Astronomers have described the discovery of a planet outside our solar system that is potentially habitable, with temperatures similar to those found on Earth, as a big step in the search for "life in the universe."
Scientists at the European Southern Observatory in La Silla, Chile, made the discovery with the Eso 3.6 Telescope.
An artistic illustration released by the European Southern Observatory shows the new planet known as Gliese 581 c orbiting a red dwarf star.
The planet is 120 trillion miles away closely orbits a star known as a "red dwarf" - a much smaller, dimmer and cooler star than our sun.
Two teams of astronomers, one in Europe and one in the United States, have been racing to be the first to find a planet such as this outside the solar system.
"It's a significant step on the way to finding possible life in the universe," said University of Geneva astronomer Michel Mayor, one of 11 European scientists on the team that found the planet. "It's a nice discovery. We still have a lot of questions."
The results of the discovery have not been published but have been submitted to the journal Astronomy and Astrophysics.
Alan Boss, who works at the Carnegie Institution of Washington where a US team of astronomers competed in the hunt for an Earth-like planet, called it "a major milestone in this business."
What they revealed is a planet circling the red dwarf star, Gliese 581. Red dwarfs are low-energy, tiny stars that give off dim red light and last longer than stars like our sun. Until a few years ago, astronomers didn't consider these stars as possible hosts of planets that might sustain life.
The discovery of the new planet, named 581 c, is sure to fuel studies of planets circling similar dim stars. About 80 percent of the stars near Earth are red dwarfs.
The new planet is about five times heavier than Earth. Its discoverers aren't certain if it is rocky like Earth or if its a frozen ice ball with liquid water on the surface. If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball, as Mayor suggests, it would be even bigger.
Based on theory, 581 c should have an atmosphere, but what's in that atmosphere is still a mystery and if it's too thick that could make the planet's surface temperature too hot, Mayor said.
However, the research team believes the average temperature to be somewhere between 32 and 104 degrees and that set off celebrations among astronomers.
Until now, the 220 planets astronomers have found outside our solar system have had the "Goldilocks problem." They've been too hot, too cold or just plain too big and gaseous, like uninhabitable Jupiter.
"This could be very important," said NASA astrobiology expert Chris McKay, who was not part of the discovery team. "It doesn't mean there is life, but it means it's an Earth-like planet in terms of potential habitability."