To address this question with clarity, it seems prudent to ask: Has it been determined with certainty that there is intelligent life on earth? We may hope and most of us assume there is, but it is a bit of a self-aggrandizing definition that some might find highly suspect.
Asking what is possible, including whether there is intelligent life elsewhere in the universe, can be a frustrating exercise because the ultimate answer can only be a statistical probability, not an absolute conclusion. Humanity simply has not existed long enough as a carbon-based, self-aware entity, has not been able to collect nearly enough meaningful or conclusive information, and as yet does not have a definitive way to collect precise enough information to absolutely confirm the hypothetical. With these rather blaring caveats in mind, intelligent life beyond earth is possible and most would say probable.
That it is statistically probable means that it is also fascinating to speculate about that possibility and the forms that life might take. We may not be able to answer the question of extraterrestrial life directly, but humanity can do some extrapolating since proof, at this point, is not within our powers of observation and is way beyond our technological means to determine.
What we do have in considering the possibility is: observation, information, analysis, conclusion and extrapolation.
If, in our extrapolation, we start with what we know, and use earth as a microcosm of the universe, the statistical probability effectively demands that there is “intelligent” life beyond earth. Consider the locations on earth that we thought could not sustain life, yet they do. Man tends to be a tad arrogant in assuming he has the competence to be the sole arbiter of and have the capacity to restrict the definition of life based only on our limited understanding of what life is.
Perhaps the real question is: Can man expansively define intelligent life and once defined, does he have the capacity to recognize extraterrestrial life that does not meet our perceived definition of “intelligent.” This means that other potential forms of life may be considered extremely intelligent for the environment in which they developed, but have little or no relation to what “we” might describe as intelligent.
When it comes to the universe, not limiting ourselves to just the Milky Way Galaxy” but to the infinity of space, we must face the concepts of distance, time and limitless variation. Unfortunately, humanity’s limitations make it impossible to do anything more than speculate and hypothesize which is the fun.
The National Aeronautics and Space Administration released a report calculating there could be as many as two-billion earth-like planets in the Milky Way Galaxy alone. Or as researcher Joseph Catanzarite, an astronomer at NASA's Jet Propulsion Laboratory put it in Space.com, “This means there are a lot of Earth analogs out there - two billion in the Milky Way galaxy."… "With that large a number, there's a good chance life and maybe even intelligent life might exist on some of those planets. And that's just our galaxy alone - there are 50 billion other galaxies." This latest report expands the possibility of life and “intelligent life” exponentially.
It is difficult not to be self-restricting by defining life “as we know it” as the ultimate characterization. Just in the past fifty years, we have discovered life on our own planet in places we regarded as incompatible with life as we define it. Scientists had to redefine the concept of “life sustaining” habitats. Has man also egotistically eliminated the possibility that life exists in places other than just planets. Is it possible that life may exist in space itself. It is a question that forces us to be more circumspect when condescendingly assuming that man’s definition of intelligent life, may be highly restrictive.
With all this said, the best we can conclude is that the possibility of life beyond earth is more than a possibility, it is a probability.