Japan Aerospace Exploration Agency astronaut Aki Hoshide makes a space walk outside the International Space Station in 2012. NASA/Getty Images hide caption

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NASA's MAVEN, short for Mars Atmosphere and Volatile Evolution, with a capital "N" in EvolutioN, atop a United Launch Alliance Atlas V rocket, lifts off from Cape Canaveral Air Force Station, on Monday. John Raoux/AP hide caption

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Scientists and engineers work on the Mars Orbiter at the Indian Space Research Organisation's satellite center in Bangalore, India, on Sept. 11. The spacecraft is scheduled to be launched sometime in the next three weeks. Manjunath Kiran/AFP/Getty Images hide caption

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A photo composed of nearly 900 images taken by the rover Curiosity shows a section of Gale Crater near the equator of Mars. The rovers are continuing to work through the U.S. government shutdown. NASA/AP hide caption

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The rover Curiosity and other NASA spacecraft at Mars are now in a radio blackout, as the sun is interfering with transmissions. Curiosity took this self-portrait by combining 66 exposures in February. NASA hide caption

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Will we need to tread lightly, in deference to the locals, when finally do make it to Mars? Pat Rawlings/SAIC/NASA hide caption

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Coprates Chasma in the Valles Marineris on Mars, photographed by the Mars Express spacecraft. Appearing in the top half of this image, it ranges from 60-100 km wide and drops 8-9 km below the surrounding plains. G. Neukum/ESA/DLR/FU Berlin hide caption

itoggle caption G. Neukum/ESA/DLR/FU Berlin