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What shape was 'Oumuamua, and how did it spin?

Asked 26 Oct 2026 by ·Part of What was 'Oumuamua made of?·3 answers·0·0 following
Three answers, none aheadNone is ahead yet. See what would settle it.

Where it stands

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

Why it matters

The brightness range of about 2.5 magnitudes is the largest of any small body, and the shape bears directly on the acceleration readings: radiation pressure depends on area, outgassing torques on geometry⁠[1]⁠[2]. The light curve allows two very different shapes⁠[3].

Answers 3

Evidence: 2 for, 1 against
Still possible
Evidence: 3 for
Still possible
None of these.
Not tested enough to call either way
Evidence: none yet
Still possible

History

  1. Meech et al. puts forward: a long, thin cigar (axis ratio about 1:8 or more) tumbling near its lowest rotational energy state.
  2. Meech et al.: a 2.5-magnitude range implies a body about ten times longer than wide.For: A long, thin cigar (axis ratio about 1:8 or more) tumbling near its lowest rotational energy state.
  3. Belton et al. puts forward: a thin flattened disc (about 1:6) tumbling near its highest rotational energy state.
  4. Fraser et al.: the body tumbles, with an axis ratio of at least 5:1.For: A long, thin cigar (axis ratio about 1:8 or more) tumbling near its lowest rotational energy state.
  5. Belton et al.: the spin data fit either a cigar or a very flat spheroid and cannot separate them.For: A thin flattened disc (about 1:6) tumbling near its highest rotational energy state.
  6. Mashchenko: a cigar of about 1:8 fits but is less probable than a disc (16 against 91 per cent) from the depth of the…Against: A long, thin cigar (axis ratio about 1:8 or more) tumbling near its lowest rotational energy state.
  7. Mashchenko: physical light-curve modelling favours the disc.For: A thin flattened disc (about 1:6) tumbling near its highest rotational energy state.
  8. Seligman & Laughlin: sublimation of a volatile ice drives the axis ratio to extreme values.For: A thin flattened disc (about 1:6) tumbling near its highest rotational energy state.
  9. Asked on this site
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