Ever since the slender, cigar-shaped asteroid or comet or maybe alien spaceship named Oumuamua cruised through our solar system last year, scientists have wished it could have stayed a little longer and maybe posed for a few more close-ups. 

Now one of the most respected researchers studying the enigmatic visitor says there may be other interstellar objects like it already here, orbiting among the masses of space rocks that have been circling our sun for millions or even billions of years.

The oblong object dropped into our solar system sometime in 2017. It was spotted as it took a left turn around the sun and then flew back out to space, leaving earthlings to speculate almost nonstop about what it was and where it came from. Even weirder than its shape? It seemed to speed up on its way out of the solar system, further adding to the mystery.

Some kind of an asteroid, a dead or dying comet or even an alien craft from another solar system were among the early suggestions. As it was on its way out of the solar system, it was checked for radio signals that we'd expect to find emanating from a spaceship, but Oumuamua was dead quiet. It seemed to be just a rogue hunk of rock from very, very far away. 

That was until last month, when Harvard professor Avi Loeb and post-doctoral researcher Shmuel Bialy published a paper suggesting scientists should at least consider Oumuamua's strange acceleration could be explained another way. The "more exotic scenario is that Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization."

The study generated more worldwide attention than the original discovery of Oumuamua a year earlier, including plenty of raised eyebrows from other scientists. 

"The history of astronomy provides a cautionary tale about discoveries that were explained early on by positing extraterrestrial intelligence, but later explained by natural causes - from the detection of canals on Mars to the eerily regular cosmic beacons we now know as pulsars," Doug Vakoch, president of METI (Messaging Extraterrestrial Intelligence), told me. "We'll never know for sure whether Oumuamua is an alien technology, because we can't continue to observe it."

But a new paper from Loeb and Harvard undergraduate Amir Siraj looked at the orbits of known asteroids and says there could be at least four other observable objects in our solar system that came from across the galaxy like Oumuamua. But unlike the inscrutable interstellar traveler, they've stuck around.

"We find that four known objects have orbital parameters indicating their possible interstellar origin: 2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6," the new paper reads.

Even better: It should be possible to observe all four with the Large Synoptic Survey Telescope (LSST) that's now being built in Chile. 

"Once the Large Synoptic Survey Telescope comes online, we'll have a powerful instrument to search for additional interstellar visitors within our solar system," says Vakoch.

And what about the notion that Oumuamua could have been of "artificial origin"? 

To be clear, Loeb and his colleagues have never said the object definitely was the product of extraterrestrial intelligence, just that we should, you know, keep an open mind. In the latest paper naming the other four objects of potential interstellar origin, the authors conclude by winking at the notion once again:

"Exploration of trapped interstellar objects could potentially help reveal the prospects of life in other star systems as well as extraterrestrial artifacts. If no similar objects are detected by LSST, 'Oumuamua may have been a unique visitor (Loeb 2018)."

That last citation in parentheses refers to last month's paper that started the whole "is it aliens?" viral sensation. They're not saying it's aliens, but it could be unique indeed.

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