The origin and identity of a massive space object that passed Earth in 2017 has been a mystery ever since.
The object, called ‘Oumuamua – a Hawaiian name meaning “scout” or “messenger” – traveled on a trajectory that strongly suggested it came from another star system. That made it the first interstellar object ever detected.
But what was it? Some researchers, including Harvard University astronomer Avi Loeb, postulated that the object was an alien spacecraft. Others suggested it was an asteroid, or perhaps an interstellar comet.
Now a couple of articles published in an American Geophysical Union magazine offer another theory: that ‘Oumuamua was shrapnel from a small planet in a different solar system.
“We’ve probably solved the mystery of what ‘Oumuamua is, and we can reasonably identify it as a chunk of an’ exo-Pluto, ‘a Pluto-like planet in another solar system,” said Steven Desch, an Arizona state astrophysicist. University and a co-author of the new study, said in a press release.
A planetary fragment made of frozen nitrogen.
Desch and his co-authors think that 500 million years ago, a space object struck ‘Oumuamua’s parent planet. That sent ‘Oumuamua hurtling towards our solar system.
Once he got closer to the sun, his thoughts say, ‘Oumuamua sped up as the sunlight vaporized his icy body. Comets follow a similar pattern of motion, known as the “rocket effect.”
Because the composition of ‘Oumuamua is unknown, the researchers calculated which types of ice would sublimate (change from solid to gas) at a rate that could explain’ Oumuamua’s rocket effect. They concluded that the object is likely made of nitrogen ice, like Pluto’s surface and Pluto’s moon Triton.
An enhanced color view of Pluto, taken by NASA’s New Horizons spacecraft.
NASA / JHUAPL / SwRI
As it approached our solar system, and therefore the sun, ‘Oumuamua began to shed layers of frozen nitrogen. The object entered our solar system in 1995, although we didn’t realize it at the time, then it lost 95% of its mass and melted into a splinter, according to the study authors.
It is a comet. It is an asteroid. No, it is none.
An illustration of the ‘Oumuamua space object flying through the solar system in late 2017.
NASA / ESA / STScI
When astronomers became aware of the existence of ‘Oumuamua in 2017, it was already moving away from Earth at 196,000 mph. So they only had a few weeks to study the strange skyscraper-sized object. Several telescopes on the ground and one in space took limited observations as the object flew, but astronomers were unable to examine it in its entirety. ‘Oumuamua is now too far away and too dark to continue observing with existing technologies.
The limited nature of the information collected left room for scientists to offer guesses as to what the object might be and where it came from. ‘Oumuamua was initially classified as a comet, but it did not appear to be made of ice and did not emit gases like a comet would.
Oumuamua’s spin, speed, and trajectory couldn’t be explained by gravity alone, suggesting that it wasn’t an asteroid either. And the shape and profile of the object (it is about a quarter mile long but only 114 feet wide) does not match that of any comet or asteroid observed before.
However, according to the authors of the new study, the frozen nitrogen composition of ‘Oumuamua could explain that shape.
“As the outer layers of nitrogen ice evaporated, the body shape would have become progressively flatter, just like a bar of soap does when the outer layers rub off with use,” said Alan Jackson, another study co-author. in the statement.
Some astronomers still think it was an alien ship.
Unlike most space rocks, ‘Oumuamua appeared to be accelerating, rather than decelerating, in the telescope observations.
That’s partly why Loeb thinks’ Oumuamua was an alien spaceship. In a book he published in January, titled “Alien: The First Sign of Intelligent Life Beyond Earth,” Loeb describes’ Oumuamua as a missing piece of alien technology.
“The object has anomalies that deserve some attention, things that don’t line up the way we expected,” he told Insider in December. “Other people say, ‘Let’s put these anomalies under the rug of conservatism.’ I have a problem with that because when something doesn’t fit, you have to say so. “
An artist’s rendering of ‘Oumuamua.
ESA / Hubble; POT; THAT; M. Kornmesser
Still, a 2019 study by an international group of astronomers analyzed all available ‘Oumuamua data and concluded that Loeb’s theory was unlikely.
“We found no convincing evidence favoring an extraterrestrial explanation for ‘Oumuamua,” the astronomers wrote.
Matthew Knight, an astronomer at the University of Maryland who co-wrote the study, put it this way: “This is strange and certainly difficult to explain, but that does not exclude other natural phenomena that could explain it.”