What secrets lurk in the plethora of planets?
The real wonder of our age is this: you can go onto the Web, type in 'PlanetQuest New Worlds Atlas', 'Extrasolar Planets Encyclopedia', or 'Nasa Star and Exoplanet Database', and access the data on 340 new planets that have been discovered in the past five years.
That number is set to grow very fast. Last Saturday, Nasa successfully launched the Kepler telescope, which will find many more planets, including potentially Earth-like ones. It will stare unblinkingly at an area of space containing about 100,000 'near' stars, watching for the tiny dimming of a star that happens when one of its planets passes between the star and us.
Just 10 years ago, we still didn't know whether it was normal for a star to have planets. Maybe planets were very rare, and life a thousand times rarer, and we were the only intelligent life in the galaxy. That always seemed pretty unlikely, but you couldn't prove otherwise.
We now know that planets are as common as dirt. New techniques that can see past the blinding glare of the parent star to pick out only the faint light reflected from a planet's surface have found them around more than a hundred nearby stars.
The telescope mechanises the process. If any of those 100,000 stars have planets that orbit in a plane that causes them to pass between the star and us, Kepler will spot them. Thousands of the stars probably have planets orbiting in that plane, so the tally of 'exoplanets' (planets orbiting other suns) is going to rise very fast.
Even in that tiny section of sky, Kepler will probably miss tens of thousands of other planets. Moreover, the great majority of the planets it does find will be gas giants like Jupiter and Saturn, which are the easiest to spot. But the real triumph is finding planets like Earth.
The most likely candidate so far is a planet called Gliese 581c. It's the middle planet of three orbiting Gliese 581, a star about 20 light-years from here. It is a rocky planet, not a gas giant, and is in the 'goldilocks zone' around its star where the temperature permits liquid water on the surface.
We still cannot see if it has an atmosphere and, if so, whether it contains the telltale gases that indicate the presence of life, but a new generation of orbiting observatories planned for the next decade could give us the answers.
Two big consequences are going to come out of this. One is a long and tempting list of Earth-like planets in our own stellar neighbourhood. It's quite likely that there will be evidence of life on many of them.
The other consequence is a huge question about intelligent life in the universe. If planets capable of supporting life are so commonplace, then where is everybody?
Is intelligence a rare accident in the evolutionary process, or such a self-destructive attribute that intelligent species don't usually survive more than a couple of centuries after they industrialise? Are they all observing radio silence because there is something dreadful out there? Or have we just not figured out yet how mature galactic civilisations communicate?
Gwynne Dyer is a London-based independent journalist whose articles are published in 45 countries
