When the first object known to visit Earth’s solar system from space flew in 2017, it was so strange that at least one leading astronomer was convinced it was an alien craft. But researchers on Wednesday said they’ve found a simple, “non-alien convincing explanation” for the interstellar interference’s strange behavior, although not everyone is convinced.

The object, named Oumuamua, meaning “exploration” in Hawaiian, surprised scientists as soon as it was spotted by an observatory in Hawaii six years ago.

Astronomers have long searched for comet-like objects that enter the solar system from the depths of interstellar space, but have never observed them before. But Oumuamua didn’t look much like comets, which usually come from the fringes of the solar system. It had neither a tail nor a pale halo of solar-heated dust and gas known as a coma.

It was also a strange, elongated shape never seen before in comets or asteroids. It was about 100 meters in diameter – about the size of a football field – but by some estimates it was 10 times its width and was shaped like a pancake or a cigar. And judging by the way the light was reflected off the object, the object seemed to be approaching.

But the strangest of all was that when ‘Oumuamua was launched around the Sun, it was accelerated and deflected from its expected orbit, pushed by a mysterious force in its path from the solar system. Scientists are left with four months of seemingly contradictory data to try to make sense of, which has led to a host of theories.

“Engine Acceleration”

Jennifer Bergner, an astrochemist at the University of California at Berkeley and co-author of the new study, told AFP that many of the theories “blow the imagination.” His hypothesis is that where Oumuamua came from, it was actually a water-rich comet object.

During interstellar travel, it was blasted off by penetrating cosmic rays that converted some of its water into hydrogen trapped in the object’s body. As it approached the Sun, Oumuamua said, the heat acts as a “pusher” that puts the object on its unexpected path, releasing the trapped hydrogen. “Jenny is absolutely right about the trapped hydrogen,” said Darryl Seligman of Cornell University, one of the authors of the study published in the journal Nature.

“We’ve had all these crazy ideas like hydrogen icebergs and other crazy things, and that’s just the most general explanation,” he said in a statement.

Marco Micheli, an astronomer at the European Space Agency who was not involved in the work, commented in Nature that the paper “offers perhaps the first simple and physically realistic explanation for the properties of this object.”

“Very suspicious”

Not everyone was convinced.

Avi Loeb, a renowned theoretical physicist and longest-serving chair of astronomy at Harvard University, particularly in his 2021 book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, argues that the simplest explanation is “Oumuamua is alien technology.”

Loeb dismissed the new theory, telling AFP that claiming a comet without a tail “is like saying an elephant is a zebra without stripes.”

It pointed to the large comet tail seen at 2I/Borisov, the second known extrasolar visitor detected in 2019. Roman Rafikov, of the University of Cambridge in England, said he had previously shown that if there were trapped gas behind Oumuamua’s acceleration, it would “drastically” change its rotational speed, but not change it. Rafikov said he was “very skeptical” of such theories, adding that he preferred “an explanation that does not involve aliens or divine powers.”

Bergner suggested that the reason Oumuamua didn’t have a tail or coma was because it was much smaller than any comet ever observed, including Comet 2I/Borisov. But that may soon change.

In the coming years, potentially many more comets, both from within the Solar System and beyond, could be detected by the Rubin Legacy Space and Time Observatory in Chile, whose imaging project is expected to begin in 2025. If small comets show signs of captive hydrogen release and don’t have tails or clusters, this could help support his theory, Bergner said. As for ideas about extraterrestrial life, he said, “it depends on what standard of evidence you need to talk about aliens.”

“We’ll never be sure what ‘Oumuamua is – we’re out of luck,” he said. “But for now, I think we have a credible explanation for the non-alien.”