European and Japanese scientists yesterday proudly unveiled the BepiColombo spacecraft ahead of its seven-year journey to Mercury, to explore one of the Solar System's most enigmatic planets.

Set for launch in 2018, BepiColomho will be the European Space Agency's (ESA) fust mission to the closest rock to the Sun.

The craft has an unusual design, comprising a 'stacked aircraft' carrying two orbiters -- one European, the other Japanese -- which will separate on arrival to go into different, but complementary orbits around Mercury.

BepiColombo aims to "follow up on many of the intriguing results of Nasa's Messenger mission, probing deeper into Mercury's mysteries than ever before," the ESAsaid.

The joint project with the Japanese agency JAXA which has cost more than 1.3 billion euros ($1.48 billion), involves some 33 companies from 12 EU nations, as well as firms from the US and Japan.

It has been delayed several times, but the mission chiefs are now confident that it is on track to launch in October next year.

Mercury is the “most peculiar of all rocky planets,' Alvaro Gimenez, ESA's director of science told reporters at the agency's centre in the Dutch coastal town ofNoordwijk.

Its surface is wracked by extreme temperatures, ranging from +450 to - ISO degrees Celsius (+842 to -292 degrees Fahrenheit).

It also has a magnetic field, the only rocky planet besides Earth to have one.

But Mercury is so weak that the field does not provide a shield against solar radiation.

It orbits just 58 million kilometres (36 million miles) from the Sun, and its surface is blasted by radiation levels that would destroy earthly Its proximity to the Sun also makes Mercury hard to study from Earth because the brightness impedes the view. The Sun's huge gravity also makes it difficult to put a craft into steady orbit around the

The high temperatures also presented tricky challenges for the engineers, which include the European aircraft designer Airbus, and added to project delays, mission chiefs said.