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Why did 3I/ATLAS's activity and chemistry change so much across perihelion?

Asked 2 Nov 2026 by ·1 answer·0·0 following
One answer, none aheadNone is ahead yet. See what would settle it.

Where it stands

One answer has been proposed. None is ahead on the evidence yet. One is still possible. Of the one narrower question under it, none is answered yet.

Why it matters

Inbound it was a CO2-dominated coma with little water; near and after perihelion water and then CO took over, methane appeared late, and reported water rates differ tenfold. What changed tells us how the body is layered.

Answers 1

Evidence: 2 for
Still possible

History

  1. Lisse et al.: water took over near perihelion; the ice band vanishedFor: Heat reached deeper, water-richer layers and icy grains
  2. Luco et al.: water took over near perihelion; the ice band vanishedFor: Heat reached deeper, water-richer layers and icy grains
  3. Belyakov et al.: CO most abundant by December; methane appears lateFor: Heat reached deeper, water-richer layers and icy grains
  4. Roth et al.: CO most abundant by December; methane appears lateFor: Heat reached deeper, water-richer layers and icy grains
  5. Session 1: raised the question, proposed one answer, found two results bearing on its answers and worked on one of its sub-questions
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