Indications of Rapid Dust Formation in the Inner Region of a Protoplanetary Disk

Abstract We report a significant increase in mid-infrared emission ≤10 μ m in a transitional disk. The 2024 JWST/MIRI observation of the disk around CVSO 1942 reveals flux increase by a factor of 2 at λ ≤10 μ m, compared to the near-photospheric flux level observed with Spitzer's Infrared Spectrograph (IRS) in 2005. No significant change in flux at ≳15 μ m is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this ≤10 μ m flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1400 K), optically thick, large (≳1 μ m) dust grains near the dust sublimation radius. We propose that this rapid dust appearance may indicate in situ dust formation, possibly from planetesimal collisions in the inner disk.