The "snow line" -- the point where carbon monoxide freezes in the disk around a sunlike star -- may give researchers more clues on how planets form. A team of astronomers calculating the snow line for the star TW Hydrae found that carbon monoxide freezes at about the distance of the orbit of Neptune. "The CO snow line is interesting, not only because CO is abundant in the disks, but its snow line is the most accessible to direct observations due to its low freeze-out temperature. ... It could mark the starting point where smaller icy bodies ... would begin to form," said Chunhua Qi of the Harvard-Smithsonian Center for Astrophysics.