The European orbiter Mars Express detected ice at the Red Planet's south pole.
NASA's Mars Odyssey, also an orbiter, confirmed water ice at the north pole, along with dry ice -- frozen carbon dioxide -- in 2002. It picked up signs of hydrogen at the south pole, the first indication that water ice might be found there.
Mars Express confirmed Odyssey's suspicions about the south pole. Water is thought to be essential to life, so the recent discovery suggest the possibility of finding life on Mars.