In a recent Astrophysical Journal Letter Jade C. Carter-Bond of the Planetary Science Institute in Tucson, Arizona, and co-investigators, report that computer simulations of terrestrial planet formation show that, chemically, they can be anything but Earth-like.
Other stars have proportionally different abundances of elements. And, observations of white dwarfs show that they are polluted with a wide chemical range of debris from gravitationally torn apart planets.
The team's simulations produce a variety of planetary compositions, depending in part where the planet forms inside the dusty element-rich disk encircling a newborn star.
The scientists say that there are two key chemical ratios that determine the composition of terrestrial planets. And this could have far reaching implications for habitability, they caution.
One is the ratio of carbon to oxygen. Earth, Mars, and Venus all have more oxygen than carbon. But there could be "carbon planets" where the ratio tips in favor of more carbon. These planets would have bone dry surfaces where carbides would chemically break apart water to create carbon monoxide and methane rain. Living on such a planet would be like living in Los Angeles, with nothing but smog and asphalt.