CAPE CANAVERAL, Fla. – Our solar system’s first known interstellar visitor is neither a comet nor asteroid as first suspected and looks nothing like a cigar. A new study says the mystery object is likely a remnant of a Pluto-like world and shaped like a cookie.
Arizona State University astronomers reported this week that the strange 148-foot object appears to be made of frozen nitrogen, just like the surface of Pluto and Neptune’s largest moon, Triton.
The study’s authors, Alan Jackson and Steven Desch, think an impact knocked a chunk off an icy nitrogen-covered planet 500 million years ago and sent the piece tumbling out of its own star system, toward ours. The reddish remnant is believed to be a sliver of its original self, its outer layers evaporated by cosmic radiation and, more recently, the sun.
It’s named Oumuamua, Hawaiian for “scout,” in honor of the observatory in Hawaii that discovered it in 2017.
Visible only as a pinpoint of light millions of miles away at its closest approach, it was determined to have originated beyond our solar system because its speed and path suggested it wasn’t orbiting the sun or anything else.
The only other object confirmed to have strayed from another star system into our own is the comet 21/Borisov, discovered in 2019.
But what is Oumuamua? It didn’t fit into known categories – it looked like an asteroid but sped along like a comet. Unlike a comet, though, it didn’t have a visible tail. Speculation flipped back and forth between comet and asteroid – and it was even suggested it could be an alien artifact.
“Everybody is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens,” Desch said.
Using its shininess, size and shape – and the fact that it was propelled by escaping substances that didn’t produce a visible tail – Jackson and Desch devised computer models that helped them determine Oumuamua was most likely a chunk of nitrogen ice being gradually eroded.
Their two papers were published Tuesday by the American Geophysical Union and presented during the Lunar and Planetary Sciences Conference, typically held in Houston but virtual this year.
The object is now long gone, beyond the orbit of Uranus, more than 2 billion miles away – and far too small to be seen, even by the Hubble Space Telescope.