Is Oumuamua an asteroid? An explanation weirder than aliens

The space object named Oumuamua (Hawaiian for "scout" or "messenger") got lots of overheated attention this week after a widely respected Harvard scientist co-authored a paper suggesting the interstellar visitor could have been an alien spacecraft powered by solar radiation pressure.

In fact, the new paper by Abraham Loeb and post-doctoral researcher Shmuel Bialy, which is still working its way through the peer review and publication process, seems to have garnered more attention than the original 2017 discovery of the first thing to pass through our solar system from beyond.

Earlier, research teams suggested Oumuamua might be an alien probe and then used radio telescopes to scan it for any signs of artificial signals. Those observations all came back negative. We'll probably never be able to investigate Loeb and Bialy's hypothesis fully, however, as Oumuamua has been traveling away from Earth at very high speeds for over a year now.

Astrophysicist and cosmologist Katie Mack (no relation) suspects the fact that it's difficult to disprove the "it might be aliens" theory might be part of the calculation behind publishing the paper.

"If you come up with something in the category of "not *obviously* wrong and also HUGE IF TRUE," the chance that publishing it will backfire is small, and the low-probability high-reward payoff might be tempting enough to make it worth facing the eyerolls of your colleagues," Mack tweeted about the paper and the huge response it's received.

So if you come up with something in the category of “not *obviously* wrong and also HUGE IF TRUE,” the chance that publishing it will backfire is small, and the low-probability high-reward payoff might be tempting enough to make it worth facing the eye-rolls of your colleagues.
— Katie Mack (@AstroKatie) November 6, 2018

In other words, anytime something mysterious happens that's difficult or impossible to perform follow-up studies on, you just can't completely rule out aliens as a plausible explanation. Furthermore, anytime aliens could be a plausible explanation for something, someone is sure to step in and fill that vacuum. This time around a big-deal Harvard astrophysicist and cosmologist filled that void, which caused the internet to convulse.

There's no actual hard evidence Oumuamua is an alien spacecraft -- Loeb just happened to notice that it moved in a manner similar to how we might expect a so-called "light sail" craft like the one the Breakthrough Starshot initiative is working on to fly. (Loeb also happens to chair Breakthrough Starshot's advisory committee.)

Loeb and Bialy's paper is just one of literally dozens about Oumuamua out there. It's not the first to propose the object could be artificial and it's not even the weirdest proposed origin story for the big interstellar cylinder or cigar or whatever you think it looks like. Here's a brief rundown of the other theories for where Oumuamua came from.

The invisible universe made visible?

One of the earlier and more far-out explanations proposed Oumuamua could actually be a big hunk of "macroscopic dark matter." Dark matter is the unseen material thought to make up much of the universe.

"Contrary to widely held misconceptions, dark matter need not be in the form of weakly interacting elementary particles, but might instead be found in much larger pieces," reads the very brief paper by scientists at Case Western Reserve University, Canada's Perimeter Institute and Stanford.

The researchers posit that if their hypothesis were true, Oumuamua's passage could have altered the orbits of Mercury, Earth and the moon. No one has yet confirmed any changes to those planetary paths.

Crumbs from another solar system

One of the most popular explanations for Oumuamua's origin in the literature is the idea that it's left over from the process of planetary formation around another distant star. Basically just an interstellar asteroid from across the cosmos.

It's thought the early days of any solar system can be particularly turbulent and chaotic with pieces of debris all over the place and some might even get knocked out of the system altogether.

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One recent study used new data to try to narrow down exactly which star systems the vagabond object may have been exiled from.

Another theory suggests Oumuamua may come not from the scraps of planetary formation, but from the leftovers of a planet's destruction.

"I conclude that the origin of Oumuamua as a fragment from a planet that was tidally disrupted and then ejected by a dense member of a binary system could explain its peculiarities," the SETI Institute's Matija Cuk writes in an article in the Astrophysical Journal Letters.

The idea here is that a run-in with a dense red dwarf star may have ripped a planet apart, flinging at least one cigar-shaped piece in our direction.

A comet out of a coma

Another early explanation was that Oumuamua was some sort of weird comet from another side of the galaxy shaped like no comet we've ever seen and lacking an obvious tail. It did, however accelerate on its way out of the solar system like a comet might as it gets a boost from heated ice and water aboard on its pass by the sun.

Various researchers have suggested perhaps it was a dead comet nucleus, a comet that was fragmented in a manner similar to the aforementioned planet fragment explanation or just a comet-like uh... thing.

Not that alien after all

There have also been a few suggestions that Oumuamua might not have even been that alien. Some of the most recent research explores whether it may have actually come from the edges of our own solar system. One paper went so far as to suggest its odd behavior and trajectory might be explained by having been "scattered" by a "yet unknown" planet in our solar system.

Yes, that's a reference to what's sometimes called Planet 9 or Planet X, another oft-confused and conflated concept that tends to drive the internet wild.

A follow-up paper by noted astronomer Jason Wright from Penn State throws cold water on the idea that an unseen planet might have flung Oumuamua at us, however.

As long as it stays on its current path, the mystery of humanity's first interstellar fly-by will remain. Well, unless 'Oumuamua suddenly makes a U-turn.

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