Professor Scott King of the Virginia Polytechnic Institute and State University based his finding on an examination of computer simulations of the three-dimensional convection occurring within Mercury's mantle, between its inner core and outer crust. He expects data from an October fly-by of the Messenger spacecraft to support his conclusions.

King's results contradict the long-held theory that the steep and scalloped-edged cliffs of Mercury resulted from the planet's gradual shrinking and cooling. King said images from the Mariner 10 spacecraft launched in 1973 revealed the cliffs were among the youngest features of Mercury's surface.

That relatively young age is inconsistent with the theory that they formed from a slow process of cooling and shrinkage, King said.

"The timing and orientation of these features are controlled by convection and not global contraction," King said. "Because the model suggests that mantle convection is still active today, gravity and topography data from the Messenger mission may be able to confirm the model."

The study is to appear in the journal Nature Geoscience.