Scientists have discovered an Earth-sized planet orbiting the star nearest to the Sun, potentially a major step in the quest to find out if life exists elsewhere in the universe.

The planet, known as Proxima b, is located just four light years away from the Earth, around the red dwarf star Proxima Centauri, a team of European scientists led by British researchers wrote in the journal Nature on Wednesday.

The scientists, who collected data over 16 years, discovered the planet with data from the European Southern Observatory telescope in Chile by monitoring shifts in the light from the star to determine presence of the planet.

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Proxima b has a mass around 1.3 times that of Earth, but orbits much closer to its star, circling it every 11 days.

Given that the star itself is weaker than the Sun, Proxima b could be within the so-called habitable zone, where it is neither too hot nor too cold to support life and where temperatures could allow the presence of liquid water, the researchers said.

Lead author Guillem Anglada-Escude, an astronomer at Queen Mary University of London, described the finding as the "experience of a lifetime.

"It is not unlikely that this planet is quite similar to Earth. The spectacular finding about this, of course, is that this system is so close to our Earth and solar system," said Angsgar Reiners, a German scientist who is among the research's co-authors.

However, it is not clear if the planet has an atmosphere or if it contains water, but "the existence is plausible", he added.