Sometimes, a journey of a thousand light-years ends in flames. A few minutes after 3 a.m. on January 9, 2014, a fireball burned through the skies just off the northeast coast of Papua New Guinea; it was a meteor disintegrating in Earth’s atmosphere, as so many meteors do.
But according to new research, this early morning visitor wasn’t just any old space rock going out with a bang. It was an interstellar interloper, a visitor launched into the cosmos from deep within another star system.
If confirmed, the meteor will be only the second such object ever spotted by humans. The first, a bizarrely shaped space rock now called ’Oumuamua, whizzed through our solar system in 2017 and is now on its way back to the stars. By contrast, the 2014 meteor ended its travels here, making it possibly the first known rock from beyond the solar system to crash into Earth's atmosphere.
“I was very surprised. I didn’t expect that. I thought we will not see anything,” says Avi Loeb of the Harvard-Smithsonian Center for Astrophysics, who describes the finding in a paper submitted to the Astrophysical Journal Letters. “But in retrospect, like any discovery, you say, Oh yeah, of course. How could I be so foolish not to look for that in the first place?”
Loeb and Amir Siraj, a Harvard undergraduate, spotted the marauding meteor in a catalog compiled by the Center for Near Earth Object Studies. Kept by NASA’s Jet Propulsion Laboratory, the catalog contains a record of the times, dates, locations, and velocities of incoming meteors.
Earlier this year, while scanning the catalog’s records of meteoritic fireballs known as bolides, Siraj spotted one with an unusually high velocity. Traveling at nearly 37 miles a second relative to the motions of the sun and Earth, it was moving much too quickly to be gravitationally bound to our home star. Suspecting they might have spotted another interstellar object, Siraj and Loeb used the catalog’s information to derive an orbit for the oddball meteor.
“We know the motion of the Earth [and] we correct for it—for the gravity of Earth, gravity of the sun, gravity of all the planets,” Loeb says. Using that information, the cosmic detectives could then trace the meteor’s probable path.
Eventually, they calculated that the South Pacific meteor had not grabbed a speed assist by slingshotting around other planets in our solar system, a trick NASA often uses to send spacecraft farther from Earth. They also found that the meteor was on an unbound hyperbolic orbit, which means it definitely did not originate from within our solar system. Instead, the team suspects that it comes from the deep interior of another stellar system, perhaps one from an aging population within the Milky Way known as the thick disk stars.
“I think it is reasonable to conclude that this very high speed impactor came from the population of interstellar objects,” says the University of Arizona’s Kat Volk, who studies how objects shuffle, whiz, and loop through our solar system. “I expect interstellar objects to be common enough—both from theoretical considerations and from the implications of 'Oumuamua—that I think an interstellar origin is the simplest explanation for this bolide.”
A really heavy beach ball
Measuring maybe hundreds of feet across and behaving somewhat unusually, the initial interstellar asteroid ‘Oumuamua prompted some followup study and even provoked speculation, including from Loeb, about whether it might be of artificial origin. But that’s not the case with this newly identified space rock.
At roughly three feet across and weighing in the neighborhood of 1,100 pounds, the meteor was just a fraction of ‘Oumuamua’s size. That means it was nowhere near large enough to survive the journey through Earth’s atmosphere. Having completely disintegrated in the skies just north of Manus Island, it’s too late to study this object and try to determine its composition.
But, Loeb says, such objects are probably numerous, with perhaps 60 sextillion similarly sized rocks launched outward by a single star. If astronomers could find another Earth-bound visitor before it hits our atmosphere, they could gather even more valuable scientific insight by watching its fiery demise.
“If we identified such a thing in real time,” Loeb says, “we could take a spectrum and figure out the composition” as it burns up in Earth’s atmosphere.