Artist’s impression of a baby star still surrounded by a protoplanetary disc in which planets are forming. Using ESO’s very successful HARPS spectrograph, a team of astronomers has found that Sun-like stars which host planets have destroyed their lithium much more efficiently than planet-free stars. This finding does not only shed light on the low levels of this chemical element in the Sun, solving a long-standing mystery, but also provides astronomers with a very efficient way to pick out the stars most likely to host planets. It is not clear what causes the lithium to be destroyed. The general idea is that the planets or the presence of the protoplanetary disc disturb the interior of the star, bringing the lithium deeper down into the star than usual, into regions where the temperature is so hot that it is destroyed. (Credit: ESO/L. Calçada)

ScienceDaily (Nov. 12, 2009) — A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing "lithium mystery" observed in the Sun to the presence of planetary systems. Using ESO’s successful HARPS spectrograph, a team of astronomers has found that sun-like stars that host planets have destroyed their lithium much more efficiently than "planet-free" stars.

"For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins," says Garik Israelian, lead author of a paper appearing this week in the journal Nature. "We have now found that the amount of lithium in Sun-like stars depends on whether or not they have planets."

Low levels of this chemical element have been noticed for decades in the Sun, as compared to other solar-like stars, and astronomers have been unable to explain the anomaly. The discovery of a trend among planet-bearing stars provides a natural explanation to this long-standing mystery. "The explanation of this 60 year-long puzzle is for us rather simple," adds Israelian. "The Sun lacks lithium because it has planets."

This conclusion is based on the analysis of 500 stars, including 70 planet-hosting stars. Most of these stars were monitored for several years with ESO’s High Accuracy Radial Velocity Planet Searcher. This spectrograph, better known as HARPS, is attached to ESO’s 3.6-metre telescope and is the world’s foremost exoplanet hunter. "This is the best possible sample available to date to understand what makes planet-bearing stars unique," says co-author Michel Mayor.

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