YSES-1 b is the inner companion, orbiting at 146 AU (2.18×1010 km; 1.36×1010 mi) from the host star, or slightly more than 5 times theNeptune-Sun distance.[11] Its mass has been estimated to be14MJ,[8] though another estimate give21.8MJ. This mass is higher than the generally-used deuterium burning limit of13MJ, which is often used to separate planets from brown dwarfs.[9] In July 2021, astronomers reported the detection, for the first time, of anisotope in theatmosphere of anexoplanet; more specifically, the isotopeCarbon-13 (C13) was found in the atmosphere.[13][14] This was later confirmed withVLT/CRIRES+. This spectrum showed that the atmosphere is dominated bywater vapor andcarbon monoxide. The researchers also detecthydrogen fluoride in the atmosphere. The object is anL-dwarf with a spectral type of L0.[15] Observations with theJames Webb Space Telescope detectedsilicate emission from YSES-1b, indicating the presence of acircumplanetary disk. The emission was attributed tosubmicronolivine dust grains. These very small and hot grains might have formed from collisions of satellites forming inside the circumplanetary disk.[12] Observations with VLTMUSE revealed emission byhydrogen (Hα,Hβ),calcium (H+K lines) andhelium, coming from YSES 1b. These lines are attributed to accretion of material from the circumplanetary disk to the surface of the planet. It is the first object in this mass range with this full combination of lines. The planet accretes between 1.11 x 10-9±0.19MJ/yr and 1.45 x 10-9±0.19MJ/yr (or the mass equivalent of at least21 Lutetia per year).[16]
YSES-1 c is a body with a mass of7.2MJ, and orbits at 320 AU (4.8×1010 km; 3.0×1010 mi), or slightly more than 11 times the Neptune-Sun distance.[5][9] Atmospheric water vapor and carbon monoxide was detected with VLT/CRIRES+. The object is an L-dwarf with a spectral type of L7.5.[15] AdditionallyJWST spectra withNIRSpec andMIRI were published. The spectrum of TYC 8998-760-1 c does show direct detection ofsilicate clouds.[17][12]
^Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars".Astronomy and Astrophysics.355:L27 –L30.Bibcode:2000A&A...355L..27H.
^abcdRoberts, Jonathan; Thompson, William; Wang, Jason J.; Blunt, Sarah; Balmer, William O.; Bourdarot, Guillaume; Bowler, Brendan P.; Chauvin, Gael; Eisenhauer, Frank; Henning, Thomas K.; Kammerer, Jens; Kiefer, Flavien; Kenworthy, Matthew A.; Kervella, Pierre; Lacour, Sylvestre; Lagrange, A. -M.; Nielsen, Eric L.; Pueyo, Laurent; Rickman, Emily; Sipilä, Olli; Spezzano, Silvia; Stolker, Tomas; Zurlo, Alice (2025). "New Orbital Constraints for YSES 1 b and HR 2562 B from High-Precision Astrometry and Planetary Radial Velocities".arXiv:2509.14321 [astro-ph.EP].
^abcdHoch, K. K. W.; Rowland, M.; Petrus, S.; Nasedkin, E.; Ingebretsen, C.; Kammerer, J.; Perrin, M.; d'Orazi, V.; Balmer, W. O.; Barman, T.; Bonnefoy, M.; Chauvin, G.; Chen, C.; De Rosa, R. J.; Girard, J.; Gonzales, E.; Kenworthy, M.; Konopacky, Q. M.; MacIntosh, B.; Moran, S. E.; Morley, C. V.; Palma-Bifani, P.; Pueyo, L.; Ren, B.; Rickman, E.; Ruffio, J.-B.; Theissen, C. A.; Ward-Duong, K.; Zhang, Y. (2025). "Silicate clouds and a circumplanetary disk in the YSES-1 exoplanet system".Nature.643 (8073):938–942.arXiv:2507.18861.Bibcode:2025Natur.643..938H.doi:10.1038/s41586-025-09174-w.PMID40494394.
^Julo, R.; Bonnefoy, M.; Chatelain, F.; Flasseur, O.; Michel, O. J. J.; Jorquera, S.; Delorme, P.; Chauvin, G. (2025). "Stellar halo subtraction alternative for accreting companions' characterization with integral field spectroscopy: Analytical and on-sky demonstration on the PDS70, HTLup, and YSES1 systems".arXiv:2509.09878 [astro-ph.IM].
^Hoch, Kielan; Perrin, Marshall; Ruffio, Jean-Baptiste; Theissen, Christopher; Barman, Travis; Konopacky, Quinn; Kammerer, Jens; Rickman, Emily; Balmer, William; Pueyo, Laurent; Macintosh, Bruce; Ren, Bin; Morley, Caroline; Gonzales, Eileen; Petrus, Simon (2024-04-01). "Direct Imaging Spectroscopy of Substellar Companions with JWST".AASTCS10, Extreme Solar Systems V, Bulletin of the American Astronomical Society.56 (4): 626.13.Bibcode:2024ESS.....562613H.
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