NASA developed this composite image of Mercury's south side by using the photographs taken during the Mariner 10 mission. Just like our moon, Mercury reflects up to 6 percent of the sunlight it receives. Because it lacks a real atmosphere, Mercury is sort of like a piñata in space. Meteors do not disintegrate before connecting with the planet's surface, so impacts are powerful. But like Earth, Mercury has a mantle crust and an iron core. Experts believe that the craters at the poles of Mercury may contain ice because they are constantly shielded from the sun's rays.