In Part I, we discovered that there are probably at least 20 billion trillion planets in the observable universe. So, trying to find life might seem a sure thing. But how could we identify an exoplanet that shows evidence of at least sustaining life? Even before we reach that point, how do we identify an exoplanet when it is so far away?
One of the ways is to monitor the light of the star we are investigating. We can be very accurate in this. If the light level should dim ever so slightly and a little time later, resume its original luminosity, we may assume a planet has passed in front of the star and our observation of it. Multiple planets can be discovered this way.
Recently, with the launch of the James Webb Space Telescope or JWST, we are able to analyse the atmosphere of some of these planets and calculate how far they are away from their star. What astronomers are looking for is whether an exoplanet is orbiting within what is called the “Goldilocks Zone”. This is an orbit which allows the planet to be neither too hot nor too cold to sustain life as we know it. To date, we are finding many such planets. Those that show the right sort of chemical signature in their atmosphere excite astronomers even more. This is an ongoing search, and we have only just got started. But so far, thousands of exoplanets have been detected and at the time of writing, there are 5 which appear to be similar to Earth in their conditions to support life.
Assuming we believe that life exists elsewhere in the universe, what are we doing to make contact? Since the 1990s, SETI has been searching for signals which may indicate an advanced lifeform who are capable of sending out radio signals of different wavelengths. SETI stands for Search for Extraterrestrial Life and has radio telescopes at various locations continually listening out for that first signal. So far, it has been quiet.
However, we are also sending signals out into the galaxy. One of two deep space probes, the Voyager series, carries information about the human race and our place in the galaxy. Some people think this is stupid in case they do not come in peace. Voyager also contains a Golden Record which contains greetings in 55 languages, sounds and pictures of us and our planet. It is also important to note that since radio and TV broadcasts have been invented, those radio waves and TV signals have all escaped into space and might one day be picked up by an alien civilisation. If they start watching some of our reality TV, they might give us a wide berth!
John Pullen 