The American spacecraft Messenger was launched to Mercury aboard a Boeing Delta II. The probe weighed just 1,100 kg, including 600 kg of propellant in titanium tanks only 0.5 mm to 1 mm thick. Thanks to its carefully designed orbit, it achieved the unprecedented feat of entering orbit around Mercury in 2011, escaping the fatal pull of the nearby Sun. Combined with the complete success of Mariner 10, this made them the only two missions to Mercury in half a century, making Mercury the only rocky planet in the Solar System with a 100% success rate.
