From the category archives:

Wollheim, Donald Allen

When it is discovered that a series of alien installations is destabilizing the sun, the experimental spaceship Magellan is called on to disable them before the sun goes nova. On an incredible voyage of exploration, the Magellan and her intrepid crew travels from one end of the solar system to the other, facing new dangers with every landing. But to stop the aliens from implementing their plans for destruction, they must venture out to the planet Pluto and discover The Secret of the Ninth Planet!