EARTH vs. MARS Earth, the third planet from the sun, is Mars' neighbor. It is about 1 and 3/4 the size of Mars, and 7 1/2 times as heavy. It is interesting to note that Mars and Earth have to same total land area. Here are some comparisons: Earth's Radius: 6,378 km, almost twice as wide as Mars. Earth's Mass: 5.97 x 1024 kg, nine times as massive as Mars. Earth's Density: 5.52, 40% more dense than Mars.