Washington: Astronomers have for the first time, through X-ray observations, 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, which is 63 light-years from Earth, 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.
"Thousands of planet candidates have been seen to transit in only optical light," Katja Poppenhaeger of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led a new study, said.
"Finally being able to study one in X-rays is important because it reveals new information about the properties of an exoplanet," the researcher said
The team used Chandra to observe six transits and data from XMM Newton observations of one.
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.
HD 189733b is the closest hot Jupiter to Earth, which makes it a prime target for astronomers who want to learn more about this type of exoplanet and the atmosphere around it.
They have used NASA`s Kepler space telescope to study it at optical wavelengths, and NASA`s Hubble Space Telescope to confirm it is blue in color as a result of the preferential scattering of blue light by silicate particles in its atmosphere.
The study with Chandra and XMM Newton has revealed clues to the size of the planet`s atmosphere.
The spacecraft saw light decreasing during the transits.
The decrease in X-ray light was three times greater than the corresponding decrease in optical light. he findings are set to be published in The Astrophysical Journal.