Aliens! Where are they all? The Fermi Paradox, originated in 1950, can basically be summarized as “if alien life in the universe is so likely, where the hell is it?” (the original paradox was elucidated in more scientist-like language but we got the general gist of it here). Well, to answer this question, here are some possibilities – and they are surprisingly closer to home than you might like.

Let’s start with…

5. Europa

2010: Odyssey Two was hardly the best entry in the A Space Odyssey series (did you know there are four books in the series and only the first one has anything to do with what’s going on in the film series? We did and we are very sad about it). Anyway, 2010 and its sequel, 2061, involve the possibility of alien life on Europa, which has long been known to have an ice-covered surface that is really, really smooth. We can’t overemphasise how smooth the surface of Europa is. In an area of space where other moons are covered in craters from meteor impacts, Europa doesn’t show any evidence of impacts.

Why doesn’t it show evidence of meteor impacts, you might wonder. Is it because Europa has somehow never been hit by a meteor in the millions of years it has been floating around Jupiter? No, of course not. It doesn’t show impacts because something keeps melting the ice on its surface, which then flows like water does on Earth and re-solidifies into a fresh, new and above all, smooth, icy surface.

In astronomical terms, Europa is as smooth as a cueball (but not quite as easy to accidentally pocket).

Europa has liquid water on it, is what we are getting at here; and it’s salt water, from what we can tell. That means it’s relatively warm and it has an environment similar to the one on Earth where we believe life first evolved. The ice-coated surface of Europa also gets around another big problem that alien life in our solar system will face, which is a lack of a significantly dense atmosphere to keep life safe. It’s like Europa has a giant sea on it with a giant dome protecting it.

Oh and just one more thing: what there is of Europa’s atmosphere is made of oxygen – pure oxygen (so don’t rock up there and light a cigarette unless you want the entire place to explode). I wouldn’t recommend trying to breathe it because it’s pretty thin but it’s oxygen, the element almost every single life form on Earth requires in order to live. Basically, Europa is the perfect for alien life to evolve.

But here’s the thing: Europa isn’t even the only moon in our solar system that might support alien life, so let’s leave this potential holiday destination in the stars alone for now and check out its distant neighbour…

4. Titan

If there was one place in the universe that you wouldn’t expect to find alien life, it’s probably your sock drawer but if you had two guesses, the second one might well be Titan. This Saturnian moon (named after the mythical creatures from Ancient Greece because astronomers have a thing going on for what they call these distant rocks) boasts epic views of the ringed planet, or at least it would if you could see through the orange atmosphere. What’s causing Titan’s atmosphere to appear orange? Well, that would be a lovely mix of nitrogen and organic materials.

Yes, you read that right. Titan has organic material on it. Specifically it has methane and ethane; two chemical compounds that bacteria on Earth absolutely adore. Also, this means Titan probably smells of farts, which we here at All Over the House consider an unexpected bonus because we refuse to grow up (and you can’t make us, Dad!).

Titan also spends most of its orbit within the magnetosphere of Saturn, which is a big deal in terms of making life possible according to the rules we know from studying life on Earth. Here on Earth we have a massive magnetic field generated within the planet, which prevents our atmosphere and all life on the planet being ripped away by the solar radiation equivalent of blasting your driveway clean with a high-powered water cannon. So although Titan is pretty cold, it has organic materials present and it gets shielded from potentially deadly radiation. That’s a lot of ticks on the “life might evolve here” checklist right there.

But it’s not even the coldest place in the solar system where we might find life cropping up. For one very surprising entry, we need only glance over at…

3. Pluto

The not-a-planet that was once a planet which floats about so far away from the Sun that human civilisation was tens of thousands of years old before we even noticed it was there might seem like an odd location to be looking for signs of life but here we are. Pluto, the frozen world from where the Sun looks like a particularly large star in the perpetually-night sky has some interesting features that could see life evolve there.

For a start, Pluto has a large sub-surface ocean that’s not too dissimilar to Europa. Pluto also has an atmosphere with methane and nitrogen in it, which makes it not unlike that of Titan (and also means that our solar system really does seem to smell of farts a lot. It’s no wonder aliens haven’t visited us, the solar system stinks).

Speaking of the Plutonian atmosphere, it’s worth noting that about 19,000 years ago, some of its atmosphere was pulled away and landed on its largest moon, Charon (which has a crater on it named after Princess Leia, by the way. That has nothing to do with life in the universe, we just thought you’d like to know). What was in the atmosphere at the time? Tholins.

Now you’re probably wondering what the King of the Dwarves from The Hobbit is doing way out on the edge of the solar system and to that we say, stop being silly for a minute. Tholins (which are different from Thorin because the spelling isn’t the same and that’s how you can tell) are chemicals that are surprisingly common to the moons and planets on the outer rim of the solar system. They are organic compounds that react with water under certain circumstances and form the basis for prebiotic chemistry. That’s really, really important because “prebiotic chemistry” is a long, sciency way of saying these are the chemicals life emerged from.

