Earth-like planets may be common

WASHINGTON — European researchers said on Monday that they have discovered a batch of three "super-Earths" orbiting a nearby star, and two other solar systems with small planets as well.

They said their findings, presented at a conference in France, suggest that Earth-like planets may be very common.

"Does every single star harbour planets and, if yes, how many?" asked Michel Mayor of Switzerland's Geneva Observatory. "We may not yet know the answer but we are making huge progress toward it," Dr. Mayor said in a statement.

The trio of planets orbit a star slightly less massive than our Sun, 42 light-years away toward the southern Doradus and Pictor constellations. A light-year is the distance light can travel in one year at a speed of 300,000 kilometres a second – about 9.5 trillion kilometres.

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 four days, compared with Earth's 365 days, one taking 10 days and the slowest taking 20 days.

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 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.

"Clearly these planets are only the tip of the iceberg," Dr. Mayor said. "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."