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Water Clouds Observed in a Distant Star System

Artist's conception of how WISE 0855 might appear if viewed close-up in infrared light. Artwork by Joy Pollard, Gemini Observatory/AURA.

Artist’s conception of how WISE 0855 might appear if viewed close-up in infrared light. Artwork by Joy Pollard, Gemini Observatory/AURA.

Our galaxy is full of with brown dwarfs, which are failed stars filling a gap between planets and stars. At present, astronomers could make a very important discovery through studying a nearby brown dwarf.

A team based at UC Santa Cruz has got the first infrared spectrum of the brown dwarf named as WISE 0855, the coldest single object outside of the Solar System, which is only 7.2 light-years away from Earth. Apart from many interesting features, astronomers also found out that just like Jupiter, the object is dominated by atmospheric bands,  and it has a cover of water clouds.

As Andrew Skemer, lead author, said in a statement, this object was five times fainter than any other one detected with ground-based spectroscopy at this wavelength. Since they had a spectrum, they could really begin to think  about what was going on in this object. Their spectrum revealed that WISE 0855 was dominated by water vapor and clouds, that appeared to be amazingly similar to Jupiter.

Brown dwarfs fall into the catalog of almost-stars, which were not big enough to ignite a nuclear fusion reaction at their core. Like stars, they are formed with the same elements, although they are quite warm when they first create, over time they turn to be cooler and cooler.

Based on the newest analysis, which is going to be published in Astrophysical Journal Letters and currently available on arXiv, WISE 0855 has a temperature of -23°C (-10°F). It is quite tough to do spectroscopic analysis on such a cold and far away object, so it has taken almost 14 hours of observations over 13 nights for the light spectrum to observe the incredible new details of this extrasolar world.

As Skemer said, WISE 0855 was their first chance to examine an extrasolar planetary-mass object, because it was nearly as cold as our own gas giants.

An interesting difference between WISE 0855 and Jupiter is the shortage of phosphine in the brown dwarf. Phosphine is kind of toxic gas created in the hot interior of gas giants. In order that it could move to the outer atmosphere, turbulent motion is necessary, which infers  that compared with Jupiter, WISE 0855 has a much calmer atmosphere.

This research demonstrates how the distinction between gas giant planets and brown dwarfs is in fact quite arbitrary. In the future, researchers will likely go further into the similarities between failed stars and large planets.

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