SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in 3I/ATLAS
Abstract In mid-August 2025, 0.75–5.0 μ m SPHEREx imaging spectrophotometric and ancillary NASA-IRTF/SpeX 0.7–2.5 μ m low-resolution spectral observations of 3I/ATLAS were obtained. The combined spectrophotometry is dominated by features due to water ice absorption and CO 2 gas emission. A bright, ∼3′ radius CO 2 gas coma was clearly resolved, corresponding to Q gas,CO2 ∼9.4 × 10 26 molecules s −1 . From the SPHEREx photometry, we put conservative, preliminary 3 σ upper limits on the gas production rates for H 2 O and CO of 1.5 × 10 26 and 2.8 × 10 26 molecules s −1 , respectively. No obvious jet, tail, or trail structures were found in SPHEREx images. If we assume all observed 1 μ m flux is scattered light from a p v = 0.04 albedo spherical nucleus, then the radius would be R nuc ∼ 23 km. Given the nucleus size limit R nuc < 2.8 km from D. Jewitt et al., we conclude >99% of the measured SPHEREx continuum flux is from coma dust.
Authors
- Sean Bryan (ORCID: https://orcid.org/0000-0003-4607-9562)
- Volker Tolls (ORCID: https://orcid.org/0000-0003-1841-2241)
- Joshua P. Emery (ORCID: https://orcid.org/0000-0001-9265-9475)
- Gary J. Melnick (ORCID: https://orcid.org/0000-0002-6025-0680)
- Olivier Doré (ORCID: https://orcid.org/0000-0001-7432-2932)
- Phillip Korngut (ORCID: https://orcid.org/0009-0003-8869-3365)
- B. P. Crill (ORCID: https://orcid.org/0000-0002-4650-8518)
- Zafar Rustamkulov (ORCID: https://orcid.org/0000-0003-4408-0463)
- Beth Fabinsky
- A. Cukierman (ORCID: https://orcid.org/0000-0002-7471-719X)
- Bo Yang (ORCID: https://orcid.org/0000-0002-5453-0707)
- C. M. Lisse (ORCID: https://orcid.org/0000-0002-9548-1526)
- M. W. Werner (ORCID: https://orcid.org/0000-0003-4990-189X)
- Michael L. Sitko (ORCID: https://orcid.org/0000-0003-1799-1755)
- Michael S. Connelley (ORCID: https://orcid.org/0000-0002-8293-1428)
- Y. R. Fernández (ORCID: https://orcid.org/0000-0003-1156-9721)
- Andreas L. Faisst (ORCID: https://orcid.org/0000-0002-9382-9832)
- Yoonsoo P. Bach (ORCID: https://orcid.org/0000-0002-2618-1124)
- Chansey Champagne (ORCID: https://orcid.org/0009-0001-1093-3715)
Institutions
- University of Central Florida (US)
- California Institute of Technology (US)
- Space Science Institute (US)
- Planetary Science Institute (US)
- Jet Propulsion Laboratory (US)
- Northern Arizona University (US)
- Korea Astronomy and Space Science Institute (KR)
- Johns Hopkins University Applied Physics Laboratory (US)
- University of Hawaii at Hilo (US)
- Center for Astrophysics Harvard & Smithsonian (US)
- Infrared Processing and Analysis Center (US)
- Arizona State University (US)
Publication Details
- Journal
- Research Notes of the AAS
- Published
- 2025-09-09
- DOI
- https://doi.org/10.3847/2515-5172/ae0293
- Citations
- 16
- Primary Topic
- Atmospheric Ozone and Climate
- Type
- article
- Field-Weighted Citation Impact
- 20.81