1. The volume of space, surrounding a planet, controlled by the planet's magnetic field, and acting as a magnetic "shell".

The earth's magnetosphere extends 64,000 kilometers or 40,000 miles toward the sun, but many times this distance on the side away from the sun.

2. The magnetic field of a planet in space.

A planet's magnetosphere is molded by the solar wind into a teardrop shape, its point directed away from the sun.