Are there planets beyond the Solar System where life might have got going? Yes, I think so. What we know about life on Earth is that it can spring up, and hold on, in the most unlikely and seemingly inhospitable environments. For example, the 8-foot tube worms that thrive on the hydrogen sulfide pouring from hydrothermal vents up to 8000 feet below sea level, at temperatures over 300 degrees celsius, under enormous pressures. See http://www.seasky.org/deep-sea/hydrothermal-vents.html for more detail. With dozens, hundreds, thousands of exoplanets already located in the habitable zone of their star, despite the extreme difficulties of tracking them down, I think it’s safe to assume that there is some environment out there that can replicate conditions similar to the most unfriendly life-supporting habitats on earth. If there’s one thing you can conclude from studying life on this planet, it’s that it is very, very tenacious.
Similarly, there may be environments even in our own solar system that could support some basic form of life. If so, you can bet it will be very hard to find. It took until the end of the twentieth century to discover the giant tubeworms of the deep sea hydrothermal vents here on Earth. Imagine how much harder it is going to be to explore the deepest nooks and crannies of other moons and planets. Once you start to consider bodies beyond our own solar system, how much harder still. So just because we have not found it, does not mean it can’t be there. The universe could be teeming with life beyond our world and we would not know.
But of course, what really grabs us is the idea that there might be intelligent, organised, perhaps civilised, life out there in the stars. Life capable of reasoning, developing technology and maybe curious about us. We have learned how long it takes for visible light and other forms of electromagnetic radiation to reach us from distant stars and galaxies. The nearest such civilisation – if it exists – could be thousands or more likely millions, or more likely still, billions of light years away from us. We have been making enough commotion to be be noticed for only a hundred years or so with our radio waves and human engineered electromagnetic communication. Nobody is going to know we are here yet. If we find signs of civilised, communicating life around distant stars then it could only be from signals that were older than we have existed as a species. I am not a professional but I imagine that these ghostly hopes and hints are what impelled many career astronomers to to take up their calling.
It seems to me arrogant to think that we are the only intelligent, communicating, technology-developing species in this vast universe. If we are alone, then we had better start taking a lot more responsibility than we have displayed so far. We are the caretakers, not just of this demonstrably fragile planet, but of the universe itself. If we are not alone, then we had better grow up if we are to be accepted into any mature galactic or intergalactic society.