There are probably no aliens out there - meaning we are entirely alone in the universe, said an astronomer.
Even though there may many earth like planets, their existing conditions are likely to be too hostile to support life-forms such as extra terrestrials (ET), according to him.
Howard Smith, senior astrophysicist at Harvard University, believes there is very little hope of discovering aliens and, even if we did, it would be almost impossible to make contact.
So far astronomers have discovered a total of 500 planets in distant solar systems - known as extrasolar systems - although they believe billions of others exist, the Daily Mail reported.
But Smith pointed out that many of these planets are either too close to their sun or too far away, meaning their surface temperatures are too extreme to support life.
Others have unusual orbits which cause vast temperature variations, making it impossible for water to exist as a liquid - an essential element for life.
Smith said: "We have found that most other planets and solar systems are wildly different from our own. They are very hostile to life as we know it."
"The new information we are getting suggests we could effectively be alone in the universe. There are very few solar systems or planets like ours. It means it is highly unlikely there are any planets with intelligent life close enough for us to make contact."
But his controversial suggestions contradict other leading scientists - who have claimed aliens almost certainly exist.
Only last month Professor Stephen Hawking said the fact that there are billions of galaxies out there made it perfectly rational to assume there were other life-forms in the universe.