A UK-built spacecraft is set to fly off the Earth to fly to Mercury, the mysterious planet that is the Sun's sun next is.
BepiColombo, one of the most ambitious missions ever undertaken by the European Space Agency (ESA), will send two orbiters to explore the hellish world, where the surface temperature reaches 450C.
A probe was built by the satellite manufacturers Airbus Space and Defense at their assembly center in Hertfordshire. The other was built in Japan. The mission, which started on Saturday, cost an estimated £ 1
Unlike other interplanetary spaceships in history, BepiColombo carries a futuristic ion propulsion system, also developed and built in the UK.
Four ion engines on the Mercury Transfer Module that transport the orbiters provide thrust by electrically discharging a "plasma" of charged xenon gas.
Although the force generated by an ion motor is very small, it can continue to be ignited for a long time. The four-ton spacecraft will be escorted by Esa's most powerful rocket, the Ariane 5, from the European Spaceport in Kourou, French Guiana.
Then it's a seven-year, 5.2 billion-mile journey.