Where are the Aliens?

Radio Buzz

Bruno wasn’t the first person to dream of worlds beyond our planet, and he wouldn’t be the last. Works from ancient Greece, Jain scripture, and medieval poetry all speculate the existence of life elsewhere. But it was only in the last century that we were able to turn this conjecture into a science.

Firstly, it’s important to know that we humans are noisy. On a cosmic scale. For the last two centuries, our constant back-and-forth babble via radio communications has projected an ever-growing bubble of buzz and hum around our planet, one that could be detected from elsewhere in the local galaxy. We produce a lot of other interreference, too, but radio waves, especially, are long and low-energy, and they can travel many millions of miles without being disturbed.

Radio signals can be emitted from all sorts of processes, not just intelligent civilisations, but scientists love to listen out for anything that could be interpreted as some kind of alien signature.

The Science of Searching

Dr Frank Drake also worked on the “Pioneer Plaques.” These were engraved messages, bolted to the side of the Pioneer space probes, which were designed to be read by any aliens who might intercept them in their millennia-long lifetimes exploring the wider cosmos.

But Drake is maybe best-known for the “Drake Equation,” which attempted to put a number on the likelihood of alien life existing beyond our world. Coined in 1961, the equation describes N, the number of civilisations in our galaxy that we could communicate with, and goes as follows:

N = R_* • f_p • n_e • f_l • f_i • f_c • L

This may look complicated, but it simply describes the number of factors scientists must consider when looking for extra-terrestrial life. First, scientists must consider R_*, the rate at which stars form. f_p is the proportion of these stars that have planets. n_e is the proportion of these planets that could support life, while f_l is the number of these that actually go on to develop life. f_i is the likelihood that this life is intelligent. f_c and L consider the chances of these species releasing signals into space, and for how many years these signals will be created.

Phew! That was a lot. But the main point is that the Drake Equation provided an outline for astrophysicists to follow, and a list of factors to look for in their cosmic observations. In fact, a few years later the iconic SETI (Search for Extra-Terrestrial Intelligence) Institute was founded, in part to research these very same things.

Aliens in the Solar System

Orbiting our Sun are eight planets. Of these, half are gassy – meaning that they are home to ferocious winds, howling cyclones, and thousands of miles of endless atmosphere with no solid surface underneath to be found. The other half (including Earth) are rocky. But with Mars and Mercury having little to no atmospheres, Mercury and Venus reaching surface temperatures of over 400*C, and all three of these having not a single drop of liquid water, it seems that Earth and Earth alone may be the planet to go to find life in our solar system.

But all hope is not lost! The planets of our local neighbourhood may be mostly hostile and unwelcoming, but there are (at current tallies) 293 moons in our solar system. All of these have solid, rocky surfaces. Some have oceans. Some have atmospheres. Some have geothermal activity and others magnetic fields.

You see, scientists believe that life on Earth may have started some 3.7 billion years ago in the depths of our oceans, where the perfect cocktail of minerals, heat and oxygen came together to form rudimentary organisms. Who’s to say that moons with deep, sub-surface oceans like Enceladus and Europa are any different?

Scientific interest in these moons has grown exponentially over the years, with recent missions including that of JUICE (the JUpiter Icy moons Explorer), which hopes to look closely for signs of life around the ocean-moons Ganymede, Callisto, and Europa.