Artist’s impression of exoplanet HD 209458b with comet-like tail

This artist's illustration shows a view of the gas giant planet HD 209458b, as seen from the surface of a hypothetical nearby companion object. The planet is orbiting so close to its sunlike star that its heated atmosphere is escaping into space. Spectroscopic observations by the new Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope suggest that powerful stellar winds are sweeping the castoff material behind the scorched planet and shaping it into a comet-like tail.

Image Credit: NASA, ESA, and G. Bacon (STScI)
Explanation from: https://www.spacetelescope.org/images/opo1021a/