Messenger to unlock the mysteries of Mercury

The first space mission in 30 years to the planet Mercury, one of the hottest places in the solar system, is to begin this morning, when the Messenger spacecraft is launched from Cape Canaveral in Florida. The craft will take nearly seven years to reach its destination, a 4.9-billion-mile journey that loops around the Sun 15 times.

The first space mission in 30 years to the planet Mercury, one of the hottest places in the solar system, is to begin this morning, when the Messenger spacecraft is launched from Cape Canaveral in Florida. The craft will take nearly seven years to reach its destination, a 4.9-billion-mile journey that loops around the Sun 15 times.

Mercury is the nearest planet to the Sun and was last studied by the Mariner 10 craft in three fly-bys in 1974 and 1975. But Mariner 10 took pictures of less than half of Mercury's pock-marked surface. This time, the £234m Messenger will go into an egg-shaped orbit around the planet in the hope of answering many questions, such as how this intensely hot planet can retain what appears to be ice in its polar craters.

Mercury is the least-explored of the terrestrial or "rocky" planets, a group that includes Venus, Earth and Mars and is believed to be the oldest and densest of any of the solar system's nine planets.

Orlando Figueroa, the director of solar system exploration at Nasa in Washington, said studying the other rocky planets has given scientists great insights into how the Earth was formed. "Yet Mercury still stands out as a planet with a fascinating story to tell," he said. "Messenger should complete the detailed exploration of the inner solar system, our planetary backyard, and help us to understand the forces that shaped planets like our own."

Messenger will use a technique called gravity-assist to sweep it on its way to Mercury. It will use the gravitational pull of Earth, Venus and Mercury itself to sling the solar-powered spacecraft into its final orbit, which it is due to enter in March, 2011. David Grant, the mission's project manager at a division of Johns Hopkins University in Laurel, Maryland, said Messenger's seven instruments will be protected by a heat shield.

"After launch and a long trip through the inner solar system, we still face the risk and difficult job of orbiting the planet next to the Sun," he said. "The team is confident that the spacecraft they designed, built and tested is ready for this journey and its mission to Mercury."

Surface temperatures on Mercury can reach 450C. Named for the fleet-footed messenger of the gods in mythology, the planet is a third of the size of Earth and seems to be a world of huge craters, smooth plains and long, winding cliffs. It has an extremely thin atmosphere and a core of iron, which makes up some 60 per cent of the planet's total mass, twice as much as the iron core of Earth.

Only 45 per cent of the planet's surface has been photographed, so one of the first tasks of the Messenger spacecraft will be to take pictures of the missing parts. One of the greatest mysteries is finding whether there is ice hidden deep in the shaded craters of Mercury's polar regions.

Sean Solomon, the principal investigator on the mission, said. "For nearly 30 years, we've had questions that couldn't be answered until technology and mission designs caught up with our desire to go back to Mercury," he said. "Now we are ready."