Books like The Mysterious Planet by Lester del Rey

When a planet, moving faster than Earth, entered the Solar System out beyond Pluto, the reporters, for want of a better name, termed it 'Planet X.' 'Planet X, that astronomical curiosity,' became, in a few short weeks, an object of stark terror to the billions of men scattered on the planets around our Sun, from blazing Mercury to frigid Pluto. To Bob Griffith's father, Commander of the Ninth Wing of the Solar Federation's Space Navy, fell the task of investigating the strange visitor whose black ships moved through space without rocket exhaust, and whose weapons literally melted spaceships out of the heavens. As his father's aid, aboard the gleaming LANCE OF DEIMOS that led the reconnaissance fleet, Bob watched in horror the first incident that would start a war which the Solar Federation 'could not win.' This gripping tale that rockets from Neptune's tiny moon of Outpost, base of the Federation's Navy, to the orbit of an Earth threatened with destruction, features a young space cadet and his father, who, while preparing for war, desperately search for peace. How Bob Griffith finds himself a captive on the mysterious planet, Thule; details of life on a world that has learned how to overcome the forces of gravity and momentum; the discussions that rage over the acceptance of a 'wandering planet' into the Solar alliance come alive in a book that vividly creates a troubled era in a fascinating universe of the future!

First publish date: 1953