Synopsis
Ms. Frizzle's class is learning about the solar system and Arnold's unpleasant cousin Janet, who constantly raves about herself, has joined them. The Friz decides to take the kids on a field trip to the planetarium, but, once they get there, they find the planetarium is closed. However, on the way back to school, Arnold reminds Mrs. Frizzle of the planetarium known as "the big one". Ms. Frizzle pushes a button that makes the bus transform into a rocket and blast off into outer space.
Once in outer space, the bus flies to the Moon, where the kids make the most of the lesser gravity. Ms. Frizzle then takes them to the Sun and then Mercury, Venus and Mars before flying into the asteroid belt. However, while in the belt, the bus is damaged by an asteroid and the Friz flies out to fix the damage with a tether line connecting her to the bus. However, the bus's autopilot malfunctions, causing the bus to fly off, breaking Ms. Frizzle's tether line and leaving her stranded in the asteroid belt.
Janet looks through the Friz's things and finds Ms. Frizzle's lesson book, which documents the information she is supposed to tell the kids during the field trip (complete with "Arnold, are you listening?" written into it.) Janet reads through the book as they pass the outer planets and until they pass Pluto, leaving the solar system. Janet then flips through the book and finds the instructions for the autopilot, so they can fly back to the asteroid belt and rescue Ms. Frizzle.
After they rescue the Friz, they return to Earth. The kids try to tell everyone about their strange trip, but no one believes them.
Read more about this topic: The Magic School Bus Lost In The Solar System