Found: Batch of 'super-Earths'
2008-06-16 12:44
Washington - European researchers said
on Monday 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," Mayor said.
The trio of planets orbit a star slightly less massive 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.
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 two 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 Mayor.