Mercury 4 or variants may refer to: Mercury 4, a spacecraft of Project Mercury Mercury4, an Australian boy band 2002–2004 Mercury(IV), an unknown compound of the element Mercury Mercury IV, a 1929 version of the Bristol Mercury aircraft engine See also Mercury (disambiguation) Mercury-Redstone 4, the second U.S. human spaceflight, 1961 Mercury-Atlas 4, a 1961 unmanned space flight