In October 2017, astronomers discovered the first known visitor from another star system as it hurtled away from the Sun. The interstellar object, named ‘Oumuamua, measured roughly a half-mile and sported an elongated shape that made it look like a cosmic blunt.
The object was so demonstrably weird that some scientists speculated it could have been an example of alien technology—perhaps even an attempt at first contact.
But a study published Monday in Nature Astronomy disputes this hypothesis and offers natural explanations for ‘Oumuamua’s admittedly bizarre and unexpected behavior.
Matthew Knight, an associate research scientist at the University of Maryland who co-led the study, told Motherboard that his team’s work doesn’t necessarily rule out an alien origin for ‘Oumuamua. However, it does suggest that a natural genesis for the object is more likely.
“As a scientist, I'm trained to not think in absolutes, so I can't say with 100% confidence that it *wasn't* aliens,” Knight noted in an email. “As we (as a community) have tried to explain some of the weird things about 'Oumuamua, it is certainly worth considering all hypotheses to see if we can solve the puzzle.”
“However, 'Oumuamua's having some unusual properties is by no means sufficient evidence to conclude that it must be aliens,” he emphasized.
Scientists have expected to detect an interstellar object for decades, but the conventional wisdom was that it would be an active comet, reminiscent of the frozen bodies that orbit the distant reaches of our solar system.
'Oumuamua, in contrast, was reddish in color and showed no detectable signs of outgassing, which is the release of gaseous emissions as comets warm up near stars. The lack of an observable cometary atmosphere further perplexed scientists once the object accelerated into the outer solar system—a process that is also normally associated with comets.
However, 'Oumuamua was relatively small and dim, so it’s possible that current observatories were simply not able to observe gas emissions from it. Alternatively, the object’s speed boost could be explained by the Sun’s radiation pressure on it, the team said.
As for its origins, the study concludes that 'Oumuamua was likely a planetesimal—a small building block of a planet—that was gravitationally catapulted out of its home system by a larger entity such as a gas giant.
Future detections of interstellar objects will hopefully shed more light on 'Oumuamua, which is why many astronomers are eagerly awaiting the completion of the Large Synoptic Survey Telescope (LSST) in Chile.
The telescope, which is on track to become operational in 2022, will be more sensitive to faint objects in the night sky. That will help it track down visitors from other star systems.
“Based on current theories about the numbers and sizes of interstellar objects, the [astronomical] community's expectation is that these improvements will allow us to discover interstellar objects more frequently,” Knight said.
The intense public fascination with extraterrestrial life is frequently a powerful way to connect people to scientific research, and 'Oumuamua is far from the first discovery that has sparked an alien-related frenzy.
But while enthusiasm for aliens can amplify important studies, it can also completely eclipse the original intent of the authors. “Invoking aliens undoubtedly gets more attention, but if it's not presented with appropriate caveats it is likely to be the only thing many people take away from a given story,” Knight said.
In other words, let’s celebrate 'Oumuamua for all the amazing things we do know about it, while we keep an eye out for future interstellar visitors that could tell us even more.
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