The Astrophysical Journal it has been reported that the Hubble Space Telescope astronomers have confirmed the existence of a tortured, baked object that they are calling a cometary planet. Now, observations by the new Cosmic Origins Spectrograph (COS) aboard NASA 's Hubble suggest that powerful stellar winds are sweeping the castoff material behind the scorched planet and shaping it into a comet-like tail. (HubbleSite)
Cited: Choi, Charles Q. "Untitled Document." Space.com. Web. 31 October 2010. . "HubbleSite - NewsCenter - Superhot Planet Likely Possesses Comet-like Tail (07/15/2010) - The Full Story." HubbleSite -- Out of the Ordinary...out of This World. Web. 31 October 2010. . NASA Release 10-167. NASA Finds Super Hot Planet With Unique Comet-Like Tail." NASA - Home. Web. 31 October 2010. .