Europe's 'flying fridge" to explore Mercury is unveiled Scientists hope BepiColumbo can begin to unravel some of the mysteries about Mercury, such as what the blue-coloured flat bottomed hollows that pockmark the planets surface are made of. David Rothery said: "Mercury is the least known of the rocky planets in our solar system, but it is has an extraordinary surface. There appears to be areas where the surface is vaporising leaving hollows that are up to 10-20 metres deep with flat bottoms. We just don't understand it, as there is no wind or atmosphere or surface erosion on Mercury so what is doing that? It is also the closest to our sun, which could help us understand some of the planets we are discovering orbiting around other stars as they tend to be the closest to their stars because they are the easiest to spot. BepiColumbo will be the third spacecraft to visit Mercury but will also be the largest. In 1974 Nasa's Mariner 10 probe flew past the planet on its journey around the solar system and last year Nasa's Messenger spacecraft entered orbit around the planet. Crammed inside a bus sized "transfer vehicle," there will be two spacecraft put into orbit around Mercury as part of the BepiColumbo mission - the European Space Agency's planetary orbiter and a Japanese spacecraft that will measure the planet's magnetic field. ESA's orbiter will take some of the most detailed images of the planet's surface and also take x-ray images to work out what the surface is made of. In total the mission is expected to cost more than £700 million and is due to be launched in 2014, taking six years to reach Mercury. Jessica Marshall, a spacecraft systems engineering at Astrium, said one of the biggest challenges in building ESA's orbiter was ensuring it would be able to withstand the extreme temperatures it will face while in orbit around Mercury. Special testing facilities had to be built to blast the orbiter's heat shields and coolant systems with heat to ensure they will work and the mission has been delayed by a year as engineers have struggled to overcome the problems they faced. Miss Marshall said: "The whole spacecraft is a funny shape because we had to build this large radiator panel to ensure it stays cool. There will be heat coming from the sun and radiating off Mercury itself. We have to cool it down from these extreme temperatures to something approaching room temperature, while some of the imaging equipment needs to work at -100 degrees C (-148F). Every 44 days, which is the time it takes to do half an orbit, the spacecraft will also have to flip itself to make sure the radiator panel stays pointing out into space - if it does end up pointing at the sun then the instruments will be finished.