Mercury is the closest planet to the Sun, but it also has the most eccentric orbit - that's why it takes 87 days to rotate on its axis. Because of this erratic movement, most of Mercury is frozen solid or hot molten rock. The only place where ice has accumulated is in a thin veneer near the surface. However, even though it is the smallest planet out there, it still has great influence on Earth's climate and environment. As it turns out, Mercury has the strongest magnetic field of all the planets except for Earth too!