Artist concept of the so-called “snow line” in the young planet-forming system known as TW Hydrae. A snow line is where particles become icy and can more easily stick together to make larger chunks when they collide. This is one way for planets to form. ALMA has found water-covered ice grains in this system’s inner disk (4.5 — 30 AU, blue) and carbon monoxide (CO) ice-covered grains in the outer disk (>30 AU, green). The transition from blue to green marks the CO snow line.
Credit: Alexandra Angelich and Bill Saxton (NRAO/AUI/NSF)