How alien can alien worlds be?

TL;DR

This study estimates the chemical compositions of potential rocky exoplanets orbiting seven habitable-zone stars, revealing significant compositional differences from Earth and highlighting the need for more detailed analyses.

Contribution

It introduces a method to estimate exoplanet building block compositions based on stellar abundances for selected habitable-zone stars.

Findings

Potential exoplanets may have diverse compositions.

Significant differences from Earth's composition are possible.

Highlights the need for detailed planetary characterization.

Abstract

In an attempt to select stars that can host planets with characteristics similar to our own, we selected seven solar-type stars known to host planets in the habitable zone and for which spectroscopic stellar parameters are available. For these stars we estimated 'empirical' abundances of O, C, Mg and Si, which in turn we used to derive the iron and water mass fraction of the planet building blocks with the use of the model presented in Santos et al. (2015). Our results show that if rocky planets orbit these stars they might have significantly different compositions between themselves and different from that of our Earth. However, for a meaningful comparison between the compositional properties of exoplanets in the habitable zone and our own planet, a far more sophisticated analysis (e.g. Dorn et al., 2017) of a large number of systems with precise mass and radius of planets, and accurate chemical abundances of the host stars. The work presented here is merely the first humble step in this direction.