The discovery could prove the theory of "shadow" creatures which exist in tandem with our own and in hostile environments previously thought uninhabitable.
The "life as we don't know it" could even survive on hostile planets and develop into intelligent creatures such as humans if and when conditions improve.
In a press conference scheduled for tomorrow evening, researchers will unveil the discovery of a microbe that can live in an environment previously thought too poisonous for any life-form to survive.
The bacteria has been found at the bottom of Mono Lake in California's Yosemite National Park which is rich in arsenic – usually poisonous to life.
Somehow the creature uses the arsenic as a way of surviving and this ability raises the prospect that similar life could exist on other planets, which do not have our benevolent atmosphere.
Dr Lewis Dartnell, an astrobiologist at the Centre for Planetary Sciences in London, said: "If these organisms use arsenic in their metabolism, it demonstrates that there are other forms of life to those we knew of.
"They're aliens, but aliens that share the same home as us."
The space agency will announce the full extent of the findings at a press conference titled “astrobiology finding which will impact the search for evidence of extraterrestrial life”.
They believe the creature proves the existence of a second form of life that exists in tandem and before and after intelligent life blooms on planets across the universe.
It follows a growing belief that alien life far from being rare is actually abundant in the universe just in a form that is not recognisable as life.
At the heart of his theory is that life on earth may have come and gone many times during the planet's existence.
These creatures are the remnants of the previous inhabitants.
Scientists have also estimated that life of some kind exists on hundred billion trillion Earth-like planets in space.
However it is usually just bacteria and intelligent life such as us is fleeting and only exists for a fraction of the time.
A study last month said that the universe is teeming with planets capable of supporting alien life.
After studying stars similar to the Sun, astronomers found that almost one in four could have small, rocky planets just like the earth.
Many of these worlds may occupy the "Goldilocks" zone – the region where conditions are neither too hot, nor too cold, for liquid water and possibly life.
Planets outside our own solar system are too far away and too small to see directly with telescopes.
Instead, astronomers study distant stars for tell-tale 'wobbles' – caused when stars are pulled by a planet's gravity.
In the last decade, nearly 500 planets have been discovered outside the solar system this way.
In September astronomers announced the discovery of the most Earth-like planet ever found – a rocky world three times the size of our own world, orbiting a star 20 light years away.
The planet appears to have an atmosphere, a gravity like our own and could have flowing water on its surface.
The discovery came three years after astronomers found a similar, slightly less habitable planet around the same small red star called Gliese 581 in the constellation of Libra.
The planet, named Gliese g, is 118,000,000,000,000 miles away – so far away that light from its start takes 20 years to reach the earth.
The latest news induced feverish debate as to whether scientists were about to announce that they had discovered life on other worlds.
"Did they find ET?", asked one headline in the U S., while another wrote, "Has Nasa found little green men?"
Speculation mounted around the world about the mystery information and buoyed people who already believe in aliens.
One said on U.S. news website MSNBC, "It's still hard for me to understand why people can't accept that aliens exist ... ET is real".
"Fact is, life is everywhere," another wrote. 'I don't need some BS announcement to know it because I have common sense.'
A newspaper in South Korea proclaimed "Nasa to hold news conference on alien life".
The event will be streamed live on the internet tomorrow evening.
There are also conspiracy theorists who believe the government is involved in a cover-up of some kind.
"It is embarrassing how our country makes it all a secret and hides and controls what we know," one American ranted, insisting aliens do exist and the U.S. knows it.
"The government lies to us all the time."
Others were more light-hearted in their predictions.
"Looks like good old Elvis finally ran out of hiding places!," joked a person on a science blog.