Simplify the following text for a Grade 10 native English-speaking person.
Original: He discovered or co-discovered several comets , including 23P\/Brorsen-Metcalf and 97P\/Metcalf-Brewington ; he also discovered a number of asteroids .
Simplified: He found or co-found many comets , such as 23P\/Brorsen-Metcalf and 97P\/Metcalf-Brewington ; he also found many asteroids .