Two Mars rovers, Opportunity and Curiosity, have been working overtime in recent years, with spectacular results.
March 24, 2015, NASA announced that the rover Opportunity had completed a 26-mile trek, the equivalent of a Martian marathon. It took just over 11 years.
Opportunity rover's robotic arm is like a Swiss army knife of scientific can-do. It includes two spectrometers, a microscopic imager, particle-collection magnets, and a rock abrasion tool that scrapes up fresh material.
Curiosity rover also has an array of cool functions. But, as demonstrated in this 2010 portrait at NASA's Mars Science Laboratory, it's only about the size of a Mini Cooper.
This photo, released by NASA on June 23, 2014 shows a self-portrait by the Curiosity Mars rover.
The Curiosity rover performed a tricky, daredevil landing on Mars in 2012 -- a feat later described by the Mars Science Laboratory team as "Seven Minutes of Terror." The successful landing prompted celebrations among the earthbound.
Opportunity rover has been working for its Earthlings for more than a decade without a vacation. In 2005, Opportunity found an iron meteorite. Dubbed Heat Shield Rock, it's the first meteorite of any type ever identified on another planet.
Just like your SUV, Curiosity rover has a rear cam for hazard avoidance. This was the view from that cam as Curiosity drove over a Martian dune on Feb. 6, 2014.
The wheel treads on Curiosity rover (seen in this photo from Oct. 3, 2012) have several functions: They maintain traction, but they also leave patterns used by on-board cameras to judge the distance traveled. (The pattern itself includes Morse code for "JPL.")
Opportunity rover is solar powered, so it’s environmental -- something future Mars residents will surely appreciate.
Both Opportunity and its defunct rover sibling, Spirit, have metal pieces of the fallen World Trade Center on them. The metal was fashioned into shields to protect drilling mechanisms.
Curiosity doesn't just explore. It cleans, using a wire brush. The result: Scientists can more clearly see rocks like this one, called "Bonanza King."
It drills, too
Curiosity has a drill that can bore for mineral samples, analyze them, and beam the results to Earth. (A sample of the drill work can be seen in this NASA pic.) Those analyses already have fueled speculation about the past and future of the Red Planet.
Opportunity rover studies Mars craters so you don't have to. It was the first to visit the crater Victoria (seen in the upper left in this NASA handout) and has been studying the makeup of the larger Endeavour crater.
That nice-looking dot on the Martian surface? Mars Curiosity, photographed via satellite in 2014. The rover was exploring for signs of water at the base of Mount Sharp near a feature called "Whale Rock."
Opportunity rover has looked a comet in the eye. In 2014, it captured images of comet Siding Spring. The comet's path came much closer to the Red Planet than any previous known flyby of Earth or Mars.
Curiosity is already inspiring a new generation of rovers. This NASA graphic shows the Mars 2020 Rover, featuring seven planned instruments. The $1.9 billion rover will even include an experiment that will turn carbon dioxide in the Martian atmosphere into oxygen.