But We Are Not of Earth — Jean E. Karl

To escape from their dull planet, Meniscus F, Rom Linders, and her friends are determined to become a part of the space program. Known as The Terrible Four at the School/Home for Discoverers' Children, they are anxious to embark on the dangerous and mysterious mission that will take them deep into the galaxy.

Discovering Ariel, the beautiful Earth-like planet, seems like an accident at first, but as time passes they suspect that they have been brought there for a specific purpose. Just how dangerous and terrible is their mission, however, is far worse than anything they could have imagined!