Astronomers raised hopes that humanity might not be alone in the universe by announcing on Thursday they have detected the most promising hints yet of life on a distant planet.

But given the age and vastness of the universe, a different question has long puzzled some scientists: why haven't we already come in contact with aliens?

"Where is everybody?" Enrico Fermi asked fellow famous physicists including Edward Teller over lunch in 1950.

This quandary was named Fermi's Paradox.

"It's a numbers game," Jason Wright, the director of the extraterrestrial intelligence centre at Pennsylvania State University, told AFP.

The Milky Way is around 10 billion years old and is home to more than 100 billion stars.

This suggests there is likely a mind-boggling number of potentially habitable planets in our home galaxy alone.

That could include K2-18b, where astronomers said Thursday they have detected signs of a chemical that is only produced by microbial life on Earth.

Wright said Fermi's Paradox essentially suggests that -- given enough time -- "every alien species will eventually have their own........

© International Business Times