Massive terrestrial planets, called "super-Earths," are known to be common in our galaxy, the Milky Way. Now a Northwestern University astrophysicist and a University of Chicago geophysicist report the odds of these planets having an Earth-like climate are much greater than previously thought.
Nicolas B. Cowan and Dorian Abbot’s new model challenges the conventional wisdom which says super-Earths actually would be very unlike Earth — each would be a waterworld, with its surface completely covered in water. They conclude that most tectonically active super-Earths — regardless of mass — store most of their water in the mantle and will have both oceans and exposed continents, enabling a stable climate such as Earth’s.
Cowan is a postdoctoral fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), and Abbot is an assistant professor in geophysical sciences at the University of Chicago.
"Are the surfaces of super-Earths totally dry or covered in water?" Cowan said. "We tackled this question by applying known geophysics to astronomy.
"Super-Earths are expected to have deep oceans that will overflow their basins and inundate the entire surface, but we show this logic to be flawed," he said. "Terrestrial planets have significant amounts of water in their interior. Super-Earths are likely to have shallow oceans to go along with their shallow ocean basins."
In their model, Cowan and Abbot treated the intriguing exoplanets (planets outside our solar system) like Earth, which has quite a bit of water in its mantle, the rocky part that makes up most of the volume and mass of the planet. The rock of the mantle contains tiny amounts of water, which quickly add up because the mantle is so large. And a deep water cycle moves water between oceans and the mantle.
Cowan presented the findings at a press conference, "Windows on Other Worlds," held January 7 at the 223rd meeting of the American Astronomical Society (AAS) in Washington, D.C.