Searching for life elsewhere in the Universe is a fascinating endeavour. It is is not a recent idea either. Astronomers in the 1800s used telescopes to search for signs of life and even civilization elsewhere in the Solar System. Some even believed they saw signs of intelligent life on Mars in the form of a grid of canals across the Red Planet’s surface. Illustrations and maps of Mars published by NASA as late as the early 1960s still showed these. Disappointingly, visits to Mars by space probes from the mid-60s onwards revealed it to be more barren and inhospitable than previously thought. There is still a possibility that life arose on Mars billions of years ago when conditions on the planet were milder, and perhaps some bacteria-like organisms cling on to life under the surface. We probably will not know if this is true or not until people travel to Mars to explore.
Elsewhere in the Solar System, there is evidence for oceans of water under the icy surfaces of Jupiter’s moon Europa and Saturn’s moons Enceladus and Titan. These may be the best prospects for life-bearing sites in the Solar System. Could bizarre aquatic life swim in the inky depths of these alien seas? Given the difficulties of sending a mission to drill through the crusts of these distant moons, these will probably not know the answer for centuries.
No one seriously expects there to be intelligent life elsewhere in our Solar System, to find talking and technological folk we have to look beyond. Since 1995 astronomers have discovered 400 or so planets orbiting other stars. The vast majority so far discovered are huge gas giant planets like Jupiter or Saturn but as technology improves we ought to find worlds more like Earth. To find life out there all we can do at present is try to listen for radio signals from alien beings. This is the Search for Extra-terrestrial Intelligence (SETI) and is conducted mainly as a spare-time project by some astronomers. At present no government funds SETI research, but private groups such as the Planetary Society have paid to scan the sky for artificial signals. Grandest of these efforts is the Allen Telescope Array, 42 (to be expanded to as many as 350 eventually) linked 6 metre radio telescopes funded by Microsoft billionaire Paul Allen.
We humans have sent our own messages into space. Plaques and discs of data were been bolted to the Voyager and Pioneer deep space probes should any space travelling ETs find them. Radio messages have been broadcast too, notably the Arecibo Message sent to the Hercules Cluster in 1974. It consisted of 1679 zeroes and ones transmitted in 169 seconds which could be decoded to yield a somewhat abstract-looking diagram (above) giving details of human biology and a map of the Solar System and other useful facts.
Many astronomers would say that alien life is a possibility, but one astronomer, Frank Drake, has tried to work out the number of extraterrestrial civilizations active in the galaxy. The Drake Equation uses estimates of how common planets are around other stars, how many are suitable for life, on how many actually develop life and so on to give, N, the number of alien civilizations. Unfortunately, most of these values are little more than guesses at the moment, so values of N vary from hundreds of thousands to just 1 (just ourselves!)
Perhaps the Cosmos is full of life or perhaps we are alone. Either possibility has awe-inspiring implications.