Red Planet

Red Planet came out in 1949, as one of the novels Heinlein wrote for younger readers under the Scribner's imprint. The edition published that year contained a number of changes the publisher had insisted on, and Del Rey brought out a version after his death that restored what he had written.

Humans have settled Mars, but they have no political power: the planet is run by an administrator appointed by a company based on Earth. Jim Marlowe and Frank Sutton are colonial teenagers travelling to the Lowell Academy for the school year, and Jim has brought his pet, a round furry Martian ball named Willis the Bouncer, about the size of a volleyball, roughly as clever as a human child and able to remember and reproduce any sound it hears.

On the way, Willis wanders off and meets one of the adult Martians, a three-legged being that takes the boys and the creature to take part in a ritual it calls growing together with others of its kind. They share water with the Martians and become water friends, and the encounter sits at the centre of the story: the first appearance in Heinlein's fiction of the wise elder race of Mars.