Is There Life Out There?

by Hamish McGuire

(from Close Encounters of the Third Kind)

Is there the possibility of life on other planets other than our own? The only life we have ever known has been on a single planet, in the entire universe.  How likely is it that there is life out there, somewhere in the vast expanse of space? Would it just be simple, unicellular life like that of bacteria, or more complicated organisms, resembling plant life, or perhaps sentient life more intelligent than us. Well, if we were to look for any signs of life, where would we look?

What about our neighbours, the planets with us in the solar system? What might come first to mind is Mars. Life has always been speculated to have existed on Mars, even if it’s not there now. Liquid water can be found in low volume brine on Martian soil, but life, not even bacterial life has been discovered in it. But what about a long time ago, say hundreds of millions of years ago, when Mars’ climate was much like Earth's, when it had warmer, wetter, climates. Certainly there’s the possibility that life could have existed, even if just primitive. Currently, ancient life is being searched for by rovers such as curiosity and opportunity in potentially ancient habitable locations.

So, no life on Mars. Venus? No, a temperature of 500C and atmosphere pressure of 100 times that of Earth’s wouldn’t allow for it. Maybe microorganisms in the acidic upper layers of Venus’ atmosphere though. Jupiter? No, intense gravity and radiation wouldn’t allow for it, besides the fact it’s a gas giant. But who says life has to exist on a planet? And so we look to Europa, a moon of Jupiter. Europa is very interesting; beneath its icy surface is liquid water. Hydrothermal vents on the bottom of the ocean if they exist, may warm the ice and could be capable of supporting microorganisms, if they don’t exist beneath the ice already. Europa is humanity’s best bet of finding life in the solar system.

However, if we want to look for life, it’s almost certain we would find it on extrasolar planets, most likely orbiting a sun in the goldilocks zone. Since 1992, over 4000 exoplanets have been discovered, ranging in size from that of terrestrial planets similar to Earth's size to that of gas giants larger than Jupiter. The Kepler space telescope has also detected a few thousand candidate planets which may hold life, of which about 11% may be false positives. There is at least one planet on average per star. About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone, with the nearest expected to be within 12 light-years distance from Earth. Assuming 200 billion stars in the Milky Way, that would be 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if red dwarfs are included. The rogue planets (planets with no star to orbit) in the Milky Way possibly number in the trillions.

If there are billions of planets, in habitable locations, with the possibility of supporting life,  why haven’t we been visited by them? Well, maybe they’re out there, but haven’t discovered us yet, or maybe they’re getting to us currently, or maybe they know of us, but have decided we aren’t significant enough for them? Unlikely. On earth, we send out radio messages constantly, firing them into open space in the hope that some civilisation will have the technology to receive it, understand it, and reply to it. Granted the nearest possible habitable planet for humans and plant life (a surface temperature of 22C), Gliese 832 c is more than 15 light years away. That’s well more than 400,000 earth years to traverse at suitable speeds. Nevertheless, if we receive a message from extraterrestrial life, should we answer back? As Stephen Hawking said ‘’meeting an advanced civilization could be like Native Americans encountering Columbus’’.

Maybe, it’s in humanity’s best interests to remain alone in the universe, no matter how likely the possibility of life is.