‘Oumuamua: All you need to know about the mysterious alien asteroid that has scientists very excited

By Nilima Marshall

Asteroids brushing past Earth are more common than you think but there is something special about ‘Oumuamua – the recently discovered large interstellar rock.

Unlike other asteroids previously spotted, astronomers are certain that this mysterious object, which was detected hurtling past our sun last month, is actually from another solar system.

Here’s everything you need to know about this celestial wanderer:

Where did ‘Oumuamua come from?

Based on its trajectory, astronomers initially believed ‘Oumuamua travelled from another star called Vega, which is 25 light years away in the constellation of Lyra.

However, the journey is estimated to have begun 300,000 years ago, and at that time, Vega was located in a different position.

This led scientists to speculate ‘Oumuamua is an interstellar traveller, originating somewhere outside of the solar system.

Dr Karen Meech, from the Institute for Astronomy in Hawaii, said: “‘Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the solar system.”

What does it look like?

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Travelling at the breakneck speed of 59,030 miles per hour (95,000 kph), ‘Oumuamua is a cigar-shaped rock about 400 metres (1,312ft) long.

Astronomers believe the asteroid to be a dark, reddish colour.

They realised ‘Oumuamua had an elongated shape after telescope observations showed the asteroid’s brightness changed dramatically as it span on its axis every 7.3 hours.

Dr Meech said: “This unusually large variation in brightness means that the object is highly elongated: about 10 times as long as it is wide, with a complex, convoluted shape.

“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.”

How did scientists find it?

Pan-STARRS 1 – a telescope in Hawaii designed to find near-Earth objects – spotted the asteroid on October 19.

‘Oumuamua was seen as a faint point of light moving across the sky.

With the asteroid quickly fading away from view, astronomers had to work quickly to collect data and other telescopes, including the European Southern Observatory’s (ESO) Very Large Telescope in Chile, were put into action to study the object in greater detail.

Interstellar asteroids are believed to pass through the inner solar system once a year but are generally very difficult to spot, which makes ‘Oumuamua pretty special.

So why the unusual name?

‘Oumuamua is a Hawaiian word which means a messenger or scout.

Pronounced Oh-moo-ah-moo-ah, the first character is a Hawaiian ‘okina, not an apostrophe. The name was chosen by the Pan-STARRS team based in Hawaii.

What is ‘Oumuamua made of?

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Data from the telescopes suggest ‘Oumuamua “is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice”.

Astronomers believe its surface may have been darkened and reddened by the impact of cosmic rays over millions of years.

Dr Olivier Hainaut, from the ESO in Garching, Germany, said: “We are continuing to observe this unique object, and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy.”

The findings are reported in the journal Nature.

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