In 2012, the Mars Science Laboratory (MSL)  successfully touched down on the Red Planet. Aptly named Curiosity, it brought with it scientific discovery instruments and exploration capabilities that only a nuclear-powered rover could realistically possess.
While not the first rover to successfully land on Mars, a distinction that goes to Sojourner deployed by the Mars Pathfinder in 1997 and followed by the wildly successful Mars Exploration Rover (MER) pair Spirit and Opportunity that landed in 2004 , Curiosity was the first rover powered by nuclear energy.
Much like the MERs exceeding their planned 90-day mission life by 2500+ Martian days (sols) in the case of Spirit and 5000+ in the case of Opportunity; Curiosity has also far exceeded its original two-year mission lifespan by many years and is still going strong. All of these rovers are a testament to American engineering prowess and demonstrate the benefits of a robust space exploration manned or otherwise. As Curiosity heads into its 7th year it is continuing to yield significant insight in Mars' history, geology, and whether the planet could have supported life sometime long ago. However, what sets Curiosity apart from Sojourner, Spirit, or Opportunity is its power source. Curiosity is powered by a multi-mission radioisotope thermoelectric generator (MMRTG) whereas Sojourner, Spirit, and Opportunity were all solar-powered. Mars is significantly further from the sun than Earth is, which makes solar power a challenge; harsh weather conditions especially during the Martian winter can render a rover powerless for months on end and Martian dust can degrade solar cell performance. Rather than utilize the sun, the RTG in Curiosity utilizes the heat emitted from a decaying plutonium isotope to generate electricity via thermocouples. In addition to improving the performance of the rover in the harsh Martian climate, this RTG has also allowed Curiosity to be significantly larger (nearly the size of a Mini Cooper) than its predecessors  and capable of carrying more tools and equipment. Curiosity boasts numerous cameras that have captured stunning Martian vistas over the past six years  and a robotic arm capable of zapping rocks and analyzing the debris for its chemical components.
In its six years roving the desolate Martian surface, Curiosity has greatly increased our understanding of Mars and its complex past. Just a few months after its landing in 2012, it found evidence of an ancient stream bed on the Martian surface , suggesting water once flowed along the surface. In 2013 Curiosity found evidence that Mars once contained conditions suitable for life  and also found evidence that appears to confirm the idea that the atmosphere Mars once had escaped into space . Curiosity continues to reveal what may be humanity's next stepping stone on its journey into the stars. More recently, Curiosity discovered the presence of organic molecules including methane on Mars, which is a significant development in the search for the possibility of life off of earth. While Curiosity's original mission mandate was fulfilled a year after landing, its current mission is open-ended, as long as the rover continues to function. With the current rate of decay of its RTG, it is expected to last nearly another decade  during which Curiosity's roving will likely yield further insight into the mysterious Martian past and help inform future-manned missions to the Red Planet
All that Curiosity has accomplished and will continue to accomplish has been made possible by the robust, safe, compact, 24/7 nature of its MMRTG. Nuclear-powered rovers will not stop with Curiosity. Indeed, the next Martian rover set to launch in 2020 will be a cousin of Curiosity and it will once again bring an RTG to the surface of the Red Planet. It is feasible that when the first humans land on Mars in the coming decades, their spacecraft will be powered by nuclear energy and they will recognize the significant impact that efficient nuclear power has had in allowing them to step foot onto another world.
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