Supersonic rain has been spotted falling around an embryonic solar system. Scientists using NASA’s Spitzer Space Telescope detected five times the water in all Earth’s oceans raining down on a disk of material around a still-forming star (Reuters and Space.com). “Water … exists mostly as ice in the dense clouds that form stars,” said researcher Dan Watson of the University of Rochester (press release). “Now we’ve seen that water, falling as ice from a young star system’s envelope to its disk, actually vaporizes on arrival. This water vapor will later freeze again into asteroids and comets.”

As Watson explained to Wired, the material reaches supersonic speeds before it crashes into the disk that will probably go on to form planets. The ice vaporizes on impact and vapour emits a spectrum of infrared light which can then be detected on Earth. “That light is what we measured. From the details of the measured spectrum we can tease out the physical details of this brand-new, pre-planetary disk.”

Unfortunately ‘supersonic’ in this context may not be as impressive as it sounds. Speed of sound is approximately proportional to density – as the local density is low, relative to air, the speed will be too.

As the researchers explain in this week’s issue of Nature (abstract) this was the only example of such emission in a sample of 30 ‘Class 0 protostars’ – the youngest type of young stellar objects. The embryonic star system is about 1,000 light years away in the Perseus constellation and is named NGC 1333-IRAS 4B.

Image: artist’s concept of fledgling solar system / NASA/JPL-Caltech