BepiColombo is due to be launched from the European space port at Kourou, French Guiana, at 0245 UK time (1245 AEDT) on Saturday.

The European Space Agency (ESA) spacecraft will take seven years to reach the planet closest to the sun.

In 2025 it will place two probes, one European and the other Japanese, in orbit around Mercury, the least explored world in the solar system.

Scientists hope the PS1.4 billion mission will unravel some of Mercury's mysteries, such as the reason for its oversized iron core, its spectacular volcanic vents, and tantalising hints of water ice in shadowy parts of the scorching hot planet.

The answers they get will shed new light on the origins and evolution of the solar system.

A key feature of BepiColombo is that it is the first interplanetary mission to employ advanced electric ion propulsion technology.

Four Star Trek-style "impulse engines", two firing at a time, will emit beams of electrically-charged, or 'ionised' xenon gas.

They will be used not to accelerate the craft but to act as a brake against the sun's enormous gravity.

A complex series of fly-bys past the Earth, Venus, and Mercury will also help to reduce BepiColombo's velocity by 7km per second.

At top speed after launch, the spacecraft will be moving at 60km per second.

One of the biggest challenges for mission planners was ensuring the spacecraft could withstand searing temperatures of more than 350C so close to the sun.

Protective measures include a heat shield, novel ceramic and titanium insulation, ammonia-filled "heat pipes", and in the case of the Japanese orbiter, "roast-on-a-spit" spinning.

A suite of 11 instruments on the MPO will map the surface of Mercury and probe its chemical composition for up to two years.

Meanwhile, the Japanese space agency Jaxa's Mercury Magnetospheric Orbiter will focus on the planet's unusual magnetic field.

Only two spacecraft have previously visited Mercury. Nasa's Mariner 10 flew past the planet three times in 1974-75 and the American space agency's Messenger probe orbited Mercury from 2011 to 2015.

BepiColombo was named after the late Giuseppe "Bepi" Colombo, an Italian scientist and engineer who played a leading role in the 1974 Mariner 10 mission.

Australian Associated Press