Chances of alien life existing beyond the Earth have been boosted by the discovery that the number of stars in the universe might be triple current estimates.
Astronomers have learned that small, dim stars known as red dwarfs are far more prolific than was previously thought.
Using powerful instruments at the Keck Observatory in Hawaii, they detected faint light from red dwarfs in eight massive "elliptical galaxies" between 50 million and 300 million light years away.
Their findings show about 20 times more of the stars in the galaxies than in our own Milky Way.
As a result, it may be necessary to revise the total number of stars in the universe upwards by a factor of three.
There are already estimated to be 10 to the power of 21 - or 10,000,000,000,000,000,000,000 - stars in the expanding observable universe, or that portion of the cosmos it is possible for us to see given the speed of light.
The discovery is published in the journal Nature.
Dr Pieter van Dokkum, one of the astronomers from Yale University in Connecticut, US, said: "No-one knew how many of these stars there were. Different theoretical models predicted a wide range of possibilities, so this answers a long-standing question about just how abundant these stars are."
Boosting the number of red dwarfs also raised the number of planets orbiting the stars - and the odds in favour of extraterrestrial life, he added.
The red dwarfs discovered were typically more than 10 billion years old, which provides enough time for complex life to evolve.