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Mitteilung

Exoplanet–Lithium Link Debated

3. August 2010

In a result just published astronomers have used several telescopes, including ESO’s 3.6-metre telescope at La Silla, to measure the properties of 117 Sun-like stars, of which 14 are known to host exoplanets. They measured the amount of the chemical element lithium in the stars, along with other stellar parameters. The researchers have found that the level of lithium in the stars studied decreases with the age of the star, and furthermore that the lithium levels do not behave differently in stars with known planets.

Relatively low levels of lithium are found in our Sun, compared to other Sun-like stars, and there has been much debate about the reason for the difference. One possible explanation is that the presence of planets, as found in our Solar System, may be linked with reduced levels of lithium in the host star. Such a link was indicated in research also done with ESO’s 3.6-metre telescope and its HARPS spectrograph, which was published in 2009 (see eso0942).

The new result indicates a contradiction with the earlier paper, and argues that the Sun’s lithium content is as expected when one takes its age into consideration. This is a good example of the process of scientific research: new results may build on, and in some cases contradict, earlier studies. Scientific research, which takes place at the edge of our knowledge about the Universe, is, by its very nature, a difficult, incremental process.

The research is ongoing with several teams trying to decode the lithium mystery in Sun-like stars. For example, it is thought that the rotation of a star may also affect the level of lithium observed, and that the presence of planets may affect a star’s rotation. Therefore, our understanding of possible links between lithium levels and the age of a star or the presence of planets will develop as more observations are obtained. One thing is certain: we can expect further debate in this exciting field.