Chances of aliens existing have increased significantly after astronomers found two Earth-like planets in neighbouring star systems.
The planets, orbiting a star called Trappist-1, 40 light years away, were first thought to be gaseous.
But thanks to the help of Nasa's Hubble Space Telescope, astronomers have shown that the worlds, which are both about the size of Earth, are primarily rocky and situated in the "habitable zone" around their sun, where mild temperatures make liquid surface water possible.
The discovery of the Earth-like planets shortens the odds on other worlds in our universe hosting alien life.
They were uncovered by Trappist (Transiting Planets and Planetisimals Small Telescope); a new kind of ground telescope in Chile designed to capture infrared light.
Scientists were able to take a more detailed look at the two planets when they passed in front of their parent star at almost the same time.
This "double transit" allowed astronomers to use the Hubble telescope to measure tiny light fluctuations as each planet caused the star's "sunshine" to dip.
This narrow range of dipping starlight wavelengths showed that both planets had compact rocky planet atmospheres. US lead scientist Dr Julien de Wit, from the Massachusetts Institute of Technology's Department of Earth, Atmospheric and Planetary Sciences, noted that if the wavelengths had varied significantly it would have signalled the presence of a large, puffy atmosphere similar to the one that blankets Jupiter.
"The data turned out to be pristine, absolutely perfect, and the observations were the best that we could have expected. The Force was certainly with us," she said.
"We can say that these planets are rocky. Now the question is, what kind of atmosphere do they have? The plausible scenarios include something like Venus, where the atmosphere is dominated by carbon dioxide, or an Earth-like atmosphere with heavy clouds, or even something like Mars with a depleted atmosphere. "The next step is to try to disentangle all these possible scenarios that exist for these terrestrial planets.
To increase chances of new planet discoveries, there are four larger versions of the Trappist telescope being built in Chile, focusing on other ultracool dwarf stars in the southern sky.
"With more observations using Hubble, and further down the road with James Webb (a new space telescope), we can know not only what kind of atmosphere planets like Trappist-1 have, but also what is within these atmospheres," added de Wit. "And that's very exciting."