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 object to pass through our solar system from beyond.
But the truth is no-one knows exactly what Oumuamua is and the idea that it might be of alien origin isn't even necessarily the strangest theory put forward.
Earlier, research teams suggested Oumuamua might be a probe and used radio telescopes to scan it for signs of artificial signals. Those observations all came back negative. Sadly we'll probably never be able to investigate Loeb and Bialy's hypothesis fully 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 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 eye-rolls of your colleagues," Mack tweeted about the paper and the huge response it's received.
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 a big-deal Harvard astrophysicist and cosmologist filled that void, which caused the internet to convulse.
Best places in space to search for alien life
The deeper we look into space, the more places we come across that seem like maybe, just maybe, could host life. From our neighboring planets to distant galaxies sending out weird signals, the list of spots in space worth checking out just continues to grow.
The closest world we should check for signs of life is one we've already been to, or at least our robots have. There's increasing evidence that Mars was once a lot more like Earth, with oceans on its surface. Today it's more harsh, but it's not out of the question that we could find some sort of microbes in Martian soil.
Dwarf planet Ceres in the asteroid belt is full of surprises. It started with those big bright spots that turned out to be salt deposits, and there's also a huge, strange pyramid-shaped mountain, plenty of water beneath the surface and even the building blocks of life. Some people already believe this huge rock is actually an alien ship. The evidence isn't there to support that theory, but the place does seem worth a closer look.
We don't think of the largest gas giant planet around as a place to look for life, but science fiction author Ben Bova has other ideas.
"It's got all the ingredients, enough room and lots of energy," he said in 2016.
Bova briefly explained his notion of life-forms that might be able to live in the air or in water underneath Jupiter's dense deck of clouds. He referred me to a few of the novels from his "Grand Tour" series, including "Jupiter" and "Leviathans of Jupiter."
The storyline of the novels revolves around the existence of massive, city-size life-forms called Leviathans living in gigantic oceans that have condensed beneath the clouds of Jupiter.
Um, sure. Why not?
Saturn's satellite Titan is the rare moon in our solar system with an atmosphere, weather, seas and rivers. It sure looks like home, except it's freezing and the lakes are flammable. Whatever life could survive there would be awfully weird, but scientists would still love to send a submarine to see for themselves.
Like Europa, Saturnian moon Enceladus has an icy shell with plumes shooting into space. In 2015, the Cassini spacecraft actually flew through one of the plumes and found large amounts of hydrogen present in its hidden ocean. This suggests the watery world has just about all the ingredients required to support life.
Jupiter moon Europa not only hides a subsurface ocean beneath its icy shell, but geysers have also been spotted there, hinting that some sort of hydrothermal activity might be able to support marine life.
Jupiter's moon Callisto is another world that harbors an unseen ocean. Checking it for microbes or any other exotic life forms might be tough, though, because it would require drilling through its huge, rocky exterior.
Ganymede, Jupiter's largest moon, has long been suspected of harboring a subsurface ocean. In 2015, scientists said they could confirm a salty ocean beneath its frozen crust. It also has a thin oxygen atmosphere, adding to its intrigue.
Yes our nearest planetary neighbor is supposed to be a horrible, hot and toxic hellscape, but that's just below the clouds. Higher in the atmosphere it could be quite nice. The planet wasn't always so inhospitable, so perhaps something managed to adapt? Scary to imagine what might have managed that, but you know you want to see it.
This former planet is very cold, but it's also more interesting than we used to think, with hints of active geology, lots of ice and perhaps some hidden oceans of its own. Definitely worth adding to the life-prospecting itinerary.
A potentially habitable planet around the nearest star to the sun, Proxima b is a no-brainer for closer examination. In fact, some told stories about alien civilizations there before the planet was even discovered. Plans are already underway to send tiny craft there to see if anyone is about.
The TRAPPIST-1 system is just 40 light-years away and hosts up to seven Earth-sized planets, all very close to each other and perfect for the space-faring civilization of our sci-fi dreams.
Wolf 1061 c is a "super-Earth" just 14 light-years away, making it one of the top five closest potentially habitable planets orbiting another star. We've known about it for a few years, and scientists have already started checking it for alien transmissions.
Mysterious signals known as "fast radio bursts" have baffled astronomers for a decade. The only such signal that repeats has been traced to a tiny galaxy in this image in the constellation Auriga. Is it E.T. phoning home?
Something weird is going on around the distant star KIC 8462852, also known as Boyajian's Star. After a few years of research, no one knows for sure what's happening, but one explanation that's yet to be completely ruled out is the far-out notion that a highly advanced society is building insanely huge megastructures in space that obstruct the star. Gulp.
There's no hard evidence Oumuamua is an alien spacecraft -- Loeb just happened to notice it moved in a manner similar to a so-called "light sail" craft, like the one the Breakthrough Starshot initiative is working on. (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 an interstellar asteroid from across the cosmos.
It's thought the early days of any solar system is turbulent and chaotic. With pieces of debris all over the place some might even get knocked out of the system altogether.
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: 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 even be that alien. Some of the most recent research explores the idea it may have 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.