The first evidence of water-ice clouds on a world outside our solar system has been discovered, according to a study published today in the Astrophysical Journal Letters. Though water vapor has been detectedon extrasolar planets before, this is the only instance in which full clouds have been scoped out by astronomers.
This icy cloud world is a brown dwarf star formally known as WISE J085510.83-071442.5, but it goes by W0855 for short. It was only discovered a few months ago, by Penn State’s Kevin Luhman, a seasoned brown dwarf hunter. These weird failed stars are very difficult to root out because they never learned how to undergo nuclear fusion, and thus don’t produce starlight.
Indeed, at only 7.2 light years distant, W0855 is actually the fourth closest star to the Sun, but it’s so dim that it’s invisible in any wavelength shorter than infrared (excepting the occasional X-ray belch).
But W0855 is an odd duck even for this nebulous category. It is by far the coldest star ever found, wavering up to around only nine degrees Fahrenheit. No sooner was this freezing world discovered than astronomers were eager to see if it would provide the first evidence of water ice clouds outside of our solar system.
“The conditions had to be near-perfect from the ground in order for the detection to work,” lead author Jacqueline Faherty told me. “I needed clear, calm skies and everything had to work perfectly with the instrument.”
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