At this moment of time, when humanity stands upon the threshold of space and has already launched its first vehicles beyond the atmosphere, there is a centuries-old question which presses more and more urgently for an answer. In almost any astronomy book you will find a chapter devoted to the subject: ” Is there life on other worlds?” – the answer given depending upon the optimism of the author and the period in which he is writing (for there are fashions in astronomy as in everything else).