’Oumuamua … something to phone home about?
Astronomers debate origin of first interstellar object to pass through the solar system. Robert Matthews writes
As Star Wars fans try to contain their excitement over this week’s premiere of The Last Jedi, astronomers are agog at a real-life space drama in our solar system.
The Earth has just had its first known encounter with an object from another star – and there is talk it may have been an alien spacecraft.
The drama began in mid-October, when astronomers in Hawaii detected an object about 33 million kilometres from Earth.
At first it seemed like just another chunk of debris left over from the creation of the planets but as more data came in, astronomers realised the object was like nothing else they had seen.
Plotting out its path, they found it had swooped in from the abyss of space in early September, shooting past the Sun at 315,000kph and was heading back out of the solar system.
Their calculations revealed that it was on a hyperbolic trajectory, unlike the elliptical paths of ordinary comets and asteroids.
That means the Sun’s gravity has never been able to hold on to the object, which must have started its journey in another star system.
This makes 1I/’Oumuamua, as the object is now officially called, the first known visitor from interstellar space.
But astronomers had another surprise when they turned some of the world’s largest telescopes on to the object.
They were expecting it to be a kind of comet, but ’Oumuamua appears to be something different.
Despite shooting past the Sun closer than the planet Mercury, it showed no sign of melting in the heat and lacked the bright tail of a comet.
Instead, analysis of the sunlight bounced off its surface reveal ’Oumuamua to be deep red in colour, consistent with long exposure to cosmic rays in deep space and sometimes seen on asteroids.
But the mystery deepened once more when data revealed that ’Oumuamua is shaped like a long cylinder, between 200 metres and 400 metres long and about a 10th as wide. No known comet or asteroid has such a shape.
As science-fiction buffs quickly pointed out, however, there are striking similarities between ’Oumuamua and the centrepiece of the 1973 novel
Rendezvous with Rama by Arthur C Clarke, author of 2001: A Space Odyssey.
In the novel, astronomers detect what they think is an asteroid plunging through the solar system at very high speed, only to discover that its trajectory indicates a starting point among the distant stars.
They then discover that the object, named Rama after the Hindu deity, is cylindrical in shape.
The parallels with ’Oumuamua are not perfect. In the novel, Rama is far bigger at more than 50km long, stubbier and spins rapidly to provide artificial gravity within its capacious interior.
But that hasn’t deterred speculation that the newly-found object is also an alien starship.
And why not? Many scientists are perfectly happy with the idea that aliens exist in our galaxy, but ask them if aliens might be present in the solar system and the question will be met with howls of derision.
The double-think is partly the result of scientists wanting to keep their distance from the endless, wild-eyed claims that UFOs sightings are proof of alien visits.
A standard put-down is that even travelling at the speed of light, it would take thousands of years for an object or a craft to cross the galaxy. This also presumes knowledge of the technology available to aliens.
The fact is there are no knock-out arguments against ’Oumuamua being an alien spacecraft but there is a pretty strong reason not to roll out the red carpet for ET any time soon.
It is based on a mathematical method for making sense of evidence, known as Bayes’s Theorem.
This shows we should only get excited about the object being an alien spacecraft if its characteristics are incredibly hard to explain on the basis of any other possibility.
And on the basis of what we know of ’Oumuamua so far, which is not very much, that is not the case.
Of course, that would change dramatically if astronomers detected, say, signals coming from the object or found antennas or other evidence of alien handiwork.
In Clarke’s novel, astronomers resolve the mystery of Rama by sending an unmanned probe to photograph it, revealing its alien nature.
There has been talk about doing the same for ’Oumuamua but unfortunately it seems it is too late for that. Calculations by Nasa experts suggest the object is travelling too fast to be intercepted using conventional rocket power.
By the end of this month, ’Oumuamua will be beyond the reach even of the world’s most powerful telescopes and its true nature will remain forever unknown.
Maybe we should hope it was just an inert chunk of rock. Better that than ’Oumuamua lives up to its Hawaiian name – “Scout from the distant past” – and returns accompanied by a Death Star from a galaxy far, far away.
The object invites comparison with an Arthur C Clarke novel, but astronomers are not keen on alien traveller theory