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It might not occur to us surface dwellers very often, but rocks can flow—more like the way exceedingly lethargic toothpaste would rather than water. Exposed to the extreme temperatures and pressures that reign in the hellish realms far below our feet, rocks can practically swim—slowly diving down and bobbing up through much of Earth’s subsurface.

For some rocky worlds around other stars, what is true for Earth’s innards may extend right up to the surface. Super Earths—sometimes rocky exoplanets that are bigger than our pale blue dot but smaller than massive ice giants such as Neptune—have comparatively strong gravitational fields. Thanks to this extreme gravity, some scientists suspect, rocks on such worlds would flow far closer to the surface.

This arrangement would mean rocks that snap, fracture and break might only be found in thin veneers on these exoplanets’ crust. If these rocky super Earths have thick, Venus-like atmospheres or are especially close to their parent star, they might exhibit no familiarly brittle geology at their surface at all. Instead, says Paul Byrne, a planetary scientist at North Carolina State University and lead author of a study on the Super Earths, their surface rocks would be strangely malleable over long timescales, flowing a bit like the stretchy, sugary confections on offer in any earthly candy shop.

Understandably, Byrne has dubbed such worlds “toffee planets.”

The research, presented at the 50th Lunar and Planetary Science Conference in the Woodlands, Tex., has yet to be peer-reviewed. That has not stopped Byrne’steam speculating on what its findings might mean for the myriad super Earths already discovered beyond our solar system. The most striking possibility is that super Earths might not be able to sustain plate tectonics—the drifting of continents and cycling of crustal rock that intimately shapes Earth. Without that process, you can say goodbye to the building of mountains, the creation of oceans and plenty of a planet’s volcanoes, and, just maybe, the evolution of complex life itself.

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Category: Science