MESSENGER, the MErcury Surface, Space ENvironment, GEochemistry and Ranging spacecraft launched by NASA in 2004, is scheduled to fly over Mercury in the first visit in almost 33 years to the mysterious small planet. This will be the first of four sweeps over Mercury by the MESSENGER, which will bring the probe some 120 miles from the planet's surface.

The sophisticated yet small MESSENGER probe prepares to fly by the hemisphere completely missed by the Mariner mission in the 1970s. NASA's gadget will send some 1,200 photos on Tuesday when it resumes communications with Earth. The spacecraft has already flown past Earth once and Venus twice as it spiraled down the solar system on the carefully calculated 4.9 billion-mile trek to Mercury.

"More than half the planet's never been seen before," said Messenger principal investigator Sean Solomon, of the Carnegie Institution of Washington. "That will change on Monday."

Launched on a Boeing Delta II rocket, MESSENGER lifted off from Cape Canaveral Air Force Station, Florida at 02:15:56 EDT on August 3, 2004 with the goals to determine the chemical composition of Mercury's surface, its geologic history, the nature of the planet's magnetic field, the size and state of the core, the volatile inventory at the poles, and the nature of Mercury's exosphere and magnetosphere.

"Now, we're just a few days away from our first glimpse of Mercury in 33 years," said Solomon. "It is an understatement to say that the science team is extremely excited."

However, MESSENGER's most important mission is yet to come: its Mercury orbit insertion will be on March 18, 2011, beginning a year-long orbital mission which will see a lot more data sent to Earth.

The space probe is also interesting because its navigation team is lead by KinetX, the first private company to be responsible for navigation of a NASA deep space mission. Their experts are fully responsible for determining all trajectory adjustments throughout the probe's flight through the inner solar system ensuring that MESSENGER arrives at Mercury with the proper velocity for orbit insertion.

Mercury, named after the Roman god Mercurius, is the innermost and smallest planet in the solar system and orbits the Sun every 88 days. The robotic space probe Mariner 10 was the only spacecraft to approach Mercury, and managed to map about 40 percent of its surface. Its mission ran between 1974 and 1975 and was the first spacecraft to make use of an interplanetary "gravitational slingshot" maneuver.