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Description
Circumstellar discs, a natural byproduct of the formation of low-mass stars and substellar objects, are crucial in setting the conditions and timescale for planet formation. These discs have been observed around free-floating planetary-mass objects (FFPMOs) at young ages. We present the near- and mid-infrared spectra of eight young FFPMOs with masses of 5–10 MJup, obtained using the NIRSpec and MIRI instruments on the James Webb Space Telescope. The photospheric spectra of our targets show a clear diversity at similar temperatures, especially in the 3-5 $\mu$m range, unaccounted for by existing atmospheric models. We find silicate absorption feature in the photosphere of one of our targets, the first such detection in very young FFPMOs, indicating silicate clouds in their cool atmospheres. Additionally, six objects show mid-infrared excess emission above the photosphere, as well as silicate emission features, demonstrating the presence of discs. The shape and strength of the latter features constitute strong evidence of grain growth and crystallisation, akin to that observed in discs around higher-mass brown dwarfs and stars. We also detect emission lines from hydrocarbon molecules in the disks of several targets and a multi-epoch study of one of them shows an ongoing accretion burst (see Jayawardhana et al. contribution). The presence and characteristics of discs point to the potential for the formation of rocky companions around FFPMOs.
