If this question pertains to the planets in orbit of the Sun other than Earth, the answer to it has to be no.
Mercury has no atmosphere, is too cold on one side and too hot on the other. Venus is way too hot and too chemically caustic for life. Mars, could possibly have supported life at some time in the past, but all the available evidence suggests that there is no form of life on mars today. Jupiter’s atmosphere and immense gravity suggests that life would not be possible there. Saturn is way to cold, as are Neptune, and Uranus, and Pluto would be in the same category if it were even considered to be a planet anymore. The one place in our solar system that has been suggested to be a good candidate for life is Jupiter’s moon Europa, but this question specifically states planets so moons don’t count.
Having written off the planets within our solar system, the possibility that life exists on some other planet(s) around other stars looms large, but if we are talking about intelligent life commensurate to human intelligence, the possibilities begin to dim. The Drake equation predicted that intelligent life in our own galaxy should be so regular that all we should have to do is point a high gain high frequency radio antenna at other stars and sooner or later we would pick up a radio transmission from some distant alien culture. After almost 50 years of listening, we have yet to pick up our first signal. Life is apparently rarer than we thought, at least any intelligent variety of it.
There is nothing special about the chemical process that has made life possible here on Earth. It’s all a matter of a predictable chemical evolution that has taken place on the planet. Even so, just the right conditions and a whole lot of time, about a quarter of the total life of the universe was necessary for life to achieve it’s current status on this small blue planet. The National Science Foundation has estimated that there are from 5 to a 100 million species of life on Earth today, just a drop in the bucket compared to all the billions which have come and gone before. And yet, of all these species of life, there has only been one, modern humans, which has evolved a cognitive capacity to even contemplate the possibility of life beyond earth. If the chances that intelligent life will evolve in only one in a billion species, this would suggest that intelligent life at least, is a very rare phenomenon.
Now consider that our solar system just happens to be located in one of the most tranquil neighborhoods of the Milky Way galaxy. The idea that intelligent life would have time to evolve successfully in other more active quadrants of the galaxy, is iffy at best. Beyond the Earths protective and nurturing biosphere, the environment becomes very hostile. But considering that there are more galaxies in the universe than stars in the Milky way, chances are that out there somewhere there is some pseudo being sitting at a computer and writing an article contemplating the possibilities of life beyond its own backyard in the cosmos. The idea that we humans are the only creatures to evolved an awareness of ourselves and the universe we find ourselves in, seems to be just too absurd a notion to entertain. But still, we can not say with any certainty that it is not so….
