ESO image
image from

Today I came across something on the web that’s actually interesting. It’s on the website that I usually visit daily – I’ve linked to today’s archive so it can be found again. It’s about ‘Oumuamua.

The pretty pictures are of course artwork, and I’ve linked the one above to the BBC article it came from, as part of the story about this object. The latest paper suggests that the properties of this object are compatible with it being a piece of alien hardware – which is utterly fascinating!

It was discovered by the PAN-STARRS1 survey (on 19 October 2017), and represents the first interstellar object, on an orbit coming from outside the solar system (and returning into interstellar space), that has been discovered. Here are the key points:

  1. Its orbit is such that its velocity is too great for it to be captured by the Sun – it really is extrasolar.
  2. From the way its light appears and fluctuates regularly, it was deduced that the object is a rotating, cigar shaped asteroid, similar to those in our own solar system, but originating near another star.
  3. It could have been an icy comet, but it displayed none of the behaviour associated with comets; it didn’t develop a halo or tail (due to heating by the Sun), even though at its closest approach to the Sun it was only a quarter of the distance of the Earth from the Sun.
  4. The observation of ‘Oumuamua also suggests that there are far more interstellar asteroids than any of our models of stellar system formation would suggest, which is problematic.
  5. As it left the sun, a non-gravitational (i.e. not caused by other objects) acceleration away from the Sun was observed. One study concluded that this could be due to cometary activity – outgassing of material due to solar heating, acting like a rocket thruster.
  6. The latest paper released on 1 November points out that (1) no cometary activity was observed close to the Sun, which would have been expected, and (2) such outgassing would have caused a rapid change in spin, which is incompatible with observations.
  7. The authors (Bialy and Loeb) suggest that the observations are compatible with the object being a thin sheet, accelerated by the radiation pressure from sunlight. The observed acceleration also matches what would be expected with such an object.
  8. Various people have suggested that this mechanism should actually be used to help move spacecraft around the solar system; the device is called a “lightsail” and though extremely thin and large would be easy to deploy in space.
  9. Bialy and Loeb conclude that the object could be an alien lightsail from a distant stellar system, possibly debris after it had been used for transportation within the system.
  10. They even suggest that it could be some form of operational probe, which would explain why it came so close to the Sun. Unfortunately it is now far too late to send a probe to view it; even had we tried this when it was first discovered, it would have been difficult and costly.


Here’s another longer description from