Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies. This is a major achievement because, in relative terms, planets are very small and do not emit light. Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult. The first question to answer is whether a planet can actually support life. In our own solar system, for example, Venus is far too hot and Mars is far too cold to support life. Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.
Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'. Imagine a star up to twenty times larger, brighter and hotter than our own sun. A planet would have to be a very long way from it to be capable of supporting life. On the other hand, if the star were small, the life - supporting planet would have to have a close orbit round it and also provide the perfect conditions for water: not too hot and not too cold, as otherwise water would turn to vapour or ice.
Secondly, we may wonder whether there is life on other planets. At present we can only detect life - forms that are based on carbon. Consequently, a search for non - carbon - based life forms may prove to be a fruitless search. However, it is probably a mistake to assume that other life - forms would be similar to our own. They might not need water or oxygen, or even light, as we do. Instead, they might have developed other ways of growing, moving or reproducing.
Finally, we may ask whether life on other planets would be friendly or hostile to us. The answer to this question depends on whether we consider them as potential friends or foes. If we consider them as friends, we will be more likely to welcome them. If we consider them as foes, we will be more likely to fear them. However, given the vastness of the universe, it is more likely that we will never know the answer to this question.