Speaker
Description
3I/ATLAS is the second known comet of extrasolar origin. It was discovered on 1 July 2025, and immediately attracted the attention of many observers. Studying its composition and evolution lets us probe the solid-body formation in other planetary systems. Using the DDT time at SALT we observed 3I/ATLAS with the RSS spectrograph on 15 and 29 July 2025. Both spectra were acquired in the wavelength range 0.36–0.74 μm. To remove the solar continuum and derive the comet’s reflectance spectrum, we observed the solar analog stars on the same nights. The 15 July spectrum shows a slope of 21.1 ± 0.2 %/μm, which is an increase from the 17.1 ± 0.2 %/μm slope observed by Seligman et al. (arXiv: 2507.02757) on 4 July. This change of reddening over time suggests an evolving surface or coma composition. The 29 July data, obtained when the comet was closer to the Sun, show a genuine CN (B²Σ⁺ – X²Σ⁺) violet-band emission. Other molecular or atomic bands (e.g., C₃, C₂, CO⁺) show no clear excess above the reflected continuum. These Target of Opportunity observations of 3I/ATLAS demonstrate SALT’s rapid response capabilities that will be essential for following up discoveries from the Vera C. Rubin Observatory (LSST) in the coming years.
| Stream | Science or Engineering |
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