A team of astronomers led by the University of California Santa Cruz has found strong evidence of water clouds on a brown dwarf called WISE 0855—the first time that clouds of water have been detected outside the solar system. WISE 0855 is only 7.2 light years from Earth, but it is difficult to observe because it is so cold and dim. The team's findings were recently published in Astrophysical Journal Letters.

A brown dwarf is an object too big to be a planet, but too small to be a star. Its life begins just like a normal star—gas and dust collapse due to gravity into a large spherical object. The difference is that the mass of the object never gets high enough to ignite the nuclear fusion process that powers a star. WISE 0855 is about five times the mass of Jupiter, and at about minus 10 degrees Fahrenheit, the brown dwarf is the coldest known object outside the solar system.

"WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants," said Andrew Skemer, an assistant professor of astronomy and astrophysics at UC Santa Cruz, in an announcement. "We would expect an object that cold to have water clouds, and this is the best evidence that it does."

Because WISE 0855 is so dim, traditional spectroscopy techniques could not be used to determine its composition. Instead, the Gemini-North telescope in Hawaii was used to observe the brown dwarf for about 14 hours a night for 13 nights. Thermal emissions from the deep atmosphere of the celestial body made spectroscopy possible, though difficult.

"Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter," said Skemer.

Cold objects outside the solar system are incredibly difficult to detect, but future observations of brown dwarfs like WISE 0855 could help us figure out how common water vapor is in the galaxy.

Source: University of California Santa Cruz

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