On Earth the radius of the core is known very exactly from the study of how earthquake waves move through the planet. For Mars, there is no such data. Two seismometers were flown to Mars on the Viking mission, though one failed to deploy on the planet. The other seismometer detected one Mars quake, not enough to learn anything about the Martian interior. The core of Mars, therefore, has to be modeled from theory and remote sensing data. Mars's core is thought to be a mixture of iron and iron sulfide.To match the planet's density and size, a certain amount of iron has to be present in the core. Sulfur makes the core material less dense and thus allows a larger core while still matching the density and size requirements. Because of this uncertainty, the radius of Mars's core cannot be constrained very tightly. It has been estimated to be between about 1,100 and 1,370 miles (1,800 and 2,200 km) by Yingwei Fei at the Carnegie Institute. He made the estimates by using a parameter called the moment of inertia factor of the planet. The moment of inertia of a planet is a
What Is Pressure? The simple definition of pressure (p) is that it is force (F) per area (a):
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