"Ice Planet Adventure" by Geronimo Stilton (Geronimo Stilton Spacemice, Book 3)

Geronimo Stilton meets outer space in this cosmically fun spin-off series!

Friends of the spacemice have disappeared on a strange ice planet, Polarix! Geronimo Stiltonix and his crew are called to search for them. When the spacemice arrive on Polarix, they're surprised at the inhabitants -- cute little aliens that look like colorful fuzz balls! But are these creatures as harmless as they look?