articlePublications of the Astronomical Society of the PacificJan 1, 2026HYBRID OA

Rapid Brightening of 3I/ATLAS Ahead of Perihelion

QZQicheng ZhangKBKarl Battams

Lowell Observatory · United States Naval Research Laboratory

Indexed inarxivcrossref

Abstract

Abstract Interstellar comet 3I/ATLAS has been approaching its 2025 October 29 perihelion while opposite the Sun from Earth, hindering ground-based optical observations over the preceding month. However, this geometry placed the comet within the fields of view of several space-based solar coronagraphs and heliospheric imagers, enabling its continued observation during its final approach toward perihelion. We report photometry from STEREO-A’s SECCHI HI1 and COR2, SOHO’s LASCO C3, and GOES-19’s CCOR-1 instruments in 2025 September–October, which show a rapid rise in the comet’s brightness scaling with heliocentric distance r as r −7.5±1.0 . CCOR-1 also resolves the comet as an extended source with an apparent…

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Topics & keywords

Topics
Keywords
  • Photometry (optics)
  • Brightness
  • Comet
  • Comet dust
  • Solar System
  • Comet tail
  • Coma (optics)
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