dorsal/arxiv
View SchemaSPHEREx Re-Observation of Interstellar Object 3I/ATLAS in December 2025: Detection of Increased Post-Perihelion Activity, Refractory Coma Dust, and New Coma Gas Species
| Authors | C. M. Lisse, YP. Bach, S. A. Bryan, P. M. Korngut, B. P. Crill, A. J. Cukierman, O. Doré, A. Cooray, B. Fabinsky, A. L. Faisst, H. Hui, G. J. Melnick, C. H. Nguyen, Z. Rustamkulov, V. Tolls, M. W. Werner |
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| Categories | |
| ArXiv ID | 2601.06759vv1 |
| URL | https://arxiv.org/abs/2601.06759 |
| License | http://creativecommons.org/licenses/by/4.0/ |
Abstract
In December-2025, the NASA SPHEREx spacecraft re-observed ISO 3I/ATLAS post-perihelion, finding a much more active object compared to August-2025 SPHEREx pre-perihelion observations, with marked evidence for development into an cometary body fully sublimating all its ices. The new imaging spectrophotometry is dominated by spatially resolved features due to dust scattered-light and thermal emission plus gas-emissions from CN (0.93 um), H2O (2.7 um), organic C-H (3.2 to 3.6 um), CO2 (4.25 to 4.27 um), and CO (4.6 to 4.8 um). The CO2 gas-coma continues to be extended out to a 3 arcmin radius. The continuum spectral signature of H2O-ice absorption has mostly disappeared, replaced by scattered-light plus thermal-emission from organo-silicaceous dust grains while the H2O gas-emission is 20 times brighter. All but the organics-gas comae are circularly symmetric, while a weak pear-shaped solar-pointing dust tail consistent with large dust grains is now present. The new appearance of CN and C-H features suggests that these species are contained either in H2O phases or were trapped under them.
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"abstract": "In December-2025, the NASA SPHEREx spacecraft re-observed ISO 3I/ATLAS post-perihelion, finding a much more active object compared to August-2025 SPHEREx pre-perihelion observations, with marked evidence for development into an cometary body fully sublimating all its ices. The new imaging spectrophotometry is dominated by spatially resolved features due to dust scattered-light and thermal emission plus gas-emissions from CN (0.93 um), H2O (2.7 um), organic C-H (3.2 to 3.6 um), CO2 (4.25 to 4.27 um), and CO (4.6 to 4.8 um). The CO2 gas-coma continues to be extended out to a 3 arcmin radius. The continuum spectral signature of H2O-ice absorption has mostly disappeared, replaced by scattered-light plus thermal-emission from organo-silicaceous dust grains while the H2O gas-emission is 20 times brighter. All but the organics-gas comae are circularly symmetric, while a weak pear-shaped solar-pointing dust tail consistent with large dust grains is now present. The new appearance of CN and C-H features suggests that these species are contained either in H2O phases or were trapped under them.",
"arxiv_id": "2601.06759",
"authors": [
"C. M. Lisse",
"YP. Bach",
"S. A. Bryan",
"P. M. Korngut",
"B. P. Crill",
"A. J. Cukierman",
"O. Dor\u00e9",
"A. Cooray",
"B. Fabinsky",
"A. L. Faisst",
"H. Hui",
"G. J. Melnick",
"C. H. Nguyen",
"Z. Rustamkulov",
"V. Tolls",
"M. W. Werner"
],
"categories": [
"astro-ph.EP",
"astro-ph.GA",
"astro-ph.SR"
],
"license": "http://creativecommons.org/licenses/by/4.0/",
"title": "SPHEREx Re-Observation of Interstellar Object 3I/ATLAS in December 2025: Detection of Increased Post-Perihelion Activity, Refractory Coma Dust, and New Coma Gas Species",
"url": "https://arxiv.org/abs/2601.06759",
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