OPPORTUNITY: The rover, designed to last 90 days, landed on Mars in 2004, and was still going further until a planet-encircling storm storm struck in June. NASA has been trying to revive the rover since the dust storm ended using both listening and command methods, the agency said in October. Engineers believe it's possible that a layer of dust on the rover's solar panels is blocking sunlight that it needs to recharge its batteries. They have not given up hope, especially since winds that typically occur in the November-to-January time frame have helped clean the rover's panels in the past. In any case, the six-wheeled rover has exceeded its expected life span many times over.
SPIRIT: Opportunity's twin was also expected to last in Mars' extreme winters and dust storms only 90 days. But Spirit got stuck in sand and ceased functioning in 2009. Like Opportunity, it landed on Mars in 2004, and in its nearly six-year mission returned about 124,000 photographs from the surface of the planet's red. Spirit is made in part of aluminum recovered from the site of the World Trade Center, the towers in New York City that were destroyed in the terrorist attacks on September 11, 2001.
PHOENIX LANDER: This stationary probe touched down in the Martian Arctic in May 2008 and surpassed its original three-month mission, lasting five months. The Phoenix lander targets a circumpolar region and used a robotic arm to dig, scoop, bake, sniff and taste the planet's soil. Among early results were verification of the presence of water-ice in the Martian subsurface.
CURIOSITY: The 2.5-billion-dollar, more modern and technically capable rover landed on Mars in August 2012. It started its exploration inside Gusev Crater, a region where in the past liquid water was abundant. The newer rover has made numerous discoveries, including that ancient Mars could have supported living microbes. It is powered by a plutonium generator, so its operations were not affected by the dust storm in June. Earlier this month it drove about 60 meters, pushing its total distance moved to more than 20km. He experienced a "memory anomaly" in September that engineers continue to diagnose.
HUMANS TO MARS: NASA's dream of flying humans to Mars is a mission that is very alive and rests on its next-generation space capsule Orion. NASA has sent the Orion space capsule on test flights atop Delta IV Heavy Rocket. NASA's long-term plan calls for landing astronauts first on an asteroid and then later on Mars sometime in the mid 2030s.