Space officials in the United States and Europe are planning an ambitious dual-rover mission that could start collecting Martian soil samples in 2018 to be picked up by a subsequent mission and returned to Earth in the 2020s. The costly mission would blast off on an Atlas 5 rocket in 2018 and land two rovers on Mars with a single “sky crane” descent system that will be tested for the first time at the Red Planet in August 2012. It would be the first time two rovers will be delivered to the same landing site on Mars. The European Space Agency’s ExoMars rover and a $2 billion NASA Mars Astrobiology Explorer-Cacher mission are the leading candidates for the tandem project.