Now astronomers using NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM Newton Observatory have managed to catch sight of the planet as it eclipsed its sun using X-rays. This marks the first time that a planet has ever been observed in this manner.
This is actually similar to how HD 189733b was discovered in the first place. In 2005, French astronomers observed the planet transit in front of its star using the normal optical wavelengths that our eyes use. Indeed, most planets outside of our solar system have been discovered in this manner. When a planet transits, it causes part of the star’s brightness to dim as the planet passes in front of the star. Similarly, astronomers at Chandra and Newton viewed the planet pass in front of the star using X-ray wavelengths, noting a visible “dip” in the X-ray intensity of the planet’s star where HD 189733b passed in front of it.