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Atmosphere rich in water discovered around Neptune-sized world

13 May 2017

In a rare, detailed study of a far-off world known as a 'warm Neptune, ' an global team of researchers has revealed a planet with a primitive atmosphere and a strong water signature. The metallicity of HAT-P-26b was lower than would be expected for a planet of its size, suggesting the atmosphere is "young" and probably formed after the main body of the planet, without much subsequent contamination from space debris or impacts. Located about 437 light years away, HAT-P-26b orbits a star roughly twice as old as the sun.

Ice giants like our own solar system's Uranus and Neptune host higher concentrations of metallic elements because they formed along the outskirts of the sun's protoplanetary disk. The study, published in the journal Science, made three notable findings: The exoplanet has an atmosphere made up nearly entirely of hydrogen and helium, it has a relatively cloudless sky and it has a strong water signature.

In the atmosphere of this planet, in addition to hydrogen and helium, water is present.

A detailed study from University of Exeter researchers has discovered a "primitive atmosphere" that could shed light into how planets form similarly and differently in other solar systems.

The analysis of HAT-P-26b's atmosphere was done using both the Spitzer and Hubble space telescopes as the planet transits its star. By determining which wavelengths of light are absorbed and which aren't, researchers can work backward to derive the chemical composition of the atmosphere.

Using data from the Hubble telescope's Imaging Spectrograph and Wide Field Camera as well as Spitzer's Infrared Array Camera, the research team derived the transmission spectrum of HAT-P-26b, with the measurements best fitting a profile pointing to distinct water absorption and uniform cloud opacity. "And we didn't know before that you could form [such] planets in that region".

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In the Solar System, the metallicity in Jupiter (5 times greater than the Sun) and Saturn (10 times) suggest these "gas giants" are made nearly entirely of hydrogen and helium.

"This analysis shows that there is a lot more diversity in the atmospheres of these exoplanets than we were expecting, which is providing insight into how planets can form and evolve differently than in our Solar System", one of the team, David K. Sing from the University of Exeter in the United Kingdom, explains in a press release. Water serves as a representative of all the elements in the atmosphere heavier than hydrogen and helium.

Astronomers have discovered a primitive atmosphere surrounding a "Warm Neptune" exoplanet, a Neptune-like world orbiting closer to its host star.

In our solar system and two planets outside our solar system, the general trend observed among the gassy planets is that larger planets have smaller amounts of heavy elements.

"Not too long ago, it was exciting just to find an exoplanet", said Drake Deming, a professor of astronomy at UMD and a co-author of the study.

Atmosphere rich in water discovered around Neptune-sized world