First-known interstellar asteroid is a unique and shaped like a cigar

Since mid-October, the astronomy community has been buzzing about what might be our Solar System’s first confirmed interstellar visitor. An automated telescope spotted an object that appeared as if it had been dropped on the Solar System from above, an angle that suggests it arrived from elsewhere.

Now the astronomers have confirmed that the object 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 neighbourhood 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 cigar.

It’s thought to be about a quarter-mile long, and about 10 times longer than it is wide. That makes it unlike any other 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”— travelled 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.

Interstellar asteroids are thought to be rejects from other planetary systems. When our Solar System was 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 neighbourhood completely. These outcasts then travelled 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.

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.

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.

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.

with inputs from the Verge