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Where in the Galaxy, and how long ago, did 3I/ATLAS form?

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

Where it stands

Two answers have been proposed. None is ahead on the evidence yet. Two are still possible.

Why it matters

Its speed and isotopes have been read as a body from the Galaxy's old thick disc, older than the Sun, or as a thin-disc object a few billion years old. The answer says whether planets were forming around the first metal-poor stars.

Answers 2

A thin-disc body a few billion years old
Evidence for it, no test yet
Evidence: 2 for
Still possible
An old thick-disc body, older than the Sun
Evidence for it, no test yet
Evidence: 2 for
Still possible

Next steps 1

1
Repeat the stellar traceback with Gaia DR4
Could shiftFair odds~24 h
9score
Details

When Gaia DR4 is released, rerun the backward integration with its larger catalogue and better velocities. A membership probability that moves decisively to thick or thin disc settles which answer leads; a home star within a few parsecs would be a first.

Ranked by how likely each is to move the key question, for the time it takes

History

  1. Kakharov & Loeb: population model: older than 7.6 billion yearsFor: An old thick-disc body, older than the Sun
  2. Hopkins et al.: population model: older than 7.6 billion yearsFor: An old thick-disc body, older than the Sun
  3. Eubanks et al.: population model: older than 7.6 billion yearsFor: An old thick-disc body, older than the Sun
  4. Guo et al.: gaia traceback favours the thin disc and finds no home starFor: A thin-disc body a few billion years old
  5. Pérez-Couto et al.: gaia traceback favours the thin disc and finds no home starFor: A thin-disc body a few billion years old
  6. Taylor & Seligman: kinematic age of 3 to 11 billion yearsFor: A thin-disc body a few billion years old
  7. Cordiner et al.: carbon isotopes date the ices to 10 to 12 billion years agoFor: An old thick-disc body, older than the Sun
  8. Sky & Telescope: carbon isotopes date the ices to 10 to 12 billion years agoFor: An old thick-disc body, older than the Sun
  9. Barry-Taylor: kinematic age of 3 to 11 billion yearsFor: A thin-disc body a few billion years old
  10. Session 1: raised the question, proposed two answers and found four results bearing on its answers
Add evidence
1What it bears on2What you found3Where it comes from
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