The James Webb Space Telescope detected ice in the debris disk around Beta Pictoris, suggesting it may have formed before the star and its planets.
The James Webb Space Telescope has detected water and carbon dioxide ice in the debris disk around Beta Pictoris, a young star about 64 light-years from Earth and roughly 20 million years old. The findings come from a study led by Sarah Betti, an astronomer at the Space Telescope Science Institute in Baltimore, published in Science.
Betti’s team observed Beta Pictoris on December 7, 2023, using Webb’s Near Infrared Spectrograph (NIRSpec), which records a full spectrum from 0.6 to 5.2 micrometers for every point in the image. After subtracting the star’s glare, the researchers measured how much starlight the disk’s dust reflects at each wavelength.
Water ice absorbs light strongly near 3 micrometers, while carbon dioxide ice absorbs at 4.27 micrometers or 4.39 micrometers when it contains the heavier carbon-13 isotope. Detailed spectra from two spots on opposite sides of the star, each roughly 100 astronomical units out, showed both water and carbon dioxide ices, including the common form and the rarer carbon-13 version.
The carbon dioxide features were shifted slightly toward shorter wavelengths and were much broader than those of pure carbon dioxide ice measured in the lab. The team says in the paper that this is how carbon dioxide behaves when its molecules are trapped inside water ice, meaning the two ices are thoroughly mixed rather than sitting side by side as separate grains.
The team calculated that there is slightly more than one carbon dioxide molecule for every 10 water molecules, meaning it is about 11 percent of the ice. That falls within the 2.5 to 30 percent range measured in Solar System comets and the 7 to 20 percent seen in the ice of disks around other newborn stars.
The water ice is almost entirely amorphous, a disordered, glass-like solid. Crystalline ice produces a sharp peak in the spectrum just above 3 micrometers, but that peak was absent at Beta Pictoris. The team estimates that less than 7 percent of the water ice in the system is crystalline.
For amorphous ice to stay in that form, it has to remain colder than about 100 Kelvin, or minus 173° Celsius. Otherwise, something has to keep breaking up its crystal structure, such as high-energy ultraviolet light, cosmic rays, or particles streaming from the star. The researchers concluded the ice most likely formed in the interstellar medium, long before the planets of Beta Pictoris began to take shape.
The team argues that the even ice distribution across the disk requires frequent collisions among planetesimals. Each collision would release fresh icy dust, including ice that had been buried and protected deep inside the colliding bodies, replenishing what the starlight destroys.
The findings support the idea that the disk’s carbon monoxide gas comes from colliding icy bodies and offer an explanation of how ice can survive in an environment constantly exposed to ultraviolet light. If a young planetary system 64 light-years away may have started with much the same icy ingredients as ours, then primordial, interstellar ice might be a common ingredient of planetary systems in general, meaning the raw materials for water-rich, potentially habitable worlds might be common, too.
Sources
This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.
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