Atmosphere of Mercury Atmosphere of Mercury Mercury has a very tenuous and highly variable atmosphere (surface-bound exosphere) containing hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10 bar (1 nPa). The exospheric species originate either from the Solar wind or from the planetary crust. Solar light pushes the atmospheric gases away from the Sun, creating a comet-like tail behind the planet. The existence of a Mercurian atmosphere had been contentious before 1974, although by that time a consensus had formed that Mercury, like the Moon, lacked any substantial atmosphere. This conclusion was confirmed in 1974
A Town Called Mercy called the Gunslinger. However, the Gunslinger is a product of experiments by Jex to win a civil war on his planet, and the Doctor is unsure of what is the right thing to do. Showrunner Steven Moffat pitched the Wild West theme to Whithouse when thinking of ways to give each episode a distinct theme. Whithouse further developed the theme, including classic Western tropes and a sympathetic villain. "A Town Called Mercy" and the previous episode "Dinosaurs on a Spaceship" were the first to enter production for the seventh series. Much of the episode was filmed in March 2012 in