Suddenly, having that large, sub-surface ocean is looking a lot more interesting, isn’t it? Good old Pluto might turn out to be a destination worth making the incredibly long trip to after all.

Anyway, let’s bring things a bit closer to home now; because all this talk about cold, cold planets is making me feel chilly. How about we visit…

2. Mars

Good old Mars! The Red Planet has long been thought to contain alien beasties so it’s only natural that it shows up on this list. Mars is a weird case amongst the contenders we’ve taken a look at so far however, because it’s barely outside of the habitable zone our Earthly scientists worked out as being the perfect location in the solar system for life to almost certainly evolve (Earth is right in that zone by the way, so if you were wondering why we are here, that’s a big reason). Mars is also very big – not Earth big, but big – and it used to have a much thicker atmosphere; which it’s now slowly losing because Mars is a bit absent-minded like that and keeps leaving things behind while it wanders through space.

Its atmosphere isn’t the only thing Mars has lost over the millennia, either. It used to have its own magnetic field, which it then proceeded to lose because apparently planets can do that and if you’re worried that the same thing might happen to Earth, you absolutely should be. Earth’s magnetic field fluctuates over time and nobody knows why so it’s possible, albeit rather unlikely, that if you pop back in a few million years’ time, it might not be here any more. You’re probably fine for the moment, though.

Mars lost its atmosphere when the magnetic field went, for similar reasons to why Titan is able to hold onto its atmosphere: magnetic fields deflect solar radiation and it’s the battering by solar radiation that strips a place of its atmosphere. Mars also used to have running water on its surface; a climate; a decent temperature; and… organic compounds inside rocks.

Basically, Mars in the past was like Earth’s little brother. We can’t say for certain that Mars had life crawling around on its surface in the distant past but it had pretty much everything you needed to cause life to emerge so if there’s anywhere in the universe that might have evolved life, Mars seems like our best bet.

Well, almost. There is one other place we should probably start looking if we want to find life…

1. Earth

No, I’m not talking about those weird neighbours that you could swear don’t quite look human (although don’t rule them out…). Life evolved on Earth and developed into an immensely complex and wildly diverse range of species. We have the octopus, for example – and nobody can look at one of those things without thinking they seem pretty alien because they are. They split off from the rest of us so far back down the evolutionary family tree that they are practically as close to aliens as we can expect to find in a distant relative.

The existence of such a vastly-separated species living in our oceans has given rise to a number of theories of just what else might be lurking in the dark corners of the seas. There is a huge amount we don’t yet know about the deep oceans of the Earth, which means there is a very good chance that even more distant ancestors are lurking down in the murky depths. Creatures that split off from the evolutionary tree as we know it at a date even earlier than the octopus’ distant ancestors could be floating around near underwater volcanoes right now; and we wouldn’t even know it. These creatures might not be technically alien (because they would, y’know, have come from the same original source as us) but they would be so distantly related that they may as well be.

The thing is, that’s not even the strangest part of finding alien life on Earth. Have you ever stopped to wonder why scientists think all life on Earth can be traced back to a common ancestor? Well it’s because we all share the same fundamental building blocks of life. All life as we know it contains DNA and RNA. These are the fundamental “building blocks of life” as we know it. It’s how our cells get their instructions. It’s how we get built.

So what if there’s a species on Earth that evolved on Earth but which doesn’t have any DNA? Welcome to the oddity of science known as shadow biology. A number of scientists have now proposed that, since we detect life by studying ribosomes, any species that doesn’t have any ribosomes will naturally be overlooked. There could be RNA-based life all around us, just wandering about without any DNA at all, and our scientists wouldn’t spot it.

Maybe instead of looking at things that don’t have any DNA, we should be looking at things that have a different kind of DNA; like creatures which use arsenic to generate their amino acids (we don’t use arsenic, we based ours on phosphorous because humans love explosions even on a genetic level).

Phosphorous! You’re made from it!

The possibilities aren’t exactly limitless but they are great in number and this could be a very interesting line of scientific inquiry because it vastly expands the number of moons and planets which could support life that is vastly different to our own.

Now we have to say this: shadow biosphere research is heavily criticised because of its science fiction-like qualities (I mean come on, we are practically talking about searching for the microbe equivalent of Vulcans here) but we may already have discovered the first shadow biology species already. There’s a substance called Desert Varnish, which has been known about since the Victorian era and nobody can adequately decide whether it’s a life form or not. Since Desert Varnish exists in Africa (and on Mars, by the way) we could have literally evolved alongside it and not even noticed our alien neighbours since the dawn of history.

Makes you think, doesn’t it?