Investigation Into 'Oumuamua’s “Alien” Status Reveals a Natural Explanation

Scientists have been keeping a close watch on ‘Oumuamua, the cigar-shaped object from far beyond our own solar system that wandered toward us in 2017. Soon after, Harvard scientists proposed that it could be an alien probe sent from far away, stirring up even more interest in the mysterious object. A new article published Monday in Nature Astronomy, however, officially rules out the alien probe hypothesis — but that doesn’t mean we’ve learned all we can from ‘Oumuamua.

"We might have to rethink what is normal and instead think of our solar system as being weird!"

When scientists first took a close look at ‘Oumuamua in 2017, its strange shape raised eyebrows, as did its unexpected acceleration, which at first could not be explained by gravity alone. Those observations, among other strange characteristics, are what led the Harvard team to propose their alien hypothesis. But the new analysis, led by Matthew Knight, Ph.D., a research scientist at the University of Maryland’s astronomy department, leverages years of observations to argue that even ‘Oumuamua’s most suspicious qualities can be explained by the impressive natural forces that govern our universe.

Knight tells Inverse that our work on objects like ‘Oumuamua is just getting started. By 2022 he believes that new technology will help us answer a bigger question: Is ‘Oumuamua weird, or is it our solar system that’s unusual?

“We might have to rethink what is normal and instead think of our solar system as being weird!” says Knight.

How Do We Account for Oumuamua’s Weirdness?

Research published in March 2018 suggested that Oumuamua came from a binary star system with a hot, high-mass star. Knight and his team also propose that it was flung our way from its home system. They believe that it’s a planetesimal, which is a building block of a planet (or, at least, a piece of one). Knight favors the idea that it’s “a comet-like body that contained buried ice with a rather unusual composition.”

With its origin established, the paper then offers natural explanations for Oumuamua’s weirder aspects.

The strange upticks in speed can be explained by outgassing, as a 2018 study also noted. Outgassing is a release of gasses from an object, like a comet, as they are heated by the sun. That process likely propelled the Oumuamua along, resulting in a speed boost. 

Its strange, cigar-like shape can be explained in a few ways.

One idea is that ‘Oumuamua was reshaped passing close by a giant planet or a low-mass star that “tidally disrupted” its structure (essentially tore it apart using gravity). There are also two related theories proposing that it was either pelted by loads of tiny dust grains moving at high speeds or was squished between two other, large planetesimals.

Knight admits that he and his co-authors aren’t satisfied with any of these explanations so far, which is why they concede that ‘Oumuamua’s shape is still an open question. He is hopeful that we’ll have answers soon, though, because he thinks we will detect more objects like ‘Oumuamua.

A New Barometer for What Is “Weird”

Knight explains that ‘Oumuamua’s oddness raises a bigger question about what we consider odd. Is Oumuamua weird, or is our own solar system strange?

That, he says, depends on your reference point. We’re only beginning to have the capability to scan the skies for strange objects of all sizes. As our technology improves, we may start to notice many more objects like ‘Oumuamua before they come wandering into our view by accident.

“If we start seeing an appreciable number of interstellar objects and they frequently display properties that seem unusual compared to things in our solar system (such as their shapes being highly elongated or having seemingly exotic compositions), then we will be forced to reconsider how representative our solar system is compared to other solar systems,” says Knight.

The team is excited about a new telescope project called the Large Synoptic Survey Telescope, which is intended to begin operations around 2022. It’s slotted to take a 10-year survey of the sky and collect 15 terabytes of data every night. “LSST will be more powerful than any existing surveys,” says Knight, and thus will allow us to see fainter, more distant objects that come from faraway systems.

Those far-flung systems may be a lot different from our own, and there is some evidence that they too may have giant planets orbiting close to their stars. Because giant planets like our own Jupiter likely played a role in shaping the nature of comets and asteroids in our own solar system, these “hot Jupiters,” as Knight calls them, could be shaping objects in their own way that’s totally foreign to us since our solar system isn’t configured that way.

“It wouldn’t be terribly surprising to me if we started seeing evidence that our comets and asteroids are unusual,” he adds.

In the future, it may become clear that it’s not ‘Oumuamua that’s weird. It might just be us.

Abstract: The discovery of the first interstellar object passing through the Solar System, 1I/2017 U1 (‘Oumuamua), provoked intense and continuing interest from the scientific community and the general public. The faintness of ‘Oumuamua, together with the lim- ited time window within which observations were possible, constrained the information available on its dynamics and physical state. Here we review our knowledge and find that in all cases, the observations are consistent with a purely natural origin for ‘Oumuamua. We discuss how the observed characteristics of ‘Oumuamua are explained by our extensive knowledge of natural minor bodies in our Solar System and our current knowledge of the evolution of planetary systems. We highlight several areas requiring further investigation.