Overview
- A new Hubble–Keck–Gemini modeling study posted Oct. 22 explains the sunward anti‑tail as sunlight scattering from water‑ice grains ejected by CO2 sublimation, with scattering peaking at 3–4 AU before a transition to a conventional tail.
- Independent Oct. 22 photometry from the Nordic Optical Telescope finds a heliocentric power‑law index of n ≈ 3.8 and dust production consistent with CO2‑driven activity, with morphology evolving from a sunward fan to an antisolar tail as larger, slow dust responds to radiation pressure.
- Earth‑based views are now largely blocked after the object reached solar conjunction on Oct. 21; perihelion occurs on Oct. 29, constraining monitoring during its closest approach to the Sun.
- A preprint accepted by Research Notes of the AAS outlines late‑October to early‑November opportunities for Hera (Oct. 25–Nov. 1) and Europa Clipper (Oct. 30–Nov. 6) to pass downwind of the ion tail, with Europa Clipper carrying suitable plasma and magnetometer instruments.
- Earlier Keck spectroscopy reported cyanide and nickel emissions, including components directed sunward, supporting the anti‑tail interpretation, while most researchers continue to assess 3I/ATLAS as a natural comet.