Study Reveals Atmospheric Chemistry of Planetary-Mass Object at Planet-Brown Dwarf Boundary
A new study using high-resolution spectroscopy has measured the chemical and isotopic composition of 2MASS J0249-0557 c, a ~12 Jupiter-mass object orbiting a brown dwarf pair in the β Pictoris young moving group. The object's C/O ratio, metallicity, and carbon isotope ratio are consistent with those of benchmark brown dwarfs in the same stellar association. These findings suggest the object formed through gravitational collapse like a star, rather than through core accretion like a typical planet, despite sitting at the planet-brown dwarf boundary.
Researchers have conducted atmospheric retrieval analysis of 2MASS J0249-0557 c, a ~12 Jupiter-mass planetary-mass companion orbiting a brown dwarf binary system in the β Pictoris young moving group, using high-resolution spectroscopic data from the CRIRES+ instrument on the Very Large Telescope. The study retrieved a C/O ratio of 0.57 ± 0.01, a metallicity of [M/H] = 0.18 ± 0.05, and a ¹²CO/¹³CO isotope ratio of 95 (+23/-17), all broadly solar-like in character. Two benchmark brown dwarfs in the same moving group — 2MASSI J0443+0002 and SIPS J2000-7523 — were analyzed with the same methodology and found to have consistent compositions, enabling a homogeneous comparison. The compositional similarity between the planetary-mass companion and the brown dwarfs, combined with its wide orbital separation from its host, points toward gravitational collapse as the most likely formation mechanism rather than core accretion. The solar-like abundances of these three substellar objects now provide a reference baseline for other exoplanet members of the β Pictoris moving group, including β Pic b, 51 Eri b, and AF Lep b, whose host stellar compositions are difficult to measure directly. The authors suggest that future comparative studies of atmospheric compositions within this moving group could help distinguish between competing formation mechanisms for its planetary members.
What different sources said
- arXiv astro-phCenter
Chemistry and Isotope Ratios of Substellar Atmospheres in the $\beta$ Pictoris Young Moving Group and Vicinity
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