The Pan-STARRS1 Observatory in Hawaii first spotted the interstellar object now streaking through our solar system. 

Rob Ratkowski/University of Hawaii Institute for Astronomy

For the first time, astronomers are tracking a distant visitor streaking through our solar system

Around the world, telescopes are swiveling to welcome, and then wave farewell to, a new guest to the solar system: a fast-moving asteroid, or potentially a comet. It could be the first interstellar object to visit the solar system that has been detected and observed by astronomers, NASA announced yesterday.

Discovered on 19 October at the University of Hawaii’s Pan-STARRS 1 telescope on Haleakalā, the object, temporarily dubbed “A/2017 U1,” is 400 meters in diameter and moving quickly. It was first detected by Rob Weryk, an astronomer at the University of Hawaii (UH) in Honolulu, and confirmed by the European Space Agency’s telescope on Tenerife in the Canary Islands.

The object’s incoming motion—25.5 kilometers per second—was so extreme that astronomers believe it is not the kind of asteroid or comet typically seen inside the solar system. 

“This is the most extreme orbit I have ever seen,” said Davide Farnocchia, a trajectory expert at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, in a release. “It is going extremely fast and on such a trajectory that we can say with confidence that this object is on its way out of the solar system and not coming back.”

Based on its current trajectory, the visitor came from the constellation Lyra and approached our solar system from “above,” perpendicular to the plane that most planets orbit the sun. (NASA has prepared this nice visualization of the object’s path.) On 9 September, it made its closest approach to the sun, with gravity then tugging it on a route “under” the solar system. On 14 October, it made its closest pass by Earth, at 60 times the distance to the moon. It is now looping back above the planetary plane and, traveling at 44 kilometers per second, is shooting toward the constellation Pegasus.

A visualization of the path of that the asteroid or comet now named A/2017 U1 is taking through the solar system.


It’s no surprise that such a space rock, or comet, exists—scientists expect such grist to be wobbling around the galaxy, the ejected remnants of planetary formation. More observations are needed, and coming, to confirm its origins. Ultimately, the visitor will need a name, and rules do not yet exist for naming such extra–solar system guests.

“We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems. What’s most surprising is that we’ve never seen interstellar objects pass through before,” said Karen Meech, an astronomer at UH’s Institute for Astronomy in Honolulu specializing in small bodies and their connection to solar system formation.

Because this is the first object of its type ever discovered, rules for naming this type of object will need to be established by the International Astronomical Union.

“We have been waiting for this day for decades,” said JPL’s Center for Near-Earth Object Studies Manager Paul Chodas. “It’s long been theorized that such objects exist—asteroids or comets moving around between the stars and occasionally passing through our solar system—but this is the first such detection. So far, everything indicates this is likely an interstellar object, but more data would help to confirm it.”