Stars’ missing elements could signal lurking small planets

Solar chemistry suggests best places to hunt

BEIJING — Rocky planets zipping around distant stars might reveal themselves in the chemical elements missing from their host star.

Compared to stars like it, the sun contains fewer planet-building elements such as aluminum, calcium and silicon, Jorge Melendez of the University of Sao Paolo in Brazil said on August 27 at the International Astronomical Union’s general assembly meeting. “For some reason, the sun is missing these more heavy elements.” So stars like the sun might be a good place to hunt for rocky planets — and Melendez and his colleagues are doing just that.

While astronomers already knew that stars accompanied by giant planets contain more heavy elements, this work suggests that chemistry could also flag the presence of smaller, terrestrial planets.

So far, one candidate shines brighter than the rest: a star called HIP 56948, 200 light-years from Earth, whose light very closely resembles the sun’s chemical signature. While no planets have been found orbiting that star yet, Melendez is still looking.

“That happens to be the star that’s an almost identical copy of the sun,” Melendez said. “In our opinion, it could be a very good target.”

To assess the elemental signatures written into the solar twins, Melendez and his colleagues spied on 11 stars using the Magellan telescope in Chile. The scientists found that the sun is different from most of those stars, and suggest that building rocky planets depletes the amount of planet ingredients available to the forming star.

While the idea is compelling, it needs to be verified, said Nader Haghighipour of the University of Hawaii at Manoa. “It’s an approach that, considering our solar system, seems to be viable,” he says. “Until they find one or two systems with planets, it’s hard to say anything.”

Melendez and his colleagues are currently looking for small planets around roughly 75 solar twins, using the super-sensitive HARPS instrument at the La Silla Observatory in Chile.

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