Washington - NASA's Messenger spacecraft came within just 200 kilometres of Mercury early Monday, taking pictures of the rocky planet nearest the sun.

It was the second of three planned flybys for the craft, which is due to settle into orbit around Mercury in 2011, providing what scientists hope will be the most complete picture yet of the solar system's smallest planet.

The 0840 GMT flyby was designed largely to pick up a gravitational boost of energy for the craft. It will begin beaming data back to Earth on Wednesday, NASA and university researchers said.

Data from Messenger's first flyby in January showed massive lava flows had shaped the planet and provided the first information on 20 per cent of Mercury's surface.

In 1974-75, the NASA probe Mariner 10 made three passes by Mercury, giving space scientists their first information about the planet's magnetic field.