WASHINGTON - THE US space probe MESSENGER's third and final fly-by of the planet Mercury in September revealed an almost complete view of the solar system's smallest planet, leaving only the polar regions to be surveyed, Nasa said.

Flying at a low altitude, the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) probe's cameras have now mapped some 98 per cent of Mercury's surface, and will complete the job after settling into permanent orbit in 2011.

Although the region viewed in September for the first time by spacecraft 'was less than 563km across at the equator, the new images reminded us that Mercury continues to hold surprises', said Sean Solomon, principal investigator from the Washington-based Carnegie Institution.

Using revolutionary image-capturing technology and a laser altimeter to survey the ground, MESSENGER revealed at close-range regions of the mysterious planet like never before.

Among the details collected during the latest fly-by, the probe captured images of large double-ringed impact basin about 290km across, Nasa said this week.

The third survey also revealed an abundance of iron and titanium on the planet's surface, a surprise for the mission because the two previous fly-bys, earlier this year and in late 2008, observed a low concentration of such materials. -- AFP