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one of three stars might have planets
astronomers is a breakthrough in the search for extrasolar planets have succeeded when they discovered three super-Earths - planets with less than ten times the mass of Earth - in orbit around a Sun-like star HD 40307th According to scientists, the evidence suggests that even a Sun-like stars could have three planets.
Since the discovery of planets around a foreign star in 1995, astronomers have made more than 270 exoplanets identified. Most of them revolve around sun-like stars, however, are gas giants like Jupiter or Saturn. According to current statistics about the orbits of 14 stars from such a planet. So-called super-Earths, Planets with masses less than Uranus and Neptune, roughly 15 times Earth's mass which have, however, been found so far are rather rare. Their detection failed, due to the still inadequate technical capabilities.
"Housed perhaps even planets each star? And if so, how many? "Planet hunter Michel Mayor from Geneva Observatory asks. "Once we know the answers, but we are making great progress." For now, astronomers with new instruments to further and more specific look out into space. "With developments such as the HARPS spectrograph on the 3.6 meter telescope at the European Southern Observatory in La Silla, we can now even smaller planets the order of between two and ten times the mass of the Earth discovered, "said his colleague Stephane Udry.
three planets in one go
Using HARPS, the astronomers discovered a system of three super-Earths around a normal Sun-like star. HD 40 307 has a slightly smaller mass than our sun and located 42 light-years away in the southern sky visible between the constellations Doradus and Pictor. "We have made very precise measurements of the velocity of the star over the last five years," said Mayor. "They clearly reveal the presence of three planets."
The fluctuations that the cause planet by gravity in the speed of the central star, are tiny, just a few meters per second. No wonder, their mass but a hundred thousand times smaller than that of its star. Only because of the extreme sensitivity of HARPS instrument could these changes be detected at all.
The values can even close the astronomers on the sizes and rotational speeds of the three planets. The innermost is 4.2 Earth masses and orbits the parent star in just 4.3 days, and the second weighs 6.67 Earth masses and takes 9.6 days to orbit and the third, outermost, 9.4 times the mass of Earth and has to have a orbital period of 20.4 days.
tip of the iceberg
"It seems clear that these planets are only the tip of the iceberg," said Mayor. "The analysis of all the stars we have investigated so far with HARPS shows that have about one-third of all solar-like stars either super-Earth or Neptune-like planets with orbital periods shorter than 50 days." Since planets more easily in a tight, short orbit discover, as such, on wide, outer orbit, it is mainly this type that have dominated the discoveries. But researchers sic h are sure that the space still a lot further, even Earth-sized planets waiting to be discovered.
It is highly likely that there are many other planets: not only super-Earth and Neptune-like with longer periods, but also Earth-like we have not yet been able to discover, "Sun Udry. "If then the known Jupiter-like planet one of these, then you get very quickly to the conclusion that planets are quite common."
(NPO, ESO, 17.06.2008)
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