There Were Many Books In The Series

And I loved them all.

A mystery man inspires two boys to build a space ship which takes them to the planet of Basidium to help the Mushroom people. When two boys find a mysterious ad in a newspaper asking for two young boys to build a spaceship, they quickly construct one out of old tin and scrap wood, and bring it to the advertiser. This man is the mysterious Mr. Bass, a scientist living in an observatory who goes unnoticed by most of the townspeople for some reason. He shows the boys a previously undetected satellite of the earth, the eponymous planet, that can only be seen with a special filter he has concocted. He gives them some special fuel he invented to power their spaceship, and tells them to fly to the mushroom planet (after getting their parents' permission). He warns them that their trip will only be successful if they bring a mascot.

When it is time for launch, they grab a hen at the last moment for a mascot, and rocket into space. They wake up on the mushroom planet, a small, verdant world covered in soft moss and tree size mushrooms. They quickly meet some residents of the mushroom planet, small men with large heads and slightly green skin, the cousins of the mysterious Mr. Bass. They tell the boys that their planet has had a crisis and everyone is slowly dying. The boys meet up with the king of the planet, the Great Ta, and end up solving the natives' problem, before returning to Earth.

The mushroom people's crisis was a lack of sulfur. They resolved this with their mascot hen, as chicken eggs have a high sulfur content.

Yes, that's right, ONE CHICKEN layed enough eggs to save an entire planet. Why this isn't already a summer blockbuster confuses me. You got everything you need for a kick-ass franchise with an automatic KFC product tie-in opportunity. The money just prints itself.