Mars's Liquid Center Cooling in Unusual Manner, Study Suggests

During a geophysical survey using a high pressure anvil, which is "capable of producing pressures of up to 6 million pounds per square inch," European scientists determined that Mars' core may be mostly or completely liquid. This is very interesting because Earth's inner core is known to be solid with a liquid metallic convecting core surrounding it. A theory held by the researchers is that solidification of Mars' core may have started already. However, a hypothesis has long been in place, stating that the core of Mars solidified long ago, eliminating its magnetic field. So, the researchers behind this study now feel that Mars' magnetic field may have collapsed when the planet's surface became "one tectonic plate early in its history." Heat from the core would have thereby been muted, stopping the flow of strong liquid currents. This study is important to similar studies conducted on other Mars-sized planets, and can give an example of how a planet's core can be affected when the planet itself is cooling down.

http://news.nationalgeographic.com/news/2007/05/070531-mars-core_2.html