Simplify the following text for a Grade 8 native English-speaking person.
Original: 16 Psyche is a very big Main belt asteroid , well over 200 kilometers in diameter , and likely the biggest of the metallic M-type asteroids .
Simplified: 16 Psyche ( , or as in ) is one of the ten most massive main-belt asteroids . It is over 200 kilometers in diameter and contains a little less than 1 % of the mass of the entire main asteroid belt .