PLUTO vs. MARS Pluto is the farthest planet from the sun, and much smaller than Mars. Mars is 3 times as wide as Pluto, and about 5 times as heavy. Here are some comparisons: Pluto's Radius: 1,137 km, 33% as wide as Mars Pluto's Mass: 1.27 x 1022 kg, 2% as massive as Mars. Pluto's Density: 2.06, half as dense as Mars.