Exo-forecast: it鈥檚 foggy out there. For the first time, water vapour has been detected in the atmosphere of a Neptune-sized planet outside the solar system.
Previously, astronomers had found water in the atmospheres of so-called hot Jupiters, which are as massive or larger than Jupiter and orbit scorchingly close to their stars. But similar efforts for smaller planets had been stymied by hard-to-interpret data.
Now, of the University of Maryland, College Park, and colleagues have used the Hubble and Spitzer space telescopes to study , a planet 123 light-years away in the constellation Cygnus. With a radius four times that of Earth, it鈥檚 the smallest yet to have its atmosphere probed.
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In addition to water vapour, they found a lot of hydrogen, and some oxygen and heavier elements.
鈥淚t does look like a Neptune clone, only hotter,鈥� says planetary scientist of the Space Science Institute in Seabrook, Texas. This molecular profile suggests that the planet formed far from its star, then moved closer.
The observation is a 鈥渞ung on the ladder鈥� down to being able to study the atmospheres of Earth-like exoplanets, says of Grinnell College in Iowa.
It isn鈥檛 clear why other exo-Neptunes鈥� atmospheres have been so hard to probe. High clouds or a very compressed atmosphere of heavier molecules such as carbon dioxide might be to blame for the lack of signal. 鈥淚t has been an annoyance,鈥� says Kempton. 鈥淲e kept observing these planets that should be interesting and we鈥檝e see nothing.鈥�
Journal reference: Nature, DOI: 10.1038/nature13785
