Photo: Pixabay One of my favourite science fiction novels is Rendezvous with Rama, written by Arthur C. Clarke in 1973. In the story, our telescopes detect an object moving into the inner Solar System at a speed too high for it to be orbiting the Sun.
It is a visitor from interstellar space. In addition, it is not something roughly spherical, it is a huge, rotating cylinder. With great difficulty a spacecraft rendezvous with it, and discovers it is an interstellar spacecraft.
It is rotating to provide artificial gravity for those inside. Fears of an imminent alien invasion are dispelled when the space ship flies by the Sun and heads back out into the gulfs between the stars, on a journey taking thousands, or tens of thousands, of years. On Oct.
19, 2017, the Pan-STARRS telescope in Hawaii picked up a faint object moving inward into the Solar System. It was moving far too quickly to be orbiting the Sun, which meant it was coming in from interstellar space. However, unlike the object in the story, this one was not an alien spacecraft.
At first, scientists thought it was a comet, a lump of dirty ice, similar to the comets that are members of our Solar System. Out on the edges of the Solar System, where it is very cold, there are lots of lumps of rock and dirty ice left over from the birth of the Sun and planets. These lumps contain bubbles of gas and various volatile organic chemicals.
However, out there it is very cold, so all these ingredients can remain undisturbed for billions of years. However, on occasion a collision or close encounter between two of these lumps will throw one onto a new orbit taking it into the inner Solar System. The other might be thrown out of the Solar System altogether, possibly to wander space for millions or billions of years before it passes close to another star.
The one moving inwards encounters increasing solar heat. Its volatile chemicals start to evaporate. In the vacuum of space, the ice turns directly into water vapour.
A lump of dirty ice a kilometre or two in size does not have much gravity, and as the materials gluing it together evaporate, dust and gas from its surface wander off into space. This forms a glowing tail millions of kilometres long, turning a lump of dirty ice into a comet, one of the most beautiful things in the sky. This mysterious object speeding into the Solar System showed no sign of evaporating volatile chemicals.
It was behaving more like an asteroid, so it received a name. Because it was discovered using a telescope in Hawaii, it received a Hawaiian name, Oumuamua, Hawaiian for "our first visitor from afar". It was not even roughly spherical.
It was between 100 metre and 1,000 metres long, and 15 metres to 167 metres in its other dimensions (width, thickness or perhaps diameter). Rather than rotating, the object appeared to be tumbling, which is typical of irregularly shaped asteroids. So the current idea is it is an asteroid that was ejected from its system by a collision or close encounter with another asteroid or planet.
There have been attempts to find out what star system Oumuamua may have come from. It has been suggested it came from the direction of Vega, a bright, bluish white star high overhead this time of year. This star lies some 25 light years away.
Oumuamua was moving at about 90 kilometres per second. If it had come from the Vega system, it would have taken almost 90,000 years to get here. It is possible it has nothing to do with Vega and has been drifting in space for millions of years.
A big question is how often we have interstellar visitors. At the moment we don't know, because we only recently developed the technology for detecting them, and maybe only just as recently learned we should look for them. It was a real shame we didn't have the space technology to go have a really close look at this traveller.
••• • Saturn rises at sunset and Jupiter around midnight. • Venus is vanishing in sunset glow. • The Moon will be full on Aug.
19. This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet..
