NASA plans to launch a spacecraft to Mercury in early August for a study of the heavy-metal planet's surface to determine its composition and to see if there is ice on it.

The Messenger spacecraft is set for launch on Aug. 2 on a seven-year journey. After flying some 7.9 billion km in space, the craft is expected to enter Mercury's orbit in March 2011.

"Understanding Mercury, and the forces that have shaped it, is fundamental to understanding the terrestrial planets and their evolution," NASA said in a statement on Wednesday.

Mercury, the first planet from Sun, is very unusual among the inner terrestrial or rocky planets, which include Earth, Venus and Mars. The smallest planet is the densest, and scientists believe at least two-thirds of it must be made up of iron.

In addition, Mercury is the one with largest daily variations in surface temperature. The temperature difference between day and night on the least explored planet is up to 600 degrees Celsius, with a daytime temperature around 450 degrees Celsius.

As the interiors of large craters at Mercury's poles are permanently shadowed and remain always cold, below 212 degrees Celsius, scientists believe ice may exist there. Previous radar images of the polar regions show that the large craters' interiors are highly reflective, which suggests a possible presence of ice.

Scientists also hope the 426 million-US dollar Messenger mission can help them to know more about Mercury's geologic history and the structure of its core among other things.

Source: Xinhua