When do aging brown dwarfs sweep the clouds away?

Brown dwarfs, the larger cousins of giant planets, undergo atmospheric changes from cloudy to cloudless as they age and cool. A team of astronomers led by Carnegie's Jonathan Gagné measured for the first time the temperature at which this shift happens in young brown dwarfs. Their findings, published by the Astrophysical Journal Letters, may help them better understand how gas giant planets like our own Solar System's Jupiter evolved.

Brown dwarfs are too small to sustain the hydrogen fusion process that fuels stars and allows them to remain hot and bright for a long time. After formation, brown dwarfs slowly cool down and contract over time—at some point shifting from heavily cloud covered to having completely clear skies.

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Credit: NASA/JPL, slightly modified by Jonathan Gagné

Artist's conception of a different brown dwarf to the one studied by Jonathan Gagné and his team. The brown dwarf depicted here is also part of a moving group, although a different one than AB Doradus.

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Astronomers have discovered a "rogue planet" that seems to be travelling with a set of young stars -- called the AB Doradus Moving Group -- but isn't orbiting any of them. If it's part of that family, scientists can gauge.

The coldest brown dwarf star known to exist has been discovered by NASA's Wide-field Infrared Survey Explorer and the Spitzer Space Telescope.

It is the fourth closest star to our own at 7 point 2 light-years away, and is as cold as the North Pole on Earth with temperatures reaching between negative 54 and negative 9 degrees Fahrenheit.

Brown dwarf stars don't have enough mass to burn nuclear fuel like other stars, and can be easily missed when viewed from a visible light telescope, so astronomers were only able to see it using infrared light.

The star is estimated to be around 3 to 10 times the size of Jupiter, making it one of the smallest brown dwarfs known to exist in the universe.

That means it could be a gas giant, but experts think that it is actually a brown dwarf star.