Mars is back. Suddenly everyone - from Elon Musk to Ridley Scott to Donald Trump - is talking about going to the Red Planet.
When the Apollo astronauts walked on the Moon in 1969, many people imagined Mars would be next. However NASA's Viking 1, which landed in 1976, was just a robot. The much-anticipated crewed mission failed to materialise, defeated by a combination of technological and political challenges.
Four decades...