The dust around the young star CVSO 1942 flared up like a light bulb switched to full power. In 2024, the James Webb Space Telescope (JWST) peered into a transitional disk, a ring of gas and dust where planets are still being built, and saw that in mid-infrared light (wavelengths shorter than 10 micrometers, about ten times thinner than a human hair) the disk had become twice as bright as it was in 2005, when the old Spitzer telescope observed it. And not everything flared at once: at longer wavelengths, from 15 micrometers and beyond, the brightness remained the same.
Comparing the new images with data from the NEOWISE infrared sky survey, astronomers realized the brightness increase happened in just two weeks. Such speed suggests the dust did not arrive from afar but was born right on the spot — hot, around 1400 kelvins (a bit hotter than lava in a volcano's throat), dense, made of large grains larger than a micron. They gathered at the line where the star's heat evaporates dust, like droplets condensing at the edge of a hot pan.
The most likely explanation is a collision of planetesimals — planetary embryos the size of asteroids. The impact shattered them into a cloud of debris, and that cloud heated up and glowed in the infrared within a couple of weeks. For astronomers, this is a rare stroke of luck: witnessing the birth of dust that will later assemble into new planets. Until now, such flares were mostly caught around old stars, but here it's a young star, where everything is just beginning.
as written by the authors arXiv:2602.08973
We report a significant increase in mid-infrared emission $$\leq10$$ $$\mu$$m in a transitional disk. The 2024 JWST/MIRI observation of the disk around CVSO 1942 reveals flux increase by a factor of two at $$\lambda\leq10$$ $$\mu$$m, compared to the near photospheric flux level observed with Spitzer/IRS in 2005. No significant change in flux at $$\gtrsim15$$ $$\mu$$m is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this $$\leq10$$ $$\mu$$m flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1,400 K), optically thick, large ($$\gtrsim1$$ $$\mu$$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.
The dust temperature of 1400 kelvins is exactly the boundary where rock starts to melt. A bit closer to the star, and the dust grains would have evaporated like snow in the sun.