A spacecraft has achieved orbit around the planet Mercury for the first time, following an eight-billion-kilometre journey.

Surviving blistering heat from the nearby Sun with the help of ceramic shields, Nasa's Messenger probe began orbiting just 200km above the surface of the solar system's innermost planet on Friday.

At roughly half the weight of a small car, the probe - which began its journey almost seven years ago - will map the sizzling hot surface and investigate everything from its magnetic field to why it is so unusually heavy, despite its small size.

Scientists believe the results could provide clues to how the Earth and the solar system formed 4.5 billion years ago.

According to Nasa's website, for the next several weeks engineers will focus on ensuring systems are working well in Mercury's harsh environment. On March 23, the instruments will be turned on and checked out, and on April 4 the mission's primary science phase will begin.