A little over a year ago, on October 17, 2017, scientists at the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii made a incredible discovery – they saw an object moving through our solar system at over 196,000 miles per hour. Incredibly, the trajectory of this object indicated that it originated outside of our solar system, which made it the first ever interseller object observed in our solar system. The scientists named it ‘Oumuamua, which means “messenger from far away” in Hawaiian.

That’s super cool, but it gets even cooler. ‘Oumuamua demonstrated nongravitational acceleration, which means it sped up more then would be expected based on normal gravitational pull as it moved through our solar system. That’s intriguing, but it could be explained by off-gassing if ‘Oumuamua was a comet. However, ‘Oumuamua doesn’t seem to be a comet – it has no obvious tail of debris behind it, and no coma, which is a hazy cloud of material around the leading edge of the comet.   ‘Oumuamua’s shape is unusual too – it’s long and thin, which is kinda… weird.

Now a new paper by the chair of the Harvard department of astronomy, Dr. Abrahman Loeb, suggests that maybe ‘Oumuamua was an alien spacecraft, or at least part of one. The author’s reasoning is based on solar wind. Solar wind is a stream of charged particles (mainly protons, electrons, and alpha particles) emitted by the upper atmosphere of the sun. Dr. Loeb hypothesizes that ‘Oumuamua may be solar sail, or at least part of a solar sail from a damaged craft. Acceleration from solar wind could explain the movement of ‘Oumuamua. A solar sail works much like a sail on a boat, except that the charged particles of the solar wind provides the kinetic engery to move the craft forward. In fact, such a concept has already been proven by three human-designed space craft: Japan’s IKAROS, NASA’s NanoSail D-2, and the non-profit Planetary Society’s LightSail. All of these crafts used solar sails to travel long distances across our solar system.

While ‘Oumuamua is long and thin, it would have to be really thin to work as a solar sale – less than 1 milimeter thick. Loeb and his postdoctoral co-author Shmual Bialy make the case that it would be possible for such a solar sail to survive the long journey from wherever it came from, and also that a coating of cosmic dust might make it less reflective than it really is.

Dr.’s Loeb & Bialy didn’t prove that ‘Oumuamua is an alien space craft – far from it. However, just the possibility is cool. We may never definitively know if ‘Oumuamua was of alien origin, especially since it is speeding out of our solar system as we speak. However, the prospect of being able to identify an alien spacecraft in the future means we should keep a close watch on the sky.