The rocket launch is scheduled to take place at 2.45am United Kingdom time (1.45am UTC) from French Guiana.
Mission controllers based in Darmstadt, Germany, would spend much of Saturday talking to the spacecraft, to confirm they were properly configured for the long cruise ahead.
"After months of practice, teams here at mission control are eager to see BepiColombo depart from our planet, and they're ready to guide it carefully every day for seven years until it arrives at Mercury".
Meanwhile, the planet's proximity to the sun with the extreme temperature between 180 degree Celsius to over 450 degree Celsius makes the spacecraft trip challenging, the ESA noted.
According to the website of the ESA, BepiColombo is a joint project of the European space Agency and Japanese aerospace exploration Agency, worth 1.85 billion dollars. JAXA's Mercury Magnetospheric Orbiter, nicknamed Mio, will study the planet's magnetic field and Mercury's atmosphere.
A powerful European Ariane 5 rocket was primed for blastoff Friday evening to send a pair of satellites on a seven-year voyage to Mercury.
European Union rejects Italy's budget, raising stakes in dispute
We know that if we would give up, that the experts for the banks and austerity would return. Brussels was only angering Italians even more and eroding faith in the bloc, he warned.
The MMO will make as its priority the study of the planet's magnetic field.
A seven-year, eight-million-kilometer voyage expected to shed light on the mysteries of Mercury, the solar system's least-understood planet, is almost ready for takeoff.
A combination of spacecraft will be launched together, with the Mercury Composite Spacecraft (MCS) consisting of two orbiters: MMO, MPO; as well as two additional elements: MTM, the Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF).
The mission is primarily composed of two orbital craft, one each developed by ESA and JAXA. Though current plans call for a single year of research, the spacecraft are created to operate in a research mode for two years, he said. Because of its its proximity to the sun, it's difficult to observe with ground telescopes and hard to reach via spacecraft. "To understand how Earth was formed, we need to understand how all rocky planets formed".
Airbus in the United Kingdom built large parts of the MPO and the mission's propulsion unit, called the Mercury Transfer Module (MTM).
Even if BepiColombo only partially fulfills its objectives, the knowledge that researchers gained in designing and launching the spacecraft will be applied to future missions.
Astronomers and space-themed editorials have long speculated that the mission to Mercury may bring us closer in the search for alien life.
The Ariane 5 launched "Bepi" into space at "escape velocity" - the speed required for an object to break free of the Earth's gravitational pull. NASA's MESSENGER orbiter (2011-2015) revealed many reasons why scientists are keen to learn more about it. At its closest approach, Mercury is just 77 million kilometers from Earth, or not all that much further than the closest that Earth comes to Mars.