Vesta has been suspected as being the source of the HED meteorites since 1970. Dawn's mapping spectrometer verified that proposition. The Dawn team thinks the HEDs came from an impact basin named Rheasilvia, after an ancient Roman vestal virgin priestess. At 310 miles (500 kilometers) in diameter, Rheasilvia is nearly as large as Vesta itself. It most likely formed from a collision that stripped away most of the southern hemisphere's crust, revealing the asteroid's interior.