As far as I know, our current knowledge regarding the exact shape and size of ʻOumuamua is based on the analysis of its light curve and the assumption that it has a uniform albedo.

ʻOumuamua is very dark and too small to be resolved by even the largest telescopes as much more than a point of light. But so is Ultima Thule and we did manage to get a really good idea of its size and shape by observing stellar occultations caused by it.

Could the same technique be used to get a better idea of what shape ʻOumuamua really is? Or does its hyperbolic orbit render this kind of observation impractical? Have any attempts been made to perform such observations?


1 Answer 1


Observing star occultations is dependent on the object passing in front of a star.

During its short time in the inner solar system, ʻOumuamua didn't pass in front of a star (from the point of view of Earth) It is now beyond the orbit of Saturn. It became too dim for Hubble in about January 2018. There are no forecast occultations of any star (and its orbit is probably not well enough determined to predict any, given the observation of non-gravitational and not well-understood accelleration). Any occultation that did occur would only happen for a very short time and only be visible in a very narrow strip of the Earth. We can't set up large telescopes every 100m on Earth, and constantly observe all the (very dim) stars that might possibly dim further for half a second.

By contrast, Ultima Thule is a much larger object, with a well-known orbit, and the possibility of forecasting the exactly when and where an occultation of a reasonably bright star will occur, and set up observation stations on the narrow strip that is predicted.

So while an occultation could have told us about its shape, none occurred and none are expected.

  • $\begingroup$ What's confusing is that en.wikipedia.org/wiki/ʻOumuamua tells us that we know the color, size, and shape, even if it is an estimate. $\endgroup$
    – Max0815
    Commented Feb 22, 2019 at 2:59
  • 1
    $\begingroup$ How is that confusing? We know estimates the colour, size and shape from observations of the spectrum and light curve. Not from occultation $\endgroup$
    – James K
    Commented Feb 22, 2019 at 7:26
  • $\begingroup$ oh, I see. But how is that estimate gotten? $\endgroup$
    – Max0815
    Commented Feb 22, 2019 at 18:38
  • $\begingroup$ from observations of the spectrum and light curve. Check wikipedia/google. If you have a new question, feel free to ask in an new question thread. $\endgroup$
    – James K
    Commented Feb 22, 2019 at 18:43
  • $\begingroup$ no its ok. Its too much of a minute question easily understood. And I get it. $\endgroup$
    – Max0815
    Commented Feb 22, 2019 at 18:45

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