NASA's Messenger probe, which was launched in August 2004, is all set to enter into orbit around the planet Mercury- the planet closed to the Sun.

The spacecraft is expected to make orbital insertion maneuver at around 8:45 p. m. on Thursday, after completing a harrowing 4.7 billion miles journey. By 2:47 a. m. EDT on Friday, it is expected to initiate its first complete orbit around Mercury.

The $446 million mission will provide detailed map of the surface of Mercury and allow scientists to examine the planet's magnetic environment, composition and tenuous atmosphere, among with other features.

Speaking on the topic, Messenger mission systems engineer Eric Finnegan said, "For the first two weeks of orbit, we’ll be focused on ensuring that the spacecraft systems are all working well in Mercury’s harsh thermal environment.”

Spacecrafts arriving at orbit around planets like Mars can slow down by sliding through planets' substantial atmospheres, a process which is called aerobraking. But, Messenger can not do that as Mercury's atmosphere is awfully thin & weak.

Mercury, the smallest of all the four rocky planets of the solar system, has so far been visited only by one spacecraft NASA’s Mariner 10 in 1974 and 1975.