Simplify the following text for a Grade 7 native English-speaking person.
Original: There are several extinct volcanoes on Mars , four of which are vast shield volcanoes far bigger than any on Earth . They include Arsia Mons , Ascraeus Mons , Hecates Tholus , Olympus Mons , and Pavonis Mons .
Simplified: Volcanoes are also found on planets other than Earth , like the Olympus Mons on Mars .