A Tale of Two Dust Disks in Our Milky Way

Abstract Cosmic dust plays a vital role in stellar and galactic formation and evolution, but its three-dimensional structure in the Milky Way has remained unclear due to insufficiently precise reddening and distance measurements. Although early studies typically adopted a single-disk model, we detect two distinct components at Galactocentric distances of 5–14 kpc, enabled by photometric, spectroscopic, and astrometric measurements of over 5 million stars. The thin dust disk’s scale height increases radially from 60 to 200 pc, while the thick disk grows from 300 to 800 pc. For the first time, we find the thin and thick dust disks correlate spatially with the molecular and atomic hydrogen disks, respectively. The thin, thick, and combined disks have scale lengths of 9 . 6 − 1.1 + 1.2 , 4 . 2 − 0.3 + 0.4 , and 6 . 6 − 0.3 + 0.3 kpc, respectively. The gas-to-dust ratio shows an exponential radial gradient, increasing from ∼60 at 5 kpc to ∼470 at 14 kpc. These findings provide new insights into dust morphology in the Galaxy and raise fundamental questions that require further investigation.