For the first time since exoplanets were discovered almost 20 years ago, 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, 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.
The planet, known as 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.
The study with Chandra and XMM Newton has revealed clues to the size of the planet’s atmosphere. “The X-ray data suggest there are extended layers of the planet’s atmosphere that are transparent to optical light but opaque to X-rays,” said Jurgen Schmitt of Hamburger Sternwarte. “However, we need more data to confirm this idea.”
The researchers also are learning about how the planet and the star can affect one another.
For about a decade astronomers have known that ultraviolet and X-ray radiation from the main star in HD 189733 are evaporating the atmosphere of HD 189733b. The authors estimate it is losing 100 million to 600 million kilograms of mass per second. HD 189733b’s atmosphere appears to be thinning 25 per cent to 65 per cent faster than it would be if the planet’s atmosphere were smaller.
The findings will be published in the Astrophysical Journal.
Source: Chandra X-ray Centre