• In October 2017, astronomers observed an object moving so quickly, it could only have come from another star — the first recorded interstellar interloper.
  • It didn’t seem to be an ordinary rock, because after slingshotting around the Sun, it sped up and deviated from the expected trajectory, propelled by a mysterious force.
  • This could be easily explained if it was a comet expelling gas and debris — but there was no visible evidence of this “outgassing.”
  • The traveler also tumbled in a strange way — as inferred by how it got brighter and dimmer in scientists’ telescopes, and it was unusually luminous, possibly suggesting it was made from a bright metal.