Our first-ever interstellar visitor has been sighted

Enlarge Image This artist's impression shows Oumuamua an interstellar asteroid.                  ESO  M. Kornmesser

Enlarge Image This artist's impression shows Oumuamua an interstellar asteroid. ESO M. Kornmesser

When the trajectory data was confirmed with the European Space Agency's telescope on Tenerife in the Canary Islands, it turned out that the asteroid or possible comet had its origins many light years away from the Solar System.

The astronomers believe that instead, the object could have been traveling through our home galaxy, the Milky Way, for hundreds of millions of years, without being attached to any star system, before reaching us. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of today's Solar System, but until now there has been no way to tell if our Solar System is typical. This suggested that the object was likely highly elongated. Gemini, the ESO's Very Large Telescope in Chile, the Canada France Hawaii Telescope, the United Kingdom Infrared Telescope, and other observatories trained their eyes on the asteroid. Ultimately, the visitor will need a name, and rules do not yet exist for naming such extra-solar system guests.

Combining images from the various telescopes, an worldwide team found that the asteroid varies in brightness by a factor of about 10 every 7.3 hours, matching its spin about its axis.

The quarter-mile object is believed to be around 10 times as long as it is wide, a ratio "greater than that of any asteroid or comet observed in our solar system to date", NASA said. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.

'Oumuamua is likely made up of rock and possibly metals, and does not hold any ice or water as a comet might, NASA said. It is estimated to be at least 400 metres long.

The time frame is important because backtracking the path of 'Oumuamua indicates that it came from the direction of Vega in the constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago.

That has led scientists to speculate that the asteroid is an interstellar wanderer that has stumbled across our solar system. This unique object was discovered on October 19, 2017 by the Pan-STARRS 1 telescope in Hawaii. "And now that we have found the first interstellar rock, we are getting ready for the next ones!" "It's a unusual visitor from a faraway star system, shaped like nothing we've ever seen in our own solar system neighborhood". The object is the first to be named an interstellar asteroid, officially designated A/2017 UI by the International Astronomical Union, which created the category after it was discovered. The correct forms for referring to this object are now: 1I, 1I/2017 U1, 1I/'Oumuamua and 1I/2017 U1 ('Oumuamua). So, the name should sound like H O u mu a mu a.

"Certainly this is a new type of object".

The observations and analyses were funded in part by NASA and appear in the November 20 issue of the journal Nature.

The object was discovered by Canadian astronomer Robert Weryk at the University of Hawaii Institute for Astronomy.

Astronomers will continue to make observations of the object before it slips back into darkness.

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