VENUS vs. MARS Venus, the second planet from the sun, is only about 1 and 3/4 the size of Mars, and 71/2 times as heavy. Here are some comparisons: Venus's Radius: 6,052 km, 78% wider than Mars Venus's Mass: 4.87 x 1024 kg, seven and one half times Mars' mass. Venus's Density: 5.24, 33% higher than Mars' density.