Mandelbrot: What is the length of the coast of Britain? Infinite
One in four 'soles' could have planets the size of Earth
" The team selected 166 stars of spectral type G ('yellow' as the Sun) and K ('orange-red' and slightly smaller) within a radius of 80 light years from our planet. Observations with the powerful Keck telescope (Hawaii, USA) for five years to determine the number, mass and orbital distance of the planets orbiting these stars.
The researchers were finding ever-smaller planets, down to the smallest that can be detected at present-the so-called super-Earths ", with a mass three times that of Earth.
"Of every 100 typical solar-type stars, one or two have planets the size of Jupiter, about six have planets the size of Neptune and about 12 have super-Earths with a mass between 3 and 10 Earth masses," Howard explains. "If we extrapolate these results to planets the size of Earth (0.5 Earth masses and 2) our prediction suggests that about 23 planets will be found in 100 stars. "
"This is the first estimate of the fraction of stars that have Earth-sized planets based on actual measurements," says Professor Marcy. Previous studies have estimated the proportion of exoplanets the size of Jupiter and Saturn, but never reached to planets the size of Neptune or super-Earths that would allow extrapolation of results to Earth-sized planets.
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According to Howard, "this means that when NASA developed new techniques over the next decade to detect planets the size of the Earth, it is not necessary to look too far."
As researchers have detected nearby planets, there could also be more Earth-sized planets at farther distances, even within the habitable zone located at about the distance that separates our planet from the Sun's habitable zone is the distance a star where a planet is neither too cold nor too hot, allowing the existence of liquid water.
"The results researchers do not agree with current models of planet formation and migration, "said Marcy. It is thought that after his birth in a protoplanetary disk, the planets follow a spiral inward due to interactions with the gas disk. According to these models comes from a 'wilderness of planets within the solar system.
"Precisely in the area where we found most planets, the models predict we would find not a cactus," said Marcy, "and these results will transform the vision of astronomers about how planets form."
Wade of stars
The astronomers used the 10-meter Keck telescopes to measure the tiny wobble or oscillation of each star. Current techniques to detect planets massive enough to cause an oscillation of 1 meter per second or so.
This implies that only saw massive gaseous planets Jupiter type up to three times the mass of Jupiter (thousand Earth masses) orbiting at a distance of up to 0.25 astronomical units (one AU is about 150 million kilometers, the average distance between Earth and the Sun) from its star, or lower, closer to super-Earth and Neptune-like planets (15 and 30 Earth masses).
Only 22 of these stars have planets detectable (33 planets in total) within this range of masses and orbital distances. After taking into account statistically the fact that some stars were observed more frequently than others, the researchers estimated that approximately 1.6% of solar-type stars in the sample had Jovian-type planets and 12% of they were super-Earths (planets from 3 to 10 Earth masses).
The team concludes that if the trend in increased number of smaller planets, 23% of stars have Earth-like planets.
terrestrial worlds According to these statistics, Howard and Marcy, who is a member of NASA's Kepler mission to study faint stars 156 000 to find planetary transits, "estimated that the telescope will detect between 120 and 260" plausibly terrestrial worlds " orbiting a dwarf star 10 000 G and K type with orbital periods close less than 50 days.
"One of the goals of astronomy is to find the value 'eta-Earth' (ηTierra), the fraction of solar-type stars with potentially habitable planets," explains Howard. "This is a first estimate and the real figure could be one of eight instead of four. But this will not be one in 100, which is excellent news. "
already twelve planets have been detected as possible, but requires additional confirmation, says Marcy. If these planets candidates included in the count, the team detected a total of 45 planets orbiting 32 stars.
References: Andrew W. Howard, Geoffrey W. Marcy, John Asher Johnson, Debra A. Fischer, Jason T. Wright, Howard Isaacson, Jeff A. Valenti-Jay Anderson, Doug NC Lin and Shigeru Ida. "The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters. " Science 330, 29 October 2010. Original Date: October 28, 2010 Original Link
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How do astronomers weigh a star that is billions of miles away and is too large for a bathroom scale? In most cases, can not, although they may achieve a better estimation using computer models of stellar structure. 
solar systems like ours may be common in the Universe. According to a study by researchers at the University of California at Berkeley (USA) almost 25% of solar-type stars could have planets similar in size to Earth. The work is published this week in the journal Science 
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