When searching for exoplanets that are similar to Earth, astronomers usually search for the world in orbit around a type of star called the red dwarf on M-dwarfs. These types of stars are somewhat similar to our sun and are common in our galaxy, forming about 70% of the stars here. However, new research shows that rocky exoplanets that orbit around a different type of star, white dwarf, can have an interior that is surprisingly similar to our planet.
White dwarfs are the remnants of a star that once shined which has a very strong gravity. Normally, this gravity means the surface of stars is composed of light elements such as hydrogen and helium, but in some cases, you find polluted "white dwarfs" that have heavier elements such as magnesium, iron, and oxygen in their atmosphere. These elements are introduced into white dwarfs when an exoplanet collides with a star, which gives astronomers evidence about what the planet was like before it was destroyed.
"By observing white dwarfs and the elements in their atmosphere, we observe elements in the body that orbit white dwarfs," Alexandra Doyle, a graduate student in the Department of Earth, Planet and Space Sciences at the University of California, Los Angeles, explained in a statement. "The gravity pull of a large white dwarf destroys the asteroid or fragment of the planet orbiting it, and matter falls into the white dwarf."
Doyle and his colleagues looked at the white dwarfs to see what elements existed on the planet used to orbit them. "If I only see white dwarfs, I would expect to see hydrogen and helium," Doyle said. "But in this data, I also see other materials, such as silicon, magnesium, carbon, and oxygen – materials that add to the white dwarf of the orbiting body."
The surprising finding here is how similar exoplanets are to Earth under their rocky exterior. "How similar are the rocks analyzed by researchers to rocks from Earth and Mars? Very similar, "said Doyle. "They are like Earth and like Mars in terms of their oxidized iron. We find that rocks are rocks everywhere, with geophysics and geochemistry very similar. "
This research was published in the journal Science.