2026-04-16 カリフォルニア工科大学（Caltech）
These observations by NASA’s SPHEREx show the infrared light emitted by the dust, water, organic molecules, and carbon dioxide contained within comet 3I/ATLAS’s coma during the mission’s December 2025 campaign.Credit: NASA/JPL-Caltech
＜関連情報＞
- https://www.caltech.edu/about/news/interstellar-comet-reveals-methane-on-its-journey-through-our-solar-system
- https://iopscience.iop.org/article/10.3847/2041-8213/ae5700
JWST/MIRIで観測された3I/ATLASの揮発性物質の分布 The Volatile Inventory of 3I/ATLAS as Seen with JWST/MIRI
Matthew Belyakov, Ian Wong, Bryce T. Bolin, M. Ryleigh Davis, Steven J. Bromley, Carey M. Lisse, and Michael E. Brown
The Astrophysical Journal Letters Published: 2026 April 8
DOI:10.3847/2041-8213/ae5700
Abstract
We present the first spectroscopic characterization of an interstellar object at mid-infrared wavelengths. Postperihelion observations of 3I/ATLAS (3I) using the JWST/MIRI medium-resolution spectrometer were obtained on 2025 December 15–16 and 27, when the object was at heliocentric distances of 2.20 and 2.54 au, respectively. Our 5–28 μm spectra exhibit fluorescence features from several gaseous species, including the ν2 band of H2O at 5.8–7.0 μm, the primary ν2 and associated hot bands of CO2 around 15 μm, and a forbidden transition of atomic nickel at 7.507 μm. We also report the first direct detection of CH4 in an interstellar object. The sharp rise in CH4 production relative to H2O suggests past CH4 depletion from the outermost layers, with the observed CH4 emerging from unprocessed subsurface material. Comparison of the volatile production rates measured during the two epochs indicates a significant reduction in the overall outgassing over 12 days, with the measured H2O activity level dropping more steeply than other species. As shown through near-nucleus coma mapping, 3I continues to display an extended source of H2O production from icy grains entrained within the coma. Our production rate measurements confirm that 3I has a strongly enhanced CO2:H2O mixing ratio relative to typical solar system comets, as well as a somewhat enriched CH4:H2O value.
