A 'snow line' in the gas-rich disk around a young star shows how far from the star carbon monoxide freezes, and so where planets are likely to form. Carbon monoxide ice indicates that temperatures are cold enough for the chemical components of planets to form. It also increases the density of dust grains and helps them to clump together. A team led by Chunhua Qi of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and Karin Öberg of the University of Virginia in Charlottesville studied the gas disk surrounding TW Hydrae, a star 54 parsecs from Earth. This revealed signals of diazenylium, an ion that exists mainly in areas where carbon monoxide is frozen. The team found this snow line about 30 Earth–Sun distances from the star. Knowing the location could help astronomers to shape models of planet formation in the Solar System and beyond, the authors say.

Science http://dx.doi.org/10.1126/science.1239560 (2013)