Astronomers Discover Water Clouds on the Coldest Known Object Outside Our Solar System

Friday, 08 July 2016 - 2:17PM
Astrobiology
Friday, 08 July 2016 - 2:17PM
Astronomers Discover Water Clouds on the Coldest Known Object Outside Our Solar System

Astronomers have just discovered strong evidence that the brown dwarf WISE 0855 has clouds in its atmosphere made of water or water ice. But for those of you envisioning extraterrestrials or a new human habitat, there's a catch: it's the coldest object in the universe that we know of, aside from gas giants in our own solar system.

WISE 0855 is a close neighbor, only 7.2 light years away from Earth. It's a brown dwarf, which is our name for objects thought to be "failed stars," which are too large to be planets but too small to be considered stars. They are also extremely cold, too cold to emit visible light, so they can generally only be seen using infrared telescopes, which can detect the small amounts of heat radiating from the object. But WISE 0855 is so cold, it can barely be seen even with our largest infrared telescopes, leading astronomers to conclude that it is the coldest known object outside of our solar system. 

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"WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants," said lead author Andrew Skemer, assistant professor of astronomy and astrophysics at UC Santa Cruz, in a statement.
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Previous studies of this mysterious object had indicated the possibility of water clouds, but since it's so difficult to observe, they were never confirmed. For the new study, published in Astrophysical Journal Letters, researchers used the Gemini-North telescope in Hawaii and the Gemini Near Infrared Spectrograph to observe WISE 0855 at very specific wavelengths within 5 microns, which allowed them to see heat emissions from the deep atmosphere. They observed the object for 13 nights, a total of about 14 hours, and were just barely able to determine the molecular composition of the atmosphere. They created models of the atmosphere based on different compositions, including cloudy and non-cloudy, and found that water clouds yielded the best fit with the spectoscopy of WISE 0855.

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"It's five times fainter than any other object detected with ground-based spectroscopy at this wavelength," said Skemer. But they were still able to come to a tentative conclusion: "Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter."
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They found that WISE 0855 resembles Jupiter in many ways, although it's thought to be about five times more massive. Most notably, it is nearly as cold as Jupiter, with a temperature of about 250 degrees Kelvin, or minus 10 degrees Fahrenheit (Jupiter, for comparison, is about 130 degrees Kelvin). 

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"We would expect an object that cold to have water clouds, and this is the best evidence that it does," Skemer said.
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