USA: Around 100 million worlds in our galaxy could host alien life, according to a ‘conservative’ prediction by the National Aeronautics and Space Administration.

Scientists believe we are not alone - and predict we’ll know who are nearest neighbours are in 20 years.

Around 100 million worlds in our galaxy could host alien life, according to a ‘conservative’ prediction by Nasa.

The US space agency say we will be able to find that life within the next two decades, with a high chance it will be outside our solar system.

“Sometime in the near future, people will be able to point to a star and say, ‘that star has a planet like Earth’,” said Sara Seager, an American professor of planetary science and physics revealed at a conference in Washington.

“Just imagine the moment when we find potential signatures of life,” agreed Matt Mountain, a space telescope expert.

“Imagine the moment when the world wakes up and the human race realises that its long loneliness in time and space may be over - the possibility we’re no longer alone in the universe.”

NASA astronomer Kevin Hand said: “I think in the next 20 years we will find out we are not alone in the universe.”

Nasa Administrator Charles Bolden added: “I would venture to say that most of my colleagues here say it is improbable that in the limitless vastness of the universe we humans stand alone.”

Mars and a number of moons in our solar system have been the focus of the search for alien life for decades.

But new telescopes launched into space have massively increased the number of planets outside our solar system that may support life.

Since its launch in 2009 the Kepler telescope has found billions of planets in our galaxy.

Kepler also found the first Earth-size planet to orbit in the ‘habitable zone’ of a star, the region where liquid water can exist.

“What we didn’t know five years ago is that perhaps 10 to 20 per cent of stars around us have Earth-size planets in the habitable zone,” said Matt Mountain, director and Webb telescope scientist at the Space Telescope Science Institute in Baltimore.

“It’s within our grasp to pull off a discovery that will change the world forever.”

Nasa is now hoping to launch of the Transiting Exoplanet Surveying Satellite (Tess) in 2017, the James Webb Space Telescope in 2018, and potentially the proposed Wide Field Infrared Survey Telescope - Astrophysics Focused Telescope Assets early in the next decade.

All three missions will be able to track and explore possible sources of alien life in far more detail.