Michael Mayor -Switzerland's Geneva Observatory
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.
Since the discovery In 1995 of 51 Peg b, the first planet found orbiting a star other than the Sun, researchers have found 270 of these so-called exoplanets, with about half the discoveries done using and an instrument called the Higher Accuracy Radial Velocity Planet Searcher (HARPS), installed on a 3.6-metre telescope at the European Southern Observatory (ESO) at La Silla in Chile.
This new instrument is optimized to detect planets in orbit around other stars ("exoplanets") by means of accurate (radial) velocity measurements with a precision of 1 meter per second. This high sensitivity makes it possible to detect variations in the motion of a star caused by the gravitational pull of one or more orbiting planets, even relatively small ones.
Current technical limitations however have so far prevented the discovery of exoplanets around solar-type stars, if the exoplanets that are less massive than Saturn, the second-largest planet in the solar system. HARPS will break through this barrier and will carry this fundamental exploration towards detection of exoplanets with masses like Uranus and Neptune. Detecting planets much smaller than Neptune requires such precision because the velocity shifts due to the planet are masked by noise in the velocity shifts from the star itself. A further limitation of the radial velocity method is that it doesn't allow astronomers to determine the inclination of the planetary orbit relative to Earth. As a result, only lower limits can be set for the masses of planets found using this technique.
In the case of low-mass stars - like Proxima Centauri - HARPS will have the unique capability to detect big "telluric" planets with only a few times the mass of the Earth.
These newest exo-planet findings, presented at a conference in France, suggest that Earth-like planets may be very common.
"Does every single star harbor 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 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. Continued...
"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 3-year period.
"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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