Mars is the planet that many expect will be the second extraterrestrial world that humans explore. The surface of Mars is a rock strewn reddish desert covered with craters from meteor impacts and basaltic rock indicating lava flows. There is evidence that water once flowed on its surface, which has lead to longstanding speculation that it may once have had an environment in which life could have arisen.
The George W. Bush Administration has dramatically shifted the priorities of NASA from focusing on the International Space Station and Hubble Space Telescope which were Clinton era priorities to returning with manned missions first to the Moon and then to Mars. Some have questioned whether the massive expenditure of funds involved in such missions is worth it, given other pressing budget considerations such as the second Bush administration's disasterous Iraq War. These are the same observers who object to any government involvement involving space or other non-medical research. More far sighted observers note that compared with the obscene waste of Federal monies for the War in Iraq, a mission to Mars would give hope to many and help to re-open the space frontier for all of humanity.
Mars was named after the Greek god of war, and the word is sometimes used metaphorically to make that reference.