The Magic School Bus Lost in the Solar System is the fourth book in the original book series.
Arnold's cousin, Janet, joins Ms. Frizzle's class for the class trip to the planetarium. But after arriving to find that planetarium is closed for repairs, the Friz decides to launch the bus into space and steers it around the solar system, visiting the moon, Mercury, Venus, and Mars before an asteroid knocks out one of the taillights.
When Ms. Frizzle leaves the bus to investigate, her tether breaks. She gets left behind in the asteroid belt, and the students visit the outer planets without her.
With Janet's quick thinking and use of supply, the class manages to turn the bus around, reconnect with Ms. Frizzle and return to the classroom, making a chart and mobile based on their discoveries.
- This book is loosely adapted into the episode "Gets Lost in Space".
- In the funding Magic School Bus Book Promo for season 3, this book was absent, replaced by Inside A Beehive as the new book of the year.
- In the republished version, the Bus had ZOOM! as its overhead sign.
- On page 23, Arnold thinks, “I really prefer filmstrips”. In the republished version, he says, "I really prefer video games", due to the fact that video games are being more popular among 2000s and 2010s-born fans.
- This book was released as an eBook on LeapFrog devices.