Ever since it was realised that the stars are other suns, people have wondered whether any of them are accompanied by planets, or ‘exoplanets’ as we now call them. Speculation along these lines were among the charges that led to Giordano Bruno being burned at the stake in the year 1600. It is only since the 1930s that astronomers seriously thought they had the observational tools to be able to find out.
Proving to be both varied and fascinating, moons are far more common than planets in our Solar System. Our own Moon has had a profound influence on Earth, not only through tidal effects, but even on the behaviour of some marine animals. But how much do we really know about moons?
NASA’s New Horizons probe swept past Pluto and its moons at 17 km per second on 14 July. Even from the few close up images yet beamed back we can say that Pluto’s landscape is amazing. Charon, Pluto’s largest moon, is quite a sight too, and I’m glad that I delayed publication of my forthcoming Very Short Introduction to Moons so that I could include it.
World Space Week has prompted myself and colleagues at the Open University to discuss the question: ‘Is there life beyond Earth?’ The bottom line is that we are now certain that there are many places in our Solar System and around other stars where simple microbial life could exist, of kinds that we know from various settings, both mundane and exotic, on Earth. What we don’t know is whether any life DOES exist in any of those places.