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Exoplanets with exotic rocks

Artistic representation of rock debris being pulled toward a white dwarf

NOIRLab / NSF / AURA / J. da Silva

The rocky planets orbiting stars outside our Solar System may have a very different chemical composition to Earth. This is the conclusion reached by Siyi Xu, an astronomer from the USA’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab), and Keith Putirka, a geologist from California State University, USA, after they analyzed the atmospheric composition of 23 white dwarfs located up to 650 light years from the Sun. A white dwarf is what stars like the Sun become after they explode and expel their outer layers. The atmospheres of these stars contain only hydrogen and helium. The remaining stellar core, however, is so dense that it attracts matter from nearby planets and stars. In the atmospheres of the white dwarfs they studied, Xu and Putirka identified calcium, silicon, and magnesium, and they then calculated which minerals and rocks may have existed on nearby planets based on the concentrations of these elements. The number of different compositions is high, some unseen in our Solar System (Nature Communications, November 2).