Quirks & Quarks

'For the first time ever, we have a piece of another star system,' astronomer announces

The asteroid's shape and the speed at which it travelled are clues that it came from another solar system.
This artist’s impression shows the first interstellar asteroid, `Oumuamua. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was travelling through space for millions of years before its chance encounter with our star system. It seems to be a dark red highly-elongated metallic or rocky object, about 400 metres long, and is unlike anything normally found in the Solar System. (M. Kornmesser/ESO)

This past October, astronomers were in for a pleasant surprise when an object from a distant star system passed by Earth.

It was the first sighting of an interstellar object in our Solar System, initially located by the Pan-STARRS1 telescope in Hawaii. The object was later determined to be an asteroid and was given the name Oumuamua, which is Hawaiian for "a messenger from afar arriving first."

Joining us to discuss the monumental discovery and its significance is Dr. Karen Meech, who led the observation efforts. She's an astronomer at the University of Hawaii's Institute for Astronomy. 

What's ​the​ significance​ of​ this ​sighting?​

"For the first time ever, we have a piece of another star system," said Meech. 

Where ​did ​the ​asteroid come from?

Meech said it came from the direction of the bright star Vega, in the northern constellation of Lyra, and that it's been travelling around the Milky Way for millions to billions of years. 

Its trajectory and speed demonstrated that it clearly came from outside our solar system. Basically, the high speed at which the asteroid is traveling through the solar system cannot be due to acceleration from the Sun's gravity alone. This object must have approached our solar system already with considerable initial speed. It is simply traveling too fast to have originated in our solar system.

The object's high speed also means that the Sun's gravity cannot slow it down enough to keep it bound to our solar system. The object will leave, and end up with about the same speed with which it entered; only its direction will have

This diagram shows the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Unlike all other asteroids and comets observed before, this body is not bound by gravity to the Sun. It has come from interstellar space and will return there after its brief encounter with our star system. Its hyperbolic orbit is highly inclined and it does not appear to have come close to any other Solar System body on its way in. (ESO/K. Meech, et al.)

How ​fast​ was​ it ​travelling?

The asteroid's cruising velocity through interstellar space was 26.3 kilometres per second. That was its speed as it approached our solar system, and the speed it will have after it exits our solar system. At that speed, the asteroid will cover one light year in about 11,000 years. 

What​ did ​the​ asteroid ​look ​like?

It was a rocky, cigar-shaped object with a somewhat reddish hue. It's up to 400 meters long and highly-elongated, perhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike asteroids seen in our solar system, it may provide new clues into how other solar systems formed.

Regarding its composition, observations suggest this object is similar to many asteroids found in our solar system dense, possibly rocky or even metallic. The object's surface is somewhat reddish due to effects of irradiation from cosmic rays over millions of years.

Where​ will ​it ​go ​next?

As of November 20, its location is approximately 200 million kilometres from Earth, the distance between Mars and Jupiter though its outbound path is about 20 degrees above the plane of planets that orbit the Sun. The object passed Mars's orbit around November 1 and will pass Jupiter's orbit in May of 2018. It will travel beyond Saturn's orbit in January 2019. As it leaves our solar system, Oumuamua will head for the constellation Pegasus.