Exoplanets - planets around stars other than the sun - were discovered almost 20 years ago,but for the first time, X-ray observations have detected an exoplanet passing in front of its parent star.
An advantageous alignment of a planet and its parent star in the system HD 189733, 63 light-years from Earth, has enabled NASA's Chandra X-ray Observatory and the European Space Agency's XMM Newton Observatory to observe a dip in X-ray intensity as the planet transited the star.
The planet, known as HD 189733b, is a hot Jupiter, meaning it is similar in size to Jupiter in our solar system but in very close orbit around its star. HD 189733b is more than 30 times closer to its star than Earth is to the sun. It orbits the star once every 2.2 days.