Interstellar Rock `Oumuamua Might be Alien Light-Sail Spacecraft

Alien spy?
The mysterious interstellar object named Oumuamua (artist's concept) (Photo: NASA)

An odd, cigar-shaped "thing" that's since been called an "interstellar object" after its discovery a year ago might -- might -- be an alien spacecraft probing our planet.

This thing has been named "'Oumuamua," which is a Hawaiian word meaning "a messenger that reaches out from the distant past." Formally designated 1I/2017 U1, 'Oumuamua was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory in Hawaii, on Oct. 19, 2017, or 40 days after it passed its closest point to the Sun.

Since its discovery, 'Oumuamua has exhibited actions inconsistent with a hunk of rock hurtling mindlessly through space. Because of this, scientists have been at odds to explain Oumuamua's actions, unusual features, and precise origins.

Scientists first called this thing that's been tumbling through space a comet and then an asteroid. Unable to agree, they made 'Oumuamua the first member of a new class of thing. They called it an "interstellar object."

'Oumuamua is an elongated, dark red object that shows no signs of a cometary tail or coma despite its close approach to the Sun. It's 10 times as long as it is wide and is tumbling along at speeds of 315,000 km/h.

Oddly, the object has since undergone non-gravitational acceleration, which some scientists say is consistent with a push from solar radiation pressure, or was caused by outgassing. Two scientists beg to differ, however.

Shmuel Bialy and Prof. Abraham Loeb at the Harvard Smithsonian Center for Astrophysics claim 'Oumuamua might have an "artificial origin." In a recently published study -- Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration? - Bialy and Loeb suggest 'Oumuamua "may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.".

They based their conclusion on 'Oumuamua's "excess acceleration," or its unexpected boost in speed as it traveled through and out of our Solar System in January 2018. More specifically, they believe 'Oumuamua is, in reality, a "light-sail spacecraft."

Considering 'Oumuamua to be of artificial origin, one possibility is this mystery object is a light-sail floating in interstellar space as a debris from an advanced technological equipment.

Bialy and Loeb dismissed the outgassing explanation as causing 'Oumuamua's inexplicable acceleration. They said if 'Oumuamua were, in fact, a comet, why then did it not experience outgassing when it was closest to our Sun?

They also cited other research showing that if outgassing were responsible for the acceleration, it would have also caused a rapid evolution in 'Oumuamua's spin, which wasn't observed.

Bialy and Loeb entertain the possibility 'Oumuamua might, in fact, be a light-sail. A light sail is a type of spacecraft that relies on radiation pressure to generate propulsion.

Both scientists brush-off the argument the excess acceleration of 'Oumuamua away from the Sun is the result of the force that the sunlight exerts on its surface. For this force to explain measured excess acceleration, the object needs to be extremely thin, of the order a fraction of a millimeter in thickness but tens of meters in size.

This makes 'Oumuamua lightweight for its surface area and allows it to act as a light-sail. It might either be natural in origin or artificial (as a probe on a reconnaissance mission to the Solar System).

Based on this, Bialy and Loeb calculated the likely shape, thickness, and mass-to-area ratio that such a spacecraft would have.  They discovered that a sail only a fraction of a millimeter thick (0.3-0.9 mm) is sufficient for a sheet of solid material to survive the journey through the Milky Way.

This light-sail is able to withstand collisions with dust-grains and gas ever-present the interstellar medium. It can also survive centrifugal and tidal forces.

The scientists suggest the probe might actually be a defunct sail floating under the influence of gravity and stellar radiation. This would make this object similar to debris from ship wrecks floating in the ocean. This helps explain why Breakthrough Listen found no evidence of radio transmissions.

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