Rocky exoplanets could be far more diverse than the worlds in our planetary system
The rocky worlds of our Solar System could be the odd ones out, as a recent study into the remains of long dead planetary systems has found they were very different to our own.
The discovery was made by astronomer Siyi Xu from NOIRLab and geologist Keith Putirka from California State University, who combined their expertise to investigate the geology of planets around other stars. The duo looked at polluted white dwarfs – the remains of once Sun-like stars that have reached the end of their lives, only to have the planets that once orbited them fall into their atmospheres. The remains of these planets then contaminate the atmospheres of the white dwarfs with elements that wouldn’t otherwise be there, but which can be seen in their spectra.
The pair looked at 23 stars using the Keck Observatory to search for geologically important elements – calcium, silicon, magnesium and iron. From this, they were able to piece together what elements, and minerals, the planets were composed of. This showed that most of the planets had a much wider range of rocks than on Earth.
“While some exoplanets that once orbited polluted white dwarfs appear similar to Earth, most have rock types that have no direct counterparts in the Solar System,” says Xu.
The differences were so pronounced the pair had to create new names, such as quartz pyroxenites. The disparity could mean other rocky worlds evolve very differently to any of the four terrestrial planets in our own planetary system.
“Some of the rock types that we see from the white dwarf data would dissolve more water than rocks on Earth, which might impact how oceans are developed,” says Putirka. “Some rock types might melt at lower temperatures and produce a thicker crust than Earth rocks, and some might be weaker, which might facilitate the development of plate tectonics.”
Drawing conclusions about the surface of these planets is hampered by the fact that the minerals that had been observed originated from the planets’ inner regions. As the crust is only a small fraction of the planets’ masses, their signals were overwhelmed by material from the mantel and core. https://keckobservatory.org