Mars - magnetic field

Unlike Earth, Mars does not have inner dynamo to keep a proper magnetic field. This does not mean that Mars does not have any magnetosphere. The process is just slightly different from what we know about Earth, or I have written about Jupiter so far for example, in article Magnetosphere of Jupiter.

 First I would like to mention few interesting summaries about Mars:

• Dozens of spacecraft, including orbiters, landers, and rovers, have been sent to Mars by the Soviet Union, US, Europe, and Japan
• 2/3 of all missions failed, see example in article Soviet Mars Probe Program
• First indication of the weakness of the magnetic field: Mariner 4 flyby in 1965 (at closest approach 3.9 radii of Mars) 
• No indication of Earth like dipole
• Phobos-2 observations of solar wind – Mars interaction in 1989 (Solar Wind)

Magnetosphere of Mars is much more simple and smaller than the Earth's magnetosphere. Generally it is formed by the solar wind magnetic field. As magnetic field lines cannot pass through electrically conductive objects, such as Mars, they drape themselves around the planet creating a magnetic cavity, or otherwise a magnetosphere even the planet doesn't have global magnetic field itself. This type of magnetosphere is called induced magnetosphere.  

The first boundary is bow shock, similar to what you would find in front of the boat in the water. There is a huge discussion whether Mars has an ionosphere or not, or how to call it. For sure it has different form than in case of Earth's ionosphere. Mars 4, in article Soviet Mars Probe Program, observed nightside ionosphere.

Remanent magnetism found by NASA’s Mars Global Surveyor

Mars has no longer an internal dynamo, but there is some evidence that it had an internal dynamo in his past, supported by observation of U.S. mission Mars Global Surveyor (I will write about it later). Measurements showed strong magnetic crustal fields on the surface of Mars. They are creating small magnetospheres on the surface which can be very strong.