For a long time it was thought that Mars had no magnetosphere.
NASA sent a spacecraft to Mars. Its name is the Mars Surveyor. It arrived on September 11, 1997. Four days after it arrived, the Surveyor made a discovery.
An instrument on the Surveyor found out that Mars has a magnetic field. This means that Mars acts like it has a huge magnet in the middle of it.
The Earth has a magnetic field too. It is a lot stronger than Mars' magnetic field.