The planets outside the Solar System could have a geological and mineralogical composition more varied than expected and very different from that of the Earth: this is demonstrated by the analysis of the chemical traces they left in the atmosphere of their parent stars after being devoured by them.
The study, published in Nature Communications by researchers at California State University and the Gemini Observatory in Hawaii, suggests that some exoplanets may have unique accretion and differentiation mechanisms, with no equivalent in our solar system.
Researchers Keith Putirka and Siyi Xu discovered this by analyzing the atmosphere of 23 white dwarfs near the Solar System and with the atmosphere 'contaminated' by exoplanet debris. The white dwarfs, in fact, represent the last stage of the evolution of stars such as the Sun which, once the 'fuel' is finished, are transformed: first they become a red giant, then they shrink becoming white dwarfs. In this process they can incorporate some exoplanets that orbit nearby, preserving fragments of their rocky material. By analyzing the atmosphere of white dwarfs, US researchers found low levels of silicon and high amounts of magnesium and iron, which could reflect the composition of the mantle of exoplanets once orbiting these stars. From the comparison with the solar system,no analogies have been found with the rocks typical of the continental crust that abound on Earth.