For 40 years, following its discovery in 1971, it was the tallest mountain known in the Solar System. However, in 2011, the central peak of the crater Rheasilvia on the asteroid and protoplanet Vesta was found to be of comparable height. Due to limitations in the accuracy of the measurements and the lack of a precise definition of "base", it is difficult to determine which of these is taller.[n 1]