Short answers, pulled from the story.
Rheasilvia is 505 kilometers in diameter, making it approximately 90 percent as wide as Vesta itself. It covers most of Vesta's southern hemisphere and is one of the largest craters in the Solar System.
Rheasilvia was first identified in Hubble Space Telescope images in 1997. The International Astronomical Union officially approved the name on the 30th of September 2011, following the Dawn spacecraft's arrival at Vesta.
Rheasilvia is named after Rhea Silvia, a figure from Roman mythology described as a vestal virgin and the mother of Romulus and Remus, the legendary founders of Rome.
The floor of Rheasilvia lies about 13 kilometers below the surrounding surface of Vesta. The crater also features a central mound nearly 200 kilometers in diameter at its base, ranked among the tallest mountains known in the Solar System.
HED meteorites are a class of meteorites found on Earth that scientists believe originated from the impact that created Rheasilvia. The collision is estimated to have excavated about one percent of Vesta's volume, scattering debris that eventually reached Earth.
Divalia Fossae is the largest of a series of equatorial troughs on Vesta, approximately 465 kilometers long and 22 kilometers wide. It is thought to be a large-scale fracture in Vesta's crust caused by the same impact that formed Rheasilvia.