Mercury is the closest planet to the sun and first of the inner planets which were formed some 4.6 billion years ago. Mercury is a very hostile planet compared to Earth.

Mercury traces an elliptical orbit that ranges from 28 million miles to 43 million miles from the sun, compared with Earth's average distance of about 93 million miles.

During the day temperatures reach 845 deg F. During the night it will dip to a chilly minus 320 deg F. Mercury is made up of iron, which could come in handy if we can find a way to mine it. The hard surface virtually radiates all heat back into space. Mercury is also pockmarked much like the moon and scientists think Mercury is shrinking slightly every year.

The average day lasts 56 Earth days and it takes 88 days to complete a year (go around the Sun). The only spacecraft to explore Mercury close-up was Mariner 10 which executed three flybys of Mercury in 1974 and 1975, surveying approximately 45 percent of its surface.

In August 2004, NASA launched Messenger on a circuitous journey of 4.9 billion miles which will take six years.