The structure of the water ice also pointed in this direction. When water freezes at moderate temperatures, its molecules arrange themselves into an ordered crystal lattice, and crystalline ice produces a sharp peak in the spectrum just above 3 micrometers. This peak was missing from Beta Pictoris. The ice is almost entirely amorphous, a disordered, glass-like solid formed when water molecules freeze so quickly and so cold that they stick wherever they land. The team estimates that less than 7 percent of the water ice in the system is crystalline, which is somewhat surprising.
Models predicted that the ice in debris disks should be mostly crystalline. For amorphous ice to remain in this form, it must remain colder than about 100 Kelvin, or minus 173° Celsius. Otherwise, the crystal structure must be constantly being broken up by something, such as high-energy ultraviolet light, cosmic rays, or particles emanating from the star. Whatever the case, the researchers concluded that the ice most likely formed in the interstellar medium long before the planets of Beta Pictoris took shape.
The remaining question was how the ice grains were distributed so evenly across the disk.
Constant collisions
The team argues that this even distribution of ice requires frequent collisions between planetesimals. Each collision would release new ice dust, including ice that was buried and protected deep within the colliding bodies, replenishing what destroys starlight. We already have evidence that such collisions occur. Previous infrared images showed a curved, sloping streak of dust in the disk’s southwestern arm, thought to be debris from a violent collision slightly less than halfway up the star.
Betti’s team’s findings support the idea that the disk’s carbon monoxide gas comes from colliding icy bodies and offer an explanation for how ice can survive in an environment constantly exposed to ultraviolet light. However, the team couldn’t determine exactly how much crystalline ice is present or rule out other molecules hidden in the mix.
But if a young planetary system 64 light-years away began with the same icy components as ours, then ancient interstellar ice could be a common component of planetary systems in general. This means that the raw materials for water-rich, potentially habitable worlds could also be common.
Science, 2026. DOI: 10.1126/science.adw7770
