Astronomers have caught the first glimpse of a snowy star.
More than 1,300 light-years away, the star V188 Orionis not only has snow, but more importantly, snow composed of water. Scientists found the first evidence of a snow line—similar to those found in the mountains—in a young planetary disk surrounding the star. Researchers at Atacama Large Millimeter/submillimeter Array (ALMA) announced the discovery this week in the journal Nature .
Snow lines form in solar systems around young stars. The stars are surrounded by dense, rotating disks of gas and dust, which include water. The heat radiating off the star means the water is usually gaseous up to a certain distance. But as you move farther from the star, the pressure becomes lower and water molecules sublimate, creating the water snow line.
Here’s Mary Beth Griggs reporting for Popular Science:
A snow line in a solar system is in some ways very similar to a snow line on a mountain slope here on Earth. In some places, on a winter day, you might notice that snow is sticking to the ground at higher elevations, forming a visible line between colder highland areas and warmer lowland ones.
The idea is similar in a solar system that contains water. When the water is closer to the sun, it hangs out as a gas, floating through space, but when it gets further out, the gas sublimates or turns into a solid, forming snow in space.
Just three years ago, scientists found planetary snow around the star TW Hydrae. But the snow line they found then was composed of carbon monoxide. Unlike carbon monoxide snow lines, water snow lines are much more difficult to spot and capture a clear image of. This is because they usually circle the star at a distance of three astronomical units (au), which is hard to detect due to how close it is.
In this discovery, the water snow line is an astonishing 40 au away from its star, V883 Orionis. (For reference, Pluto is about 40 au from the Sun.) This unusual snow line location was due to a dramatic increase in the star’s brightness, which caused the snow line to be pushed out.
Studying snow lines aids the development of reliable planetary models, since the formation of snow lines is recognized as an important step in the formation of new planetary systems.