Oumuamua: Thoughts About Our Visitor From Another Solar System


In late 2017 there came the interesting news that astronomers had spotted a visitor to our solar system. The first one we have ever seen. This visitor was given the name Oumuamua which is Hawaiian for “messenger from afar arriving first”. It was thought to be an asteroid or maybe even a comet. We know it’s not from our solar system due to the extreme angle (33º) it entered the inner solar system from. As someone who has an interest in astronomy I’ve been keeping a keen eye on the developments of this story as astronomers gain more insights into what it is.

There are some things we don’t know about it. We’re not quite sure of it’s shape. All images we’ve seen of it are artists impressions of what it might look like, such as the picture above. It might be cigar shaped like the picture suggests, but it might also be very thin and more pancake shaped, or it might be a group of objects. We’re also not terribly sure where it came from or how long it’s been traveling around the galaxy in interstellar space. For all we know it could have been traveling for millions of years.

When it entered the inner solar system it came surprisingly close to Earth at 0.1616 a.u. (An astronomical unit is the distance between the Sun and the Earth which is approximately 150 million km or 93 million miles) which means it was around 24.2 million km or 15.0 million miles away at closest approach to Earth on October 14 2017. This may sound a lot but in astronomical distances this is very close. And we didn’t even see it then. We only noticed it sometime later after it had passed us on 24 October 2017. This does make you wonder how many other objects have come this close to Earth and we haven’t even spotted them…

Diagram by Guy Ottewell showing Oumuamua’s path in our solar system.

Before I go any further I would like to state here that there has been some speculation that Oumuamua might be an alien spacecraft of some kind. I will go more into this shortly, but before I do I would like to state that there is no proof of this. Before we can say it’s an alien spacecraft we have to rule out quite a few other possibilities first. The more outlandish the theory the more certain and concrete the proof has to be.

Some scientists began speculating that Oumuamua might be an artificial object quite soon after it was discovered. This was because it was not from our solar system and seemed to be cigar shaped which is thought to be the optimal shape for a craft traveling through space. Since then there has been the thought that it could be more pancake shaped which could then make it a probe or solar sail of some kind. The size of it is thought to be no more than 914 metres by 122 metres  (that’s 3,000 feet by 400 feet), but I’ve seen other estimates that suggest it is smaller than this. In fact it could only be a tenth of this size. As I’m a Star Wars geek I always find it easier to visualise the size of things by finding an equivalent Star Wars ship that is roughly the same dimensions, and 914 metres is virtually the same size as a Victory-class Star Destroyer (you don’t see these in the films but they’re in the Expanded Universe, or Legends as it is known now. For comparison an Imperial-class Star Destroyer, which you see often in the Original Trilogy, is 1,600 metres, or one mile long). I’m not saying it looks like this, it’s just a handy size comparison. So don’t be alarmed 😀

A Victory-class Star Destroyer

Oumuamua began to accelerate once it passed the Sun. For some this seemed to indicate that Oumuamua was actually a comet and the increased speed was due to outgassing created from the frozen material on it. The problem with this idea is that there is no discernible tail to Oumuamua like there is with other comets. However some scientists have also suggested if Oumuamua is something like a solar sail then that might explain the acceleration. The Sun’s radiation from the sunlight creating pressure on the sail would cause it to accelerate. However this is just speculative.

There are some reasons why Oumuamua is probably not an alien spacecraft. Firstly when it was observed it was discovered that it was tumbling from end to end. If it is an alien spacecraft then it would be out of control (or maybe they made it move like this so we wouldn’t be suspicious…). Secondly, aside from the acceleration which may still be explainable as a natural effect, it seems to be at the mercy of gravitational forces in our solar system. Thirdly we have pointed telescopes and radio telescopes at it and found no evidence of transmissions or a power source of any kind. If it is a spacecraft then it is dead or in hibernation mode.

Oumuamua is the first observed visitor from another solar system. It does have some very strange properties, such as it’s size and shape, which have suggested it may be something other than an asteroid or a comet. The problem with this is that we may never know for sure, or won’t know for a long time. Until we can observe Oumuamua up close all we can do is speculate about it. Currently there are no plans to build a probe to investigate Oumuamua and even if we did we currently lack a propulsion system that would be fast enough to catch up with it, but maybe in the future we could. Personally I think it’s an asteroid, but a very interesting one. Yet there will always be a question mark surrounding it.


Further reading:

Oumuamua – Universal Workshop

Oumuamua – Wikipedia

Oumuamua’s Path In Our Solar System – EarthSky

What Is An Astronomical Unit? – EarthSky

What Is Oumuamua? Here’s What We Know About The Interstellar Object – NBC News Mach


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