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NASA recently discovered 'Oumuamua, an interstellar asteroid that appears to have a very elongated shape, unseen in solar system asteroids.

oumuamua

What physical mechanisms, in the progenitor stellar system or from interstellar transit, could lead to the formation of an asteroid with such a shape?

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  • $\begingroup$ Why would it be spherical? $\endgroup$ – Rob Jeffries Nov 20 '17 at 23:53
  • $\begingroup$ No one said anything about sphericity. It is unusually elongated, I.e.it has much higher average axial ratios than asteroids in the solar system $\endgroup$ – christopherlovell Nov 20 '17 at 23:57
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    $\begingroup$ I can't help looking at the artist's conception and thinking "spaceship." $\endgroup$ – Ben Crowell Nov 21 '17 at 3:41
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    $\begingroup$ @BenCrowell You can thank Martin Kornmesser at ESA NASA HEIC for this dramatic looking image. Possibly a moment to wheel out the Flake Equation on xkcd.com. $\endgroup$ – StephenG Nov 21 '17 at 7:57
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    $\begingroup$ @BenCrowell It does seem to call to the mind the Arthur C. Clarke , Rama object. $\endgroup$ – Jeffery Thompson Nov 23 '17 at 18:27
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If you don't mind speculation, it seems to me that a massive impact - like the one that is thought to have formed our moon, but even larger, could eject shards like that. That such a shard could escape it's solar-system and fly through space between solar-systems isn't unreasonable. Asteroids (to my understanding) are somewhat loosely formed and an elongated shape like that is unlikely.

A small moon or larger asteroid near a super-nova might get turned into an elongated shape like that by the blast as another speculative answer. A 3rd possibility might be a ejection from a high velocity and somewhat violent debris disk, perhaps from a planet that fell inside the Roche limit of a white dwarf star.

It's still an object that's strange for two completely separate reasons. It being the first ever object observed to be passing through our solar-system and it's thought to be very unusual shape (footnote - better images would be nice). Still, the intersection of two unrelated firsts scores high in statistical improbability, even if the shape can be explained, it still leaves open the question of why two never before seen events coincided with the first ever observed exo-asteroid.

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