Mercury is the closest planet to the sun.
We learned most of what we know about Mercury
in 1974 when the tenth in the Mariner series
flew right by it. NASA hopes to send a spacecraft
back to Mercury, the MErcury Surface Space ENvironment
GEochemistry and Ranging (or MESSENGER) would launch
in 2004, fly by Mercury twice in 2008, and then go
into a year-long orbit of Mercury beginning in 2009.