When you look at a snow-capped mountain, the line that separates the snow-less lower slopes and the snowy peak is descriptively known as a "snow line." It's above this line where you'd want to go with your snowboard or skis. Now, for the first time, astronomers have discovered the snow line for a particularly frosty star system 175 light-years away - but there's no word on the quality of the snow for slaloming.
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Stellar snow lines work in a similar way to their terrestrial mountain counterparts. On a mountain, there's a certain altitude where the atmosphere becomes so cold that water will freeze and snow will collect around the frozen mountain peak. Around a star, on the other hand, there's a certain distance from the hot star where it becomes so cold that it allows water (and other volatiles, such as methane) to freeze as ice particles.
Astronomers using the brand new Atacama Large Millimeter/submillimeter Array (ALMA) in Chile have used a neat little trick to resolve the stellar snow line around the young sun-like star TW Hydrae. And by doing so, they have taken a glimpse at what our solar system may have looked like during the early stages of its evolution.