For the first time in over 30 years, a spacecraft from Earth flies past the innermost planet, Mercury. The Messenger space probe, launched in 2004, is due to take up an orbit around Mercury in 2011, but this first close pass – just over 120 miles above Mercury’s surface – is designed to alter its trajectory. Messenger carries little fuel, and has swooped past Earth three times and twice past Venus to use both planets’ gravity to change its heading. Two more close passes of Mercury will be needed before it finally becomes caught in the tiny planet’s orbit, where it will spend roughly a year mapping the planet’s surface and taking dozens of other measurements. The last space probe from Earth to visit Mercury was Mariner 10, which made three close passes in 1974/75. Despite the brief gravity-assist visit, Messenger captures its first 1,200 images of Mercury, including a side of the planet never before seen from Earth.
