The first spacecraft from Earth to visit Mars was Mariner 4 in 1965. Since then, several robotic spacecraft have flown by, orbited, or landed on Mars and sent back lots of information about this world so different from our own.
Mars is a cold, bleak wasteland, with very thin air that we Earthlings could never breathe. However, many of the pictures our telescopes, orbiters, and rovers have sent back show signs that liquid water might have been on the surface of Mars long ago. Also, we can see ice caps at the north and south poles.
All these signs of water are very exciting. Why? Because on Earth, almost everywhere there is water, there is life. Whether the water is boiling hot or frozen, some sort of creature seems to thrive in it. Is it the same on other planets? If water once flowed on Mars, did life once thrive there too? Or, maybe there is still water on Mars, only it has gone underground. Could there be tiny life forms—like bacteria—on Mars even now?
NASA's Mars Exploration Program is about "Following the Water." Even if we do not find life on Mars, if there is water, perhaps someday Mars could be inhabited by us!
NASA's four goals in exploring Mars:
Image credits (from top left): Image of Martian ice clouds [NASA//Hubble Heritage Team (STScI/AURA)]; Artist's depiction of Mars Global Surveyor [NASA]; Possible Martian fossil [D. McKay (NASA /JSC), K. Thomas-Keprta (Lockheed-Martin), R. Zare (Stanford), NASA]; Martian dust storm [Malin Space Science Systems, MGS, JPL, NASA]; Olympus Mons [NASA/USGS]; Mars explorers poster [NASA/KSC]