BepiColombo, Europe’s first mission to Mercury, will use a host of instruments on two orbiters to unravel the planet’s mysteries.
After launch, the spacecraft will take seven years to reach the scorching planet closest to the sun.
It will then deploy two probes packed with sophisticated technology.
The Mercury Planetary Orbiter (MPO), built in Britain, will study Mercury’s surface and composition while the Japanese Mercury Magnetospheric Orbiter (MMO) focuses on the electromagnetic environment surrounding the planet.
A key instrument on the MPO, the Mercury Imaging X-ray Spectrometer (Mixs), was developed and built at the University of Leicester.
The 13kg (28lb) metre-long device consists of two X-ray telescopes, one designed to capture images of the surface and the other to analyse its composition.
The planet is bombarded by high energy sub-atomic particles from the sun, causing the surface to “fluoresce” and emit X-rays.
Written into the rays are the “fingerprints” of atoms, and analysing them provides information about what the planet is made of.
Mixs scientist Professor Emma Bunce said there were “interesting quirks” about Mercury that scientists still did not fully understand.
Nasa’s 2011 Messenger mission to Mercury supplied some answers but “also raised more questions”.
One of the planet’s peculiarities was its unusually large iron core, which takes up much more room than the iron hearts at the centre of Earth, Mars and Venus.
Prof Bunce said: “It suggests that something dramatic happened early in Mercury’s evolution, like a massive impact with another body that stripped away most of the mantle.
“However, one thing Messenger taught us is that there are many volatile substances on Mercury’s surface. This is a puzzle because the heat of a major impact should have burned these volatiles away.
“One of the things we’re looking at is a much more detailed study of volatile substances like sodium, potassium and chlorine.”
Another Mercury mystery is the fact that X-ray fluorescence occurs on the planet’s “dark side”, despite the lack of sun.
Scientists believe they must be generated by a different process from the one on the sunlit side.
“The X-rays on the dark side appear to be organised and channelled by the magnetic field,” said Prof Bunce. “Electrons from the magnetosphere are channelled along, impact the surface, and fluoresce X-rays.
“It’s a bit like an aurora on the surface. That’s really exciting – it’s a really unusual scenario in the solar system that we can study.”
To protect Mixs from the searing 350C heat, the instrument’s finely crafted lenses are coated in aluminium, and the frame holding the optics in place is covered by a thin layer of 22 carat gold.
Prof Bunce added: “We want to understand how the solar system works and how it was formed. Mercury is a place of extremes; a small planet and the planet closest to the sun. Knowing how it has survived will help us piece together a bigger picture of the solar system and our place in it.”
The Messenger mission was limited by the fact that it used one orbiter and only covered Mercury’s northern hemisphere.
BepiColombo would map the entire surface, said Prof Bunce.
She was sure the wealth of science and technological spin-offs from the mission justified its 1.6 billion euro (£1.4 billion) price tag.
“A billion pounds is what it takes to build a fairly short stretch of motorway, say from Leicester to Birmingham, and we’re trying to answer fundamental questions about our solar system,” she said.
Prof Bunce admitted to having mixed feelings as the countdown to the launch continued.
“It’s extremely exciting but also a little bit terrifying,” she said.
“There’s so much work our engineering and technical team has put into it over the past decade – all that blood, sweat and tears invested in that instrument sitting on the top of a rocket. It will be great to see it get on its way.”