The Chandra X-ray space telescope was used for the first time to detect the presence of an exoplanet. This is not a discovery because the planet in question is HD 189733b, more formally HD 189733 Ab, which was already in the spotlight a few weeks ago because the observations made with the Hubble Space Telescope established that its color is blue.
The planet HD 189733b is about 63 light-years away from Earth and was discovered in 2005. Its star, HD 189733 A, is an orange dwarf a little smaller than the Sun that has a companion, HD 189733 B (note the capital B!), a red dwarf that’s even smaller. Over the years there have been several observations of the planet but it became famous when the Space Telescope Imaging Spectrograph (STIS),an instrument on the Hubble Space Telescope, determined its color.
This study has allowed to notice that the brightness of the system decreases in the blue area of the electromagnetic spectrum when the planet passes behind its star. From this clue, the researchers deduced that the planet is blue thanks to that signal being constant compared to the other colors.
This discovery brought some confusion when some reporters who didn’t pay proper attention thought that the blue color was due to an ocean and described the planet as a possible Earth’s twin. Nothing could be more wrong! In reality, HD 189733b is bigger than Jupiter and is very close to its star, so much that its orbital period is just a little over two days.
Because of this proximity, the temperature on its surface is higher than 1,000 degrees Celsius (almost 2,000 Fahrenheit) so it’s a “hot Jupiter”, a category that includes the giant gas planets that have a very high temperature on their surface due to the proximity to their star.
The new observation of the planet HD 189733b made by NASA’s Chandra X-ray space telescope but also using data collected by ESA’s XMM-Newton space telescope allowed to discover something new about it. When the planet transits its star the decrease of X-rays is three times larger than the decrease of the visible light. This suggests that there are extensive layers of the planet’s atmosphere that are transparent to visible light but opaque to X-rays
The researchers also discovered something about the effects the planet HD 189733b and its star have on each other. The planet’s atmosphere is evaporating in time, more rapidly than they thought. Instead, the effect on the star seems positive because it looks younger than its age, probably because the planet is maintaining its rotation and its high magnetic activity due to tidal forces.
Possibly, further studies of the planet HD 189733b will reveal other surprises. Certainly what researchers have learned from the new approach in X-ray observations will be applied in the research on other exoplanets.
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