Wordnet 3.0
NOUN (1)
1.
the magnetic field of a planet;
the volume around the planet in which charged particles are subject more to the planet's magnetic field than to the solar magnetic field;
The Collaborative International Dictionary of English v.0.48:
magnetosphere \mag*net"o*sphere\, n.
the magnetic field of a planet; the volume around the planet
in which charged particles are subject more to the planet's
magnetic field than to the solar magnetic field.
[WordNet 1.6]
WordNet (r) 3.0 (2006):
magnetosphere
n 1: the magnetic field of a planet; the volume around the
planet in which charged particles are subject more to the
planet's magnetic field than to the solar magnetic field