HistoryFor a long time it was thought that Mars, like Venus, had no magnetosphere. The Russians first made measurements which suggested that there was a magnetic field present.
Scientists confirmed the existence of a magnetic field surrounding Mars using the magnetometer aboard the Mars Surveyor probe. The magnetic field was found on September 15, 1997, just 4 days after Surveyor plunged into Martian orbit.
Mars Global Surveyor's magnetometer discovered the outermost boundary of the Martian magnetic field -- known as the bow shock. The polarity of the magnetic field seems to be similar to that of Earth, though the field strength is only 1/800 the strength of the Earth's magnetic field.
All previous Martian missions had left inconclusive evidence regarding the presence of a magnetic field. Now we can be sure that Mars has a magnetosphere!