WASHINGTON (Reuters) – Oumuamua spotted in 2017 speeding through our solar system, astronomers remain uncertain about how to classify it, but are confident it is not an alien spaceship.
This artist's impression shows the first-known interstellar object to visit the solar system, 'Oumuamua, which was discovered on October 19, 2017, by the Pan-STARRS 1 telescope in Hawaii, US, with subsequent observations from ESO's Very Large Telescope in Chile and other observatories around the world. European Southern Obervatory / M. Kornmesser / Handout via REUTERS
Oumuamua – the first object from another star system. But after poring over the data, an international team of researchers wrote that "we're no compelling evidence to favor an explanation."
Scientists tracked the reddish-colored 'Oumuamua from Oct. 14, 2017, until Jan. 2, 2018, after which it became too faint to detect even the most powerful telescopes. It is estimated to be a half-mile (800 meters) long, tumbling through space.
"Oumuamua's properties are consistent with a natural origin, and an explanation is unwarranted," said University of Maryland astronomer Matthew Knight, co-leader of the published research in the Nature Astronomy.
"Yes, if it were a sudden, unexplainable turn that would have warranted further exploration," Knight added.
'Oumuamua (pronounced oh-moo-uh-moo-uh) was first detected by the University of Hawaii's Pan-STARRS1 telescope. Its name in the native Hawaiian language means a messenger arriving from a great distance.
Knight said it is not easy to fit 'Oumuamua into familiar classifications' as a comet or asteroid.
"We have tried to put it in one of those boxes and prefer to call it more generically on 'object,'" Knight said.
"In simple terms, asteroids are rocky and devoid of ices, while comets are a mixture of rock and ice, so-called 'dirty snowballs,'" Knight added.
'Oumuamua was somehow ejected from a distant star system, traversing through interstellar space and through our solar system small emission of gas from its surface, indicative of a comet, though any such emission is so slight as to be undetected. It painted a dust tail or gas jet, characteristic of comets.
The researchers wrote that a "straightforward explanation for Oumuamua is a planetary" – a planetary building block – or a fragment of one – formed in a faraway star system.
Its composition remains a mystery, including whether it is just rock or includes some metal or other ingredients. It is currently located beyond Saturn, dashing out of our solar system.
Reporting by Will Dunham; Editing by Sandra Maler