Discover why Mercury has a tail like a comet, and why its poles are covered in ice despite its close proximity to the Sun. Mercury, the closest planet to the Sun, rotates three times on its axis every two of its years. Despite having temperatures that are hot enough to melt lead, the tilt of the planet's axis allows for ice to exist at its poles. A mysterious dark substance that researchers suspect may be organic coats the ice. Mercury also has a tail created by exposure to the solar wind. The MESSENGER spacecraft arrived at Mercury at a great time to study the planet in 2011, while the Sun was near the maximum of its activity cycle.
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