The discovery was made by Michel Mayor and colleagues from Switzerland's Geneva Observatory, who used the High Accuracy Radial Velocity Planet Searcher, a telescope at La Silla observatory in Chile, to find the planets.
According to a report in The Australian, the trio of planets orbit a star slightly smaller than our sun, 42 light-years away towards the southern Doradus and Pictor constellations. The planets are bigger than earth -- one is 4.2 times the mass, one is 6.7 times and the third is 9.4 times. They orbit their star at extremely rapid speeds -- one whizzing around in just four days, compared with Earth's 365 days, one taking 10 days and the slowest taking 20 days.
Till date, more than 270 so-called 'exoplanets' have been found. Most are giants, resembling Jupiter or Saturn. Smaller planets closer to the size of earth are far more difficult to spot. None of these planets can be imaged directly at such distances, but can be spotted indirectly using radio waves or, in the case of HARPS, spectrographic measurements. As a planet orbits, it makes the star wobble very slightly and this can be measured.
"With the advent of much more precise instruments such as the HARPS spectrograph, we can now discover smaller planets, with masses between 2 and 10 times the earth's mass," said Stephane Udry, who also worked on the study.
The team also said they found a planet 7.5 times the mass of earth orbiting the star HD 181433 in 9.5 days. This star also has a Jupiter-like planet that orbits every three years. Another solar system has a planet 22 times the mass of earth, orbiting every four days, and a Saturn-like planet with a three-year period.
"Clearly these planets are only the tip of the iceberg, the analysis of all the stars studied with HARPS shows that about one third of all solar-like stars have either super-Earth or Neptune-like planets with orbital periods shorter than 50 days," Mayor said.