Distant Planets Found to Pollute Their Suns

Astronomers have recently analyzed the chemical composition of distant stars and discovered intriguing evidence of pollution on their surface, caused by the planets orbiting them. It seems that dwarf stars display iron enrichment on their surface, most likely caused by planetary debris thrown in space and falling onto them.

"It is a little bit like a Tiramisu or a Capuccino," says Luca Pasquini from ESO, lead-author of the paper reporting the results. "There is cocoa powder only on the top!'

The interesting thing is that only dwarf stars have been reported to suffer from this pollution phenomenon, although planetary iron debris is also likely to fall on red giant stars. The most probable explanation is that the red giants continuously "stir" their composition, mixing the elements, so that no detectable layer of iron can form on the surface.

Also, the study discovered that stars that have planets around them are on average almost twice as rich in metals like iron than their counterparts with no planetary system. This answers the question raised when exoplanets were first discovered around iron-rich stars: does this richness in metals enhance planet formation, or is it in fact caused by the presence of these planets?

When examining the surface of red giant stars, the only thing that can really be studied in terms of chemical composition, they found that the distribution of metals in fourteen of them, which had stars around them, was rather different from normal planet-hosting stars.

"We find that evolved stars are not enriched in metals, even when hosting planets," says Pasquini. "Thus, the anomalies found in planet-hosting stars seem to disappear when they get older and puff up!" The explanation seems to be a dilution produced by these giants, 35 times higher than in dwarf stars, which hides the real concentration of iron.

"Although the interpretation of the data is not straightforward, the simplest explanation is that solar-like stars appear metal-rich because of the pollution of their atmospheres," says co-author Artie Hatzes, Director of the Thüringer Landessternwarte Tautenburg (Germany), where scientists obtained some of the data.