4 — Mars the Fourth Planet

4 - Mars, Planet #4. Mars is often referred to as the “Red Planet” because of the reddish iron oxide on its surface. Mars is home to the highest mountain in our solar system, Olympus Mons is roughly 3 times as tall as Mount Everest. 4 successful robotically operated rovers have been dispatched to Mars to search for evidence of ancient life including water and organic carbon.