Hubble haze study of nearby exoplanet released

A Hubble space telescope look at the chemistry of a nearby star's "evaporating" planet finds it likely adorned with a uniform blue haze.

HD189733b made headlines in 2005 when astronomers first detected its "transit" (or eclipse) of its it star, some 63 light years away (one light year is 5.9 trillion miles). The gas giant planet roasts in close orbit around its star, likely broiling at more than 1,880 degrees Fahrenheit, according to the study in the Monthly Notices of the Royal Astronomical Society led by D. K. Sing of the United Kingdom's University of Exeter.

"Transiting planets now allow the possibility of detecting and studying extrasolar planets, from their formation and statistical properties, to the bulk composition of the planets themselves as well as their atmospheres. Atmospheric information on exoplanets can be gathered in several different ways. During a transit, an exoplanet passes in front of its host star, with some of the stellar light filtered through the planet's atmosphere, making it possible to perform transmission spectroscopy. Optical and infrared measurements during secondary eclipse can be used to obtain an exoplanet's dayside emission spectra, where such properties including the temperature, thermal structure and composition can be measured. Finally, orbital phase curves can probe the global temperature distribution and study atmospheric circulation," says the study.

In 2008, a Spitzer space telescope team reported signs of carbon dioxide in the atmosphere of the planet, which is steadily evaporating away in its close cooking by its star. The latest study looked for signs of clouds in chemistry discernible from its light signature.

Instead of the turbulent cloudy features suggested by data from the other exoplanet (HD 209458b) eyeballed for atmospheric chemistry, HD189733b looks like it possesses a bluish haze of an atmosphere.

As usual, the results suggest that exoplanets are even weirder than we might have first supposed, and come in all flavors:

"The list of key differences between the two well studied hot Jupiters is growing, with HD 209458b likely featuring a low albedo, stratospheric temperature inversion, inflated planetary radius and large (sodium) alkali line wings, while HD 189733b has a high albedo, no stratospheric temperature inversion, a non-inflated planetary radius and a global haze covering significant alkali line wing absorption. Such differences point toward a large diversity between the broader class of hot-Jupiter atmospheres, as HD 209458b and HD 189733b only differ by a few hundred degrees," concludes the study.