Image: MediaFarm / Niels Bohr Institute
Read aloud Planets form only around stars that have a large proportion of heavy elements? that's only true for gas giants like Jupiter and Saturn. Small planets are relatively undemanding according to recent results of an international research team. They arise around different types of stars, even those that receive very little heavy elements. Signs of the existence of 3, 000 planets in other suns have been discovered by astronomers so far. Researchers led by Lars Buchhave from the University of Copenhagen have now studied the stars of 2, 300 of these exoplanets. The data was based on data from the Kepler Space Telescope. "We wanted to find out if planets are just around certain stars, or if there is a connection between the size of a planet and the type of star it circles around, " says Buchhave.

A new solar system including planets is created by the collapse of a gas cloud. Contains enough elements that are heavier than helium and hydrogen, can form planets. ? Enough heavy elements? So far, that means: At least half of the heavy elements of the sun.

The results of Buchhave's team now suggest that much less is needed for the formation of small planets: Compared to gas giants, the existence of smaller planets is not dependent on a star with a high proportion of heavy elements. Planets up to four times the size of the Earth form different kinds of stars? even those with few heavy elements ?, Buchhave reports of his discovery. A proportion of one quarter of the heavy elements of the sun is therefore sufficient.

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Another surprise brought the large number of stars to circle the small planets. Earth-like planets are probably much more common than expected. And older. For in his childhood years the universe did not contain as many heavy elements as today. Accordingly, no large planets could form, but smaller ones.

This in no way contradicts the generally accepted theory of the formation of planets, say the researchers, but merely specifies them: For the formation of the giant gas giants requires a large amount of heavy elements, so that fast enough? So in about five million years? can form large planetary cores that hold gases in their environment. Significantly smaller amounts of heavy elements are not enough, but to create small planets.

Lars Buchhave (University of Copenhagen) et al .: Nature, doi: 10.1038 / nature11121 © science.de? Marion Martin

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