Photograph courtesy NASA
Craters and scarps mark the surface of Mercury, the smallest planet in the solar system (after Pluto's downgrade to a dwarf planet) and the closest to the sun. Mercury's elliptical orbit takes the planet as close as 29 million miles (47 million kilometers) to the stormy star. Mercury speeds around the sun every 88 days, traveling through space at nearly 31 miles per second (50 kilometers per second) faster than any other planet. The length of one Mercury day is equal to 58.646 Earth days.