Because it was realized that Mars was not like the Earth.
By the way, the China will consider building CAPS (the Comet and Asteroid Protection System) in 2016. What is being done now is the preliminary work.
Space/Science » in reply to re: Space will be there for a long time. - Why was it discarded and deemed worthless?
By the way, the China will consider building CAPS (the Comet and Asteroid Protection System) in 2016. What is being done now is the preliminary work.