Vesta's giant peak

Asteroid Vesta has a central peak inside the enormous Rheasilvia impact basin that rises roughly 19–26 km above the basin floor, according to NASA estimates. That is more than two to nearly three times Everest’s height above sea level. Whether it is unambiguously the tallest mountain in the Solar System depends on definitions and measurements: NASA calls it the second tallest, nearly as high as Olympus Mons on Mars.