Let's be frank. Even to an optimist, the chances of finding life on Mars - always the greatest hope - now seems slim. Most of the current research involves looking for fossilised life of the most basic level on Mars, for example, the nodes in the meteorite of Martian origin, ALH84001. So where do people now turn their attentions? Well, the best answer in the solar system would be Europa.
What is Europa?
Not the place with Paris and London, that's Europe. It's one of the four big satellites of Jupiter, and it's called... Europa. These moons discovered by Galileo Galilei in 1610 (hence their name as the Galilean Moons) are so massive that they are comparable in size to the planets Mercury and Pluto. Europa is the smallest of these, about the size of our own moon.
Why Could there be Life There?
Life, as we know it, operates on a limited set of chemical reactions1, the most basic of which rely on the presence, if not the actual participation, of liquid water. We know Europa is covered in ice. But what's underneath? The physical data that we have for Europa suggests one of three possible structures:
- Ice all the way down
- Slushy ice
- Liquid water
Earth has liquid water - it has life. Europa may well have water; so Europa may have life.
But Why is that Important?
If we discover that there is life out there, think of the philosophical issues it raises. For religious people, there's no mention of it in the Bible, Koran or any other religious book or teachings, so this may call into question humanity's whole belief structure.
Scientifically, if we find life there it gives us more data on the frequency of life, which is useful for determining the frequency of civilised life 'out there' using the Drake Equation.