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RESEARCHERS today said they 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 towards it," Mr Mayor said in a tatement.
The
trio of planets orbit a star slightly less massive than our Sun, 42
light-years away towards the southern Doradus and Pictor constellations.
A light-year is the distance light can travel in one year at a speed of 300,000km per second - or 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
just four days, compared with Earth's 365 days, one taking 10 days and
the slowest taking 20 days.
Mayor and colleagues used the High
Accuracy Radial velocity Planet Searcher or HARPS, a telescope at La
Silla observatory in Chile, to find the planets.
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.
"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," said Mr Mayor.
"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."
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