Scientists determine the masses of planets by observing the effect of the gravitational field of those planets on nearby objects - mainly upon their moons. By measuring the orbital period and orbital radius of a moon about a planet, Newton's laws of motion can be used to determine the mass of the planet. Phobos, a moon of the planet Mars, was discovered in 1877. It's orbital radius is 9380 km and its orbital period is 0.319 days (2.77 x 104 seconds). Determine the mass of Mars based on this data.