JUPITER vs. MARS Jupiter, the fifth planet from the sun, is about 21 times the size of Mars, and almost 3000 times as heavy! Although it is so much more massive, it is not as dense as Mars. Here are some comparisons: Jupiter's Radius: 71,492 km, 21 times as wide as Mars Jupiter's Mass: 1.90 x 1027 kg, 3000 times as massive as Mars. Jupiter's Density: 1.33, 33% as dense as Mars.