Astronomers have confirmed that an object that recently passed by our planet is from outside our Solar System — the first interstellar asteroid that’s ever been observed. And it doesn’t look like any object we’ve ever seen in our cosmic neighborhood before.
Follow-up observations, detailed today in Nature, have found that the asteroid is dark and reddish, similar to the objects in the outer Solar System. It doesn’t have any gas or dust surrounding it, like comets do, and it’s stretched long and skinny, looking a bit like an oddly shaped pen. It’s thought to be about a quarter-mile long, and about 10 times longer than it is wide. That makes it unlike any asteroids seen in our Solar System, none of which are so elongated.
Astronomers also think this object — nicknamed `Oumuamua, Hawaiian for “a messenger from afar arriving first”— traveled for millions of years before stumbling upon our Solar System. It seems to have come from the direction of the constellation Lyra, but the asteroid’s exact origin is still unknown. More answers might come soon, as NASA’s Hubble Space Telescope is observing `Oumuamua this week. “Our plan is to look at it through the end of the year, so we can get the very best pass possible and figure out where it came from,” Karen Meech, lead author of the study at the University of Hawaii’s Institute of Astronomy, tells The Verge.
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`Oumuamua was first spotted on October 19th by astronomers working on the Pan STARRS telescope in Hawaii. The telescope is used to scan the sky for objects orbiting near Earth, looking for any that might pose a threat to our planet. But one of the rocks in the latest observations looked as if it might not belong in our neck of the Universe.
The team at Pan STARRS continued observing the object over the next couple of days. Based on their measurements, they were fairly certain that they were watching the first ever interstellar asteroid. Up until then, such a distant visitor had never been seen before, so observatories all over the world started following the object, too, in order to calculate its path and figure out its shape.
Interstellar asteroids are thought to be rejects from other planetary systems. When our Solar System first formed, for instance, the giant planets tossed around all the smaller bits of material circulating around the Sun, some of which landed in the outer edges of the Solar System while others were ejected from our neighborhood completely. These outcasts then traveled through interstellar space, possibly passing by other stars. Conceivably, ejected material from other planetary systems must make their way to our Solar System once in a while, says Meech.
Such interstellar objects are thought to pass through our Solar System pretty frequently, but they’re usually moving too fast, and they’re usually too faint to see. With `Oumuamua, astronomers got lucky: the asteroid entered our Solar System at an angle, coming in close by the Sun, and then passed by Earth on its way out of the Solar System. That gave astronomers the chance to catch it with ground-based telescopes. “I think it’s really neat that we had this visitor, however briefly, and we had a chance to look at it up close,” says Meech.
After it was first spotted, dozens of observatories all over the world continued to follow it over the next week and a half. Speed was crucial, since `Oumuamua is getting progressively farther away and growing fainter every day. “We had about a window of 10 days or two weeks to do anything practical,” says Meech. Through those quick observations, astronomers found that `Oumuamua had large fluctuations in brightness, indicating an unusually elongated, spinning object that makes one complete rotation every 7.3 hours.
Now, `Oumuamua is 124 million miles from Earth, zooming away at 85,700 miles per hour. It passed by Mars’ orbit on November 1st, and will reach Jupiter’s orbit sometime in 2018. Soon, it’ll be too hard to track, even with Hubble. “It’s really getting much too faint to do anything at all,” says Meech.
But in the next few years, we may be able to spot more interstellar objects like `Oumuamua. Once bigger telescopes start to come online, like the Large Synoptic Survey Telescope that’s being built in Chile, astronomers will be able to see even more visiting rocks. “I predict there will be a lot of these detected in the future,” says Meech.
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