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The interstellar object Oumuamua is almost certainly not an alien spaceship

NASA simulation of the object known as Oumuamua tumbling through space.
NASA simulation of the object known as Oumuamua tumbling through space. Credit: NASA

Ever since it was first spotted in 2017, the interstellar asteroid known as Oumuamua, meaning "scout" or "messenger" in Hawaiian, has garnered much interest among astronomers and the public. Its origins, composition and shape have grabbed peoples' imaginations. Now a forthcoming study from Harvard University researchers make the bold claim that the object is actually an alien spacecraft — or a "light sail" of alien origin — tumbling away from Earth.

The big picture: This study is not the first, nor is it likely the last time that an alien-origin hypothesis has been raised about Oumuamua. However, in science, the most outlandish claims are not usually the most likely, and they require rigorous examination by outside researchers before they can be accepted.

The details: This new study, first posted to Cornell University's arXiv e-print archive prior to its publication in Astrophysical Journal Letters, has the imprimatur of Avi Loeb, the chair of Harvard's astronomy department, which gives it some credibility.

  • The study focuses on an apparent acceleration in the object as it moved through our solar system, which scientists discovered in 2018 and attributed to dust and gases escaping the object as the sun warmed it up. Such outgassing is regularly observed in comets, but Oumuamua is not clearly defined as a comet.
  • However, the new study puts forward the possibility that the increase in speed could have come from solar radiation pressure. If this was the case, then it might mean that Oumuamua (pronounced oh-MOO-ah-MOO-a) is "a new class of thin interstellar material" that formed naturally or is alien in origin. Specifically, it could be a solar light sail, designed to be carried along by the solar wind.
  • Or perhaps it's something more fascinating, and possibly even frightening. The study states: "A more exotic scenario is that 'Oumuamua' may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization."

But, but, but: More information is needed before making any firm conclusions about Oumuamua. Loeb himself told NBC News, for example, that "It is impossible to guess the purpose behind Oumuamua without more data." Other researchers have cast further doubt on the alien origin hypothesis with observations from 2017 showing that there were no signals coming from it to indicate it was communicating in any way, per Mashable.

  • Although the paper is online already, it is pre-peer review and provides evidence of an anomaly that could allow for the possibility that Oumuamua is of alien origin, but does not prove that this is the case.
  • In addition, jumping to the conclusion that this is an alien spacecraft or a light sail, which is tempting from online news headlines, is akin to grabbing hold of the least likely explanation. After all, scientists are confident that alien life exists, but the most likely scenario for finding it is the discovery of microbial life on another planet, rather than an encounter with an alien spaceship traveling from another solar system.
  • In an interview with NBC, Coryn Bailer-Jones, an astronomer at the Max Planck Institute for Astronomy in Germany, summarized the reaction in the broader science community. "In science," he told the network, "we must ask ourselves, 'Where is the evidence?' not 'Where is the lack of evidence so that I can fit in any hypothesis that I like?'"
  • Via Twitter, Ohio State astrophysicist Paul Sutter bluntly refuted the study's claims. "No, 'Oumuamua is not an alien spaceship, and the authors of the paper insult honest scientific inquiry to even suggest it," he stated.

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Editor's note: This story has been updated to clarify the timing of Oumuamua's acceleration.

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