Simplify the following text for a Grade 8 native English-speaking person.
Original: 51 Pegasi b , also called Bellerephon or 51 Peg b , is the first extrasolar planet that was discovered orbiting a main-sequence star .
Simplified: The name 51 Pegasi b is the official astronomical name of the planet . As with all extrasolar planets , the ` b ' is used to indicate that this planet was the first discovered orbiting its parent star .