When the long, strange interstellar object ‘Oumuamua entered our solar system in 2017, rumors of its unknown origins began to fly. Is it a comet? A giant stone cigar? While it seems most likely that ‘Oumuamua is made of inert rock, Harvard scientists recently floated the idea that it could be an alien probe. This idea has unsurprisingly been met with its fair share of criticism, and now new evidence from the SETI Institute further supports the idea that ‘Oumuamua is not an alien probe.

In a preprint paper posted on arXiv in August, researchers led by SETI’s Gerry Harp, Ph.D., explained how they used the Allen Telescope Array to determine whether ‘Oumuamua was transmitting radio signals, which would suggest it was indeed an alien craft. But over a range of radio frequencies, the team found nothing. Harp is the director of the Center for SETI Research, and his team’s paper is available online ahead of print in the February 2019 issue of Acta Astronautica.

“We were looking for a signal that would prove that this object incorporates some technology — that it was of artificial origin,” Harp said on Tuesday. “We didn’t find any such emissions, despite a quite sensitive search. While our observations don’t conclusively rule out a non-natural origin for ‘Oumuamua, they constitute important data in accessing its likely makeup.”

‘Oumuamua Interstellar Visitor
‘Oumuamua is an interstellar visitor, so even if it wasn't sent by aliens, it's still fascinating.

Just because it (probably) wasn’t sent by aliens doesn’t mean ‘Oumuamua is any less unique. There’s a couple of factors that make ‘Oumuamua so fascinating to scientists, namely its origin and its odd movement.

An Interstellar Visitor

‘Oumuamua is the first interstellar object that scientists on Earth have observed. While comets and asteroids are interesting objects to observe in the night sky, most of them were either formed along with the rest of our solar system or were captured in the sun’s orbit so long ago that we never knew them when they were free agents. But, as shown in the video at the top of this article, ‘Oumuamua came from a distant solar system, zipping across our own solar system over the course of a year.

We first noticed it in October 2017 but it took until March 2018 for scientists to propose that it was ejected by a distant binary star system. Despite this partial explanation, the fact that ‘Oumuamua is most likely an asteroid is quite odd. These systems, astronomers say, are much more likely to kick out comets than asteroids, but ‘Oumuamua lacks a coma — the envelope of gas and dust usually surrounding a comet.

The Way It Moves

Even if it’s not transmitting any radio signals, ‘Oumuamua is still acting really weird. As it traveled through the solar system, the hunk of rock and metal sped up unexpectedly, which NASA scientists explained as an effect of outgassing, the process by which jets of material get expelled from its surface and provide many little boosts. At first, this sudden acceleration made ‘Oumuamua particularly intriguing, but like many astronomical objects that seem too strange to be true at first, there’s usually a pretty sensible explanation. We’re just not sure what it is yet.

Photos via NASA, ESA/Hubble; NASA; ESO; M. Kornmesser