SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in 3I/ATLAS
2025/08/21 by C. M. Lisse, Lisse, C. M., Y. P. Bach +37 · 7 voices · 13 citations
#astro-ph.EP #astro-ph.GA #astro-ph.SR #gr-qc
paper · pdf · doi:10.48550/arxiv.2508.15469
Abstract
In mid-August 2025, 0.75-5.0 micron SPHEREx imaging spectrophotometric and ancillary NASA-IRTF SpeX 0.7-2.5 micron low-resolution spectral observations of Interstellar Object 3I ATLAS were obtained. The combined spectrophotometry is dominated by features due to water ice absorption and CO2 gas emission. A bright, 3 arcmin radius CO2 gas coma was clearly resolved, corresponding to Qgas,CO2 = 9.4 x 1026 molec/sec. From the SPHEREx photometry, we put conservative, preliminary 3sigma upper limits on the gas production rates for H2O and CO of 1.5 x 1026 and 2.8 x 1026 molec/sec. No obvious jet, tail, or trail structures were found in SPHEREx images. Assuming all observed 1-um flux is scattered light from an pv = 0.04 albedo spherical nucleus, its radius would be 23 km. Compared to the nucleus size limit r = 2.8km of Jewitt+ 2025, this suggests that greater than 99 percent of the measured SPHEREx continuum flux is from coma dust.
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Discussions
- Not as exciting as aliens, but if you want to see how actual planetary scientists study interstellar objects like 3I/ATLAS, this new paper just dropped on arxiv arxiv.org/pdf/2508.15469. The SPHEREx a [bsky, 104 points, 3 comments]
- I'd forgotten about SPHEREx, but this new paper seems to support that the Swift OH detection is probably not real, with a far lower upper limit on water: arxiv.org/abs/2508.15469 Pretty convincing CO2 [bsky, 6 points, 2 comments]
- Discovery of Strong Water Ice Absorption, Extended Carbon Dioxide Coma-3I/Atlas [hn, 2 points, 0 comments]
- Today on the #arXiv : Lisse et al. 2025, "SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in #3I/ATLAS" - arxiv.org/abs/2508.15469 As expected for the comet. [bsky, 2 points, 0 comments]
- Here's the SPHEREx preprint paper: arxiv.org/abs/2508.15469 (A little historical note: I worked with the lead author, Lisse, on the Deep Impact project over 20 years ago. That was a fun mission.) [bsky, 1 points, 1 comments]
- @mbkplus.bsky.social am I reading this preprint correctly that the latest observations indicate that 3I/ATLAS is a 46km object? Weren’t the prior observations that it was ~1km? arxiv.org/pdf/2508.1546 [bsky, 1 points, 1 comments]
- Today on the # arXiv : Lisse et al. 2025, "SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in # 3I /ATLAS" - https:// arxiv.org/abs/2508.15469 As expected for the [mastodon, 0 points, 0 comments]
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