Astronomers have discovered the three smallest planets yet orbiting a single red dwarf star beyond the sun.

Using data from NASA Kepler mission, the planets were found to be 0.78, 0.73 and 0.57 times the radius of Earth and orbit the KOI-961 star.

All three are rocky like the Earth, and the smallest - named KOI-961.03 - is roughly the size of Mars. The largest has been named KOI-961.01, while the middle-sized is KOI-961.02.

The location of the trio is too hot for them to be in the habitable zone - where liquid water could exist - but out of more than 700 planets confirmed to orbit other stars, only a handful are known to be rocky.

Doug Hudgins, a Kepler program scientist at NASA Headquarters in Washington said: "Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far.

"Finding one as small as Mars is amazing and hints that there may be a bounty of rocky planets all around us."

John Johnson, the principal investigator of the research from NASA's Exoplanet Science Institute at the California Institute of Technology in Pasadena, said: "This is the tiniest solar system found so far.

"It's actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy."

Phil Muirhead, lead author from the new study from Caltech, added: "These types of system could be ubiquitous in the universe. This is a really exciting time for planet hunters."

Earlier this week it was suggested an Earthlike moon, reminiscent of the fictitious Tattoine could exist in a double-star system.