A Dust Ring Where Giants Are Born express
Around the young star MWC 480, a flat disk of gas and dust whirls, like a giant carousel where, instead of horses, you have building blocks for planets. Radio telescopes peered into this disk at different wavelengths, from millimeter to centimeter, and saw exactly where the dust accumulates and how large the grains are.
The brightest ring sits at 95 astronomical units from the star — about three times farther out than Neptune is from the Sun. For the first time, it was spotted at a wavelength of 9.1 millimeters. Inside the ring, dust grains stick together into clumps up to a centimeter in size, like snowballs gradually building a snowman. The mass of this ring alone is between 43 and 100 Earth masses. That's enough to assemble the cores of giant planets like Jupiter.
Observations at different wavelengths showed that the dust in the ring comes in two varieties: dense, compact grains or very porous ones, 90% empty space, like a sponge. Both options explain the data equally well. To choose between them, we need even broader observations, and then we'll understand more precisely what planets are made of.
The ring at 95 astronomical units is not just a storage depot. Its sharp edges and constant width across all wavelengths suggest that assembly of large bodies may already be underway inside. And a bit farther out, at 160 astronomical units, lurks a second, fainter ring, like the outer asteroid belt in our system, but around another star.
Original abstract
as written by the authors arXiv:2602.19941
We present deep, high-resolution ($$\sim$$100 mas) Karl G. Jansky Very Large Array (VLA) Ka-band (9.1 mm) observations of the disk around MWC 480, and infer dust properties through a combined analysis with archival Atacama Large Millimeter/submillimeter Array (ALMA) data at 0.87, 1.17, 1.33, and 3.0 mm. The prominent dust ring at 95 au (B95) is detected at 9.1 mm for the first time, while the faint outer ring at 160 au is not revealed. Through non-parametric visibility modeling, we identified two new annular features: a plateau within 20-50 au across all wavelengths, and a shoulder exterior to the B95 ring at 0.87, 1.17 and 1.33 mm, consistent with signatures of planet-disk interaction. We find that the width of the B95 ring remains constant across wavelengths, suggesting that fragmentation dominates over radial diffusion or that unresolved substructure is present within the ring. Resolved spectral modeling yields two families of dust solutions that reproduce the observations equally well: compact grains or highly porous (90\%) grains, with carbonaceous components dominated by refractory organics or amorphous carbon, respectively. The inferred maximum grain sizes peak at the locations of the two rings and reach centimeter within the B95 ring. The total dust masses are $$860^{+95}_{-78}\rm~M_\oplus$$/$$1500^{+440}_{-330}\rm~M_\oplus$$ (large/small-grain solution in inner disk) and $$230^{+14}_{-13}\rm~M_\oplus$$ for the two dust mixtures. The B95 ring alone contains $$100^{+5}_{-5}\rm~M_\oplus$$ and $$43^{+2}_{-2}\rm~M_\oplus$$, respectively, sufficient to assemble the cores of giant planets. Finally, we highlight the power of broadband, multi-wavelength observations in placing better constraints on dust composition and porosity in protoplanetary disks.
The mass of dust in the MWC 480 ring is up to 100 Earth masses. For comparison: the entire mass of the asteroid belt between Mars and Jupiter is less than one thousandth of an Earth mass.
In Liu Cixin's novel 'The Three-Body Problem,' an alien civilization builds giant rings around a star to control its light. The dust rings around MWC 480 are a natural prototype for such structures, except instead of engineers, gravity does the work.