Two satellites developed in Europe and Japan are on their way to the Sun’s closest planet Mercury.
It is likely to take them seven years to reach their destination.
The joint endeavor BepiColombo left Earth on an Ariane rocket that launched out of South America on Friday, the BBC said.
The probes lifted clear of the Kourou spaceport in the Atlantic coast of French Guiana at 10.45 pm on Friday.
Science has not yet explained why the planet only has a thin veneer of rocks.
Bepi’s high-resolution data should bring us nearer to an answer, the BBC reported.
It’s the first time the European and Japanese space agencies (ESA and JAXA) have set out for Mercury.
The Americans have already been there, briefly with the Mariner 10 probe in the 1970s, and with the Messenger orbiter earlier this decade.
Messenger discovered that water-ice is held inside some of Mercury’s shadowed craters and that its crust contains a lot of graphite (pencil lead). Bepi will build on those.
The new mission carries twice as much instrumentation and will get closer for longer.
Mercury’s dense body does not reflect its initial form. It’s possible the planet began life much further and later migrated inwards, mission scientist Suzie Imber from Leicester University.