Regardless of mass, these ‘super earths’ store most of their water in the mantle and would have both oceans and exposed continents – enabling a stable climate such as earth’s, claimed researchers.
“Our 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,” said Nicolas B. Cowan, a post-doctoral fellow at Northwestern University’s Centre for Interdisciplinary Exploration and Research in Astrophysics (CIERA) in Chicago.
In their model, researchers treated the intriguing exoplanets 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.
“Water is constantly traded back and forth between the ocean and the rocky mantle because of plate tectonics. The division of water between ocean and mantle is controlled by seafloor pressure, which is proportional to gravity,” said Dorian Abbot, assistant professor in geophysical sciences at University of Chicago.
“We can put 80 times more water on a super earth and still have its surface look like earth. These massive planets have enormous seafloor pressure and this force pushes water into the mantle,” Cowan told the gathering at the meeting of the American Astronomical Society (AAS) in Washington, DC.
“It doesn’t take that much water to tip a planet into being a waterworld. If earth was 1 percent water by mass, we’d all drown, regardless of the deep water cycle,” he said.
“Whether or not you have a deep water cycle really matters for planets that are one one-thousandth or one ten-thousandth water,” confirmed Abbot.
The ability of super earths to maintain exposed continents is important for planetary climate. On planets with exposed continents, like earth, the deep carbon cycle is mediated by surface temperatures, which produces a stabilising feedback (a thermostat on geological timescales), the researchers added.