TOKYO (Reuters) - A European-Japanese spacecraft set off on a treacherous seven-year journey to Mercury to probe the solar system’s smallest and least-explored planet. The BepiColombo mission, only the third ever to visit Mercury, blasted off from Europe’s spaceport in French Guiana aboard an Ariane 5 rocket at 10:45 p.m. local time on Friday (0145 GMT on Saturday), according to the Japan Aerospace Exploration Agency (JAXA). “Launching BepiColombo is a huge milestone for ESA (the European Space Agency) and JAXA, and there will be many great successes to come,” ESA Director General Jan Woerner said in a statement. “Beyond completing...