Race to examine Earth’s first interstellar visitor.

IT came from beyond our solar system.

Its appearance caused something of a stir.

On October 19, the PanSTARRS 1 telescope in Hawaii detected a faint pinprick of light moving against the night sky.

But the orbit it was following appeared wrong.

Most asteroids and comets in our solar system roughly align along the same ‘plane’ as the planets. It’s a hangover from the age when our Sun began to form out of a swirling cloud of gas and rubble.
But this one was on a deep dive from far above that line.

Over the next few days its positions were carefully plotted. The resulting orbit calculations proved astronomers’ suspicions beyond doubt: this object was coming from beyond our solar system.

This was the first time such an interstellar visitor had ever been identified.

But it was moving fast. And it had only been detected after it flashed past the Sun.

The results of the race to find out what it was has been published in the science journal Nature.

Animation of `Oumuamua passing through the Solar System (annotated)


The strange object was racing back towards deep space.

It wasn’t a comet: no telltale trail of vapour had been seen.

So it was classified an “interstellar asteroid” — and designated 1I/2017U1.

That’s a lot of ‘ones’ — emphasising its status as an astronomical ‘first’.

It was also dubbed Oumuamua — a Hawaiian word meaning “a messenger from afar arriving first.”

“We had to act quickly,” astronomer Olivier Hainaut says. “Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”

Among the telescopes around the world racing to track and observe the rapidly reseeding asteroid was the ESO’s Very Large Telescope.

It was able to pinpoint the orbit to a greater resolution, measure its reflectivity and analyse the spectrum of colours it was bouncing back.

This is where things started to get strange.

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These diagrams show the discovery of interstellar asteroid ‘Oumuamua as it passes through the Solar System, its calculated track and the light sampling that has revealed its nature. Oumuamua is not bound by the Sun's gravity.


Oumuamua was ‘flashing’.

Its brightness rose and fell by a factor of 10 every 7.3 hours.

Astronomers quickly determined why.

“This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,” says astronomer Karen Meech of Hawaii’s Institude for Astronomy.

The cigar-shaped rock calculated to be about 400m long.

It’s a shape never before seen among known asteroids.

“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.”

Its unusual dark red colouring is believed to be the result of bombardment by cosmic rays over the course of millions of years in deep space.

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An artist's impression of the Rosetta orbiter at comet 67P/Churyumov–Gerasimenko. A similar mission to observe the interstellar asteroid Oumuamua is a far more ambitious project.


Oumuamua may be moving fast. But that’s not deterring a group of astronomers who want to seize this opportunity to study something that has originated far beyond our solar system.

They’ve launched an ambitious project — dubbed Lyra — to quickly build a probe and strap it to a fast rocket.

They want to send it chasing after Oumuamua before the interstellar wanderer drifts beyond our reach.

But the interstellar asteroid was already moving at 95,000 kilometres per hour when it was discovered approached our Sun. It’s since accelerated to 138,000km/h due to the ‘slingshot’ effect generated by the Sun’s gravity as it sped past.

It’s likely to pass the orbit of Jupiter in May next year.

This means any mission would have to be assembled fast. And the technical effort involved in placing a probe in orbit around the object would be much more difficult than the 2015-16 visit by Rosetta to Comet 67P/Churyumov-Gerasimenko.

And the probe itself would have to move faster than any other human-made object to catch up. Voyager 1, now itself on the edge of our solar system on a course into deep space, currently holds that honour at 61,300km/h.

But some believe we have the technology capable of propelling a probe fast enough to catch Oumuamua.

“Besides the scientific interest of getting data back from the object, the challenge to reach the object could stretch the current technological envelope of space exploration,” the Lyra project astronomers write.

“Hence, Project Lyra is not only interesting from a scientific point of view but also in terms of the technological challenge it presents.”


Calculations put Oumuamua’s approach as being from the direction of the star Vega in the constellation Lyra.

But that star is not its source.

When the asteroid crossed that patch of space 300,000 years ago — Vega wasn’t there.

This means Oumuamua may have been tossed about by the Milky Way’s gravitational tides for hundreds of millions of years.

Astronomers calculate our solar system receives interstellar visitors roughly once each year. But they’re not easy to find.

They come from unexpected — and therefore unobserved — directions. They move fast. And they’re likely dark from exposure to deep space.

But chances are we’ll soon be finding more.

More and more telescopes are being committed to surveying our skies. And some, such as PanSTARRS, are looking in long-neglected directions.