Simplify the following text for a Grade 4 native English-speaking person.
Original: Mimas ( , or as Greek Î Î Î 1\/4 á 3\/4 Ï ) is a moon of Saturn which was discovered in 1789 by William Herschel .
Simplified: Mimas ( from the Greek Î Î Î 1\/4 á 3\/4 Ï ) is one of Saturn 's largest moons .