Astrophysicist Neil deGrasse Tyson and host of the show Cosmos believes that intelligent aliens might have visited earth, but they decided not to make contact with the planet thinking there is no intelligent life on earth.

In an interview with MSNBC, Tyson shared that there must be other planets much older than earth that could send out messages. But we did not have the technology to receive their communication. Explaining his statement with an example, Tyson affirmed radio technology is quite common today, but 200 years ago, radio communications' capability was not there on earth.

Tyson also talked about other aspects of the universe like massive amount of organic matter is present in the universe. There are planets older than our Earth and it is quite possible that these planets might have witnessed the rise and fall of intelligent species.

He also shared some scientific mysteries that excite him like the nature of dark energy and dark matter. Tyson shared 85% of the gravity in the universe comes from dark matter that cannot be detected currently.

Inflation theory, also known as the big bang theory, is another concept that excites him a lot. He is unable to understand whether humans are alone in the universe or not. Tyson could also not remain unaffected by the heavy discussions on climate change.

He also discussed the topic on the 'Cosmos' episode that aired on June 2. For the same, he used planet Venus as an example to show what happens when the greenhouse effect level would increase a lot.