WASHINGTON — A Mercury-bound science mission from the European and Japanese space agencies began a seven-year journey to the Solar System’s smallest planet Oct. 19 aboard and Ariane 5 rocket.

The BepiColombo mission took off from the European Spaceport in Kourou, French Guiana at 9:45 p.m. Eastern, marking the beginning of a 9-billion kilometer trip to the closest planet to the Sun.

BepiColombo’s four parts — two science orbiters, their carrier unit and a sunshield — separated as one 4,100-kilogram payload from the Ariane 5’s upper stage 27 minutes after liftoff. ESA confirmed signal acquisition shortly after separation from the Arianespace-operated launcher.

The spacecraft now begins a journey that includes nine planetary flybys for gravitational assists — one of Earth, two of Venus and six by Mercury — in order to safely arrive in orbit around the planet.

A direct trajectory to Mercury would give BepiColombo too much speed to not succumb to the sun’s gravity.

Once in Mercury’s orbit, BepiColombo’s carrier spacecraft will release the two orbiters, the European Space Agency’s Mercury Planetary Orbiter, and the Japan Aerospace Exploration Agency’s Mercury Magnetospheric Orbiter, to begin a one-year science mission.

BepiColombo is JAXA’s first joint mission with ESA, and both space agencies’ first mission to Mercury. The science mission builds on research from Mercury’s only two science missions: NASA’s Mariner 10, which performed three fly-bys in 1974 and 1975, and NASA’s Messenger, which orbited from 2011 to 2015 before crashing into the rocky planet’s surface.

ESA member states almost cancelled BepiColombo after the mission, which began in 2000, grew too large to fit in a Soyuz rocket, requiring a more expensive Ariane 5 to continue. In 2009 ESA approved the redesigned mission, featuring systems optimized for the extreme temperatures near Mercury, despite the increased cost.

Once at Mercury, ESA’s Mercury Planetary Orbiter will study the surface of the planet using a suite of 11 instruments. JAXA’s Mercury Magnetospheric Orbiter, equipped with five instruments, will study the planet’s magnetosphere and its interactions with the sun.

Airbus Defence and Space is the prime contractor for ESA’s part of BepiColombo, having led a team of 83 companies from 16 countries in building the Mercury Planetary Orbiter, the carrier module and sunshield. Japan-based NEC Corp. led an industrial team in building JAXA’s spacecraft.

Manufacturers for BepiColomobo had to build unique technologies, such as British company QinetiQ’s new, highly efficient electric propulsion system to slow the spacecraft, and German manufacturer Azur Space’s solar cells capable of generating power while enduring higher than normal temperatures.

Temperatures around Mercury range from 450 to -180 degrees Celsius (around 850 to -300 degrees Fahrenheit). Johannes Benkhoff, BepiColombo mission scientist at ESA, said 80 percent of the materials for BepiColombo needed to be specially qualified to ensure they could survive the mission.

BepiColombo is named after the late professor Giuseppe “Bepi” Colombo, from the University of Padua, Italy, who studied Mercury and suggested NASA fly its Mariner 10 orbiter by Venus for a gravity-assist, enabling the spacecraft to fly by Mercury three times.

BepiColombo is scheduled to arrive at Mercury in December 2025 and begin its science mission in 2026. Benkhoff said a decision will have to be made whether to fund the mission for an additional year. Though current plans call for a single year of research, the spacecraft are designed to operate in a research mode for two years, he said.