Interstellar object is cookie-shaped shard from planet
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 is shaped like a cookie.
Arizona State University astronomers reported last week that the 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 the sun.
It’s named Oumuamua (Hawaiian for scout) in honor of the Hawaii observatory that found 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.
Using its shininess, size and shape — and that it was propelled by escaping substances that didn’t produce a visible tail — Mr. Jackson and Mr. Desch devised computer models that helped them determine Oumuamua was most likely a chunk of nitrogen ice being gradually eroded, the way a bar of soap thins with use.
Their two papers were published Tuesday by the American Geophysical Union and also presented at the Lunar and Planetary Sciences Conference.
Not all scientists buy it. Harvard University’s Avi Loeb stands by his premise that the object appears to be more artificial than natural — in other words, something from an alien civilization. His newly published book “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth,” addresses the subject.
Given that Oumuamua is unlike comets and asteroids, “we cannot assume ‘business as usual,’ as many scientists argue,” Mr. Loeb wrote in an email.
When Oumuamua was at its closest approach to Earth, it appeared to have a width six times larger than its thickness. Those are the rough proportions of one wafer of an Oreo cookie, Mr. Desch noted.
It’s 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. As a result, astronomers will need to rely on the original observations and continue to refine their analyses, Mr. Jackson said.