제목: 3I/ATLAS: Insights from SPHEREx and Polarimetric Observations​​

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​​​​​​​​​​​​​​​​​​연사: Dr. Yoonsoo Bach (KASI)​

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일시: 2026년 4월 24일 금요일 11:00

장소: 과학관 B101호​​​

Abstract:

​3I/ATLAS, the third known interstellar object, was discovered in July 2025. SPHEREx began science operations in May 2025 and quickly initiated special observations prior to 3I’s perihelion. These August 2025 observations led to the first detection of an extended CO2 gas coma (4.25 um; Lisse, Bach et al. 2025, 2026), about one week before independent JWST results (Cordiner et al. 2025). The initially low CO/CO2 gas ratio, among the lowest observed in comets, reversed dramatically after perihelion, with the emergence of a large CO gas coma. This behavior is consistent with significant water production (Combi et al. 2026, ApJL), which likely led to excavation of several meters of surface material and exposure of fresh volatile ices. Optical to NIR polarimetry of the dust coma (Choi et al. 2026) shows a polarization phase curve unlike any solar system object, but with wavelength dependence similar to solar system comets, suggesting a distinct bulk composition but similar dust microstructure. Together, these results indicate that 3I is compositionally alien yet structurally familiar. I will present recent results and discuss implications for interstellar object science.​