OPPORTUNITY: The rover, designed to last 90 days, landed on Mars in 2004, and was still going more until a planet-encircling dust storm hit 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 is possible that a layer of dust on the rover's solar panels is blocking the sunlight that it needs to recharge its batteries. They have not given up hope, especially because 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 expected to last in Mars' extreme winter and dust storms only 90 days. But Spirit got stuck in the sand and stopped operating in 2009. Like Opportunity, it landed on Mars in 2004, and in its nearly six-year mission returned about 124,000 photos from the surface of the red planet. Spirit is made of aluminum, recovered from the site of the World Trade Center, the towers in New York City that were destroyed in September 11, 2001 by terrorist attacks.
PHOENIX LANDER: This stationary probe touched on the Martian arctic in May 2008 and surpassed its original three-month mission, lasting five months. The Phoenix lander targeted and circumpolar region and used a robotic arm to dig, scoop, bake, sniff and taste the planet's soil. Among early results were the presence of water-ice in the Martian sub-surface.
CURIOSITY: The 2.5 billion-dollar, more modern and technically capable rover landed on Mars in August 2012. It began its exploration within the 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. It experienced a "memory anomaly" in September that engineers continue to diagnose.
HUMANS TO MARS: NASA's dream of flying people to Mars is a mission that is very much alive and rests on its next-generation space capsule Orion. NASA has sent the Orion space capsule on test flights to the 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.