An artist's concept of the snow line in TW Hydrae showing water ice covered dust grains in the inner disc (4.5–30 astronomical units, blue) and carbon monoxide ice covered grains in the outer disc (>30 astronomical units, green). The transition from blue to green marks the carbon monoxide snow line. The snow helps grains of dust to adhere to each other by providing a sticky coating, which is essential to the formation of planets and comets. Due to the different freezing points of different chemical compounds, different snow lines can be found at various distances from the star.
This ALMA image shows the region where carbon monoxide snow has formed around the star. The carbon monoxide is shown here in green, and begins at a distance of more than 30 astronomical units from TW Hydrae. Aside from being necessary for planetary and comet formation, carbon monoxide is needed for the creation of methanol which is a fundamental building block required for life.
Credit: (top) B. Saxton & A. Angelich/NRAO/AUI/NSF/ALMA (ESO/NAOJ/NRAO); (bottom) ALMA (ESO/NAOJ/NRAO)
Note: For more information, see Snow in an Infant Planetary System.