Simplify the following text for a Grade 7 native English-speaking person.
Original: In the late 1970s , following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto 's relatively low mass , its status as a major planet began to be questioned .
Simplified: In the late 1970s , the minor planet 2060 Chiron was found and people learned that Pluto had a small mass. .