Friday, June 27, 2008
More than one Earth
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 in a statement. The trio of planets orbit a star slightly less massive than our Sun, 42 light years away towards the southern constellations Doradus and Pictor.
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. And they circle their star on faster, closer orbits than Earth, which takes 365 days to orbit the Sun – one whizzes around in just 4 days, one takes 10 days and the slowest takes 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.
Nearly 300 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 by studying the way an orbiting planet makes its host star wobble very slightly.
"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. Read an exclusive story about the recent advances in extrasolar planet hunts. 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 as massive as 22 Earths, orbiting every four days, and a Saturn-like planet with a 3-year period. "Clearly these planets are only the tip of the iceberg," said 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."
Since light travels faster than sound, people appear brighter before you hear them speak.