Astronomers Detect Hot Jupiter Exoplanet with X-Ray Observations

About 63 light-years from Earth, a planet orbits its parent star in the system HD 189733. Now, for the first time since exoplanets were discovered almost 20 years ago, astronomers have used X-ray observations to detect this planet as it passed in front of its star.

The planet, known as HD 189733b, is a hot Jupiter. This means that it's similar in size to the massive planet in our own solar system, but is in very close orbit around its star. In fact, the exoplanet is more than 30 times closer to its parent star than Earth is to the sun, orbiting it once every 2.2 days. Since it's the closest hot Jupiter to Earth, it's a prime candidate for astronomers who want to learn more about this type of exoplanet.

In order to actually receive a better look at HD 189733b, the researchers employed NASA's Chandra X-ray Observatory along with the European Space Agency's XMM Newton Observatory. This allowed the astronomers to observe a dip in X-ray intensity as the planet transited the star. Since these observations were done in X-ray, the scientists were able to learn a bit more about the exoplanet.

"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, co-author of the new paper describing the findings, in a news release. "However, we need more data to confirm this idea."

The exoplanet doesn't just have an unusual atmosphere though. It and its parent star are interacting in interesting and unusual ways. Ultraviolet and X-ray radiation from the main star are evaporating the atmosphere of the planet over time. In fact, astronomers estimate it's losing 100 million to 600 million kilograms of mass per second. This means that the exoplanet's atmosphere is thinning 25 to 65 percent faster than it would if the planet had a smaller atmosphere.

Then there's also the fact that the parent star is acting more like a younger star than the older star that it is.

"The star is not acting its age, and having a big planet as a companion may be the explanation," said Katja Poppenhaeger, one of the researchers, in a news release. "It's possible this hot Jupiter is keeping the star's rotation and magnetic activity high because of tidal forces, making it behave in some ways like a much younger star."

The findings reveal a little bit more about this hot Jupiter and its star. In addition, it shows researchers how these particular exoplanets act, showing them a little bit more about how our universe works.

The findings are published in The Astrophysical Journal.