Our planet’s hot, gooey center may be the result of a collision between a young Earth and a Mercury-like protoplanet billions of years ago, a study published Wednesday in Nature suggests.

This is “an intriguing conclusion,” Richard Carlson of the Carnegie Institution of Washington writes in an accompanying commentary. Before this study, he writes, “there was only limited (and controversial) experimental evidence” to support such ideas.

Geologists can’t observe Earth’s core directly, but they know from the way seismic waves travel through the planet that the core is made mostly of molten iron and nickel. Those hot substances power the planet’s magnetic field as well as the phenomenon known as plate tectonics. But why the core remains molten some