In 2017, a mysterious interstellar object was viewed by astronomers 15 million miles away. By the time it was seen, the object was already hurtling out of our solar system at a staggering 110,000 mph.
Scientists gave the object a Hawaiian name - 'Oumuamua - translating roughly to "messenger from afar."
Harvard researchers famously speculated that there was a very small chance that the object was an alien spacecraft.
Now, scientists have released new research concluding that the flying object was almost certainly not alien.
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Why the alien speculation?
Due to 'Oumuamua's trajectory, it was named the first-ever interstellar object ever to be witnessed in our solar system.
This, as well as the object's odd characteristics, led Harvard scientists to speculate that there was a chance the object was not merely a rock hurtling through space.
In an Astrophysical Journal Letters paper detailing the original findings, researchers proposed an "exotic scenario:" "‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization."
'Oumuamua was initially classified as a comet, though it doesn't emit gases as comets typically do. Its trajectory and spin speed are also not easily explained by gravity, suggesting it's not an asteroid.
Furthermore, the object's odd cigar shape — it is only 114 feet wide despite being a quarter of a mile long — doesn't match any previously observed asteroids or comets.
Despite the fact that it is the size of a skyscraper, 'Oumuamua is now too dim to be viewable by telescopes on Earth.
Unfortunately, the mysterious space object's increasing distance from our solar system, at the time of the first sighting, meant that scientists had a short window in which to take readings. This lack of concrete findings only helped to fuel speculation.
A new study, published this week in journal Nature Astronomy, analyzed the existing data about 'Oumuamua and came to the conclusion that the alien theory is incredibly unlikely.
"The alien spacecraft hypothesis is a fun idea, but our analysis suggests there is a whole host of natural phenomena that could explain it," Matthew Knight, an astronomer who co-led the study, said in a press release.
"This thing is weird and admittedly hard to explain, but that doesn't exclude other natural phenomena that could explain it," he added.
For example, 'Oumuamua could have been ejected by a gas giant planet orbiting another star. Theories suggest that Jupiter created the Oort cloud in the Milky Way, a huge shell of small objects at the outer edge of our solar system, that is also thought to have propelled interstellar objects into distant space.
Knight and his team also feel that thanks to improving data from technology such as the Large Synoptic Survey Telescope (LSST), we will soon know more about how unusual 'Oumuamua really is.
"We may start seeing a new object every year. That's when we'll start to know whether 'Oumuamua is weird, or common," Knight said. "If we find 10 to 20 of these things and 'Oumuamua still looks unusual, we'll have to reexamine our explanations."
The research was carried out by a team at the University of Maryland Department of Astronomy.