7 Ways We Might Finally Prove Aliens Exist

4. Pollution

In the search for alien life, at the moment we're pretty much just looking for a race exactly like our own. Something that we definitely know about the human race is that we have a nasty habit of polluting our planet, so who's to say that aliens wouldn't do the same?

Using similar techniques as the one for detecting biosignatures, we could also be able to measure the amount of pollutants in an alien world's atmosphere. Not only would high levels of industrial pollutants indicate that there is indeed life out there, but it would also mean that they were coal burning, trouser wearing, intelligent industrialists too.

Again, we'd have to be sure that it's not just the work of a dirty great volcano, but it's definitely a start. Aside from the cloud of noxious gasses that we merrily pump into the atmosphere, there is also another, very visible form of pollution spilling from our planet: Light.

We currently don't have the technology to do this, but in the future we may be able to develop instruments that could detect strong, artificial light coming from the night-side of an exoplanet. Of course, this relies on the aliens developing light in the first place. We think this is pretty likely, but it would be just our luck to miss out on a hyper-intelligent race of alien beings that were totally blind or something.