On its second flyby of Mercury this year, and the fifth in space exploration history, NASA’s probe is expected to show not only a different face of Mercury, but also a different perspective on the three-decade long debates in the scientific world.

MESSENGER, which stands for MErcury Surface, Space ENvironment, Geochemistry, and Ranging, is the first spacecraft set to orbit planet Mercury, and has a 4.9-billion mile or 7.9-billion kilometer journey to complete, including 15 trips around the Sun, before reaching its final destination, scheduled to take place in 2011. By then, MESSENGER will have completed one fly past Earth, two past Venus and three past Mercury.

It took three decades for NASA to develop another probe capable of studying Mercury, after Mariner 10, the first probe that completed three flybys in the 1970s. MESSENGER’s mission was of particular importance, since more than half of Mercury’s surface continued to remain uncharted territory (Mariner 10 saw the same face of the planet on each flyby).

In January this year, on the first Mercury flyby in over three decades, MESSENGER recovered critical data on our Solar System’s innermost planet, in addition to capturing never-before-seen images of the planet’s surface.

On Earth, the information received from MESSENGER gave birth to a new round of debates about Mercury’s geological history, as well as its mysterious and uniquely large core, which apparently still powers the planet’s magnetic field.

On that first flyby, MESSENGER sent back data on Mercury’s volcanic activity, which is believed to have been responsible for shaping the smooth plains that Mariner 10 mapped over 30 years ago. Furthermore, with the help of instruments onboard, MESSENGER indicated that Mercury’s core, that scientists believed to be a frozen relic, could in fact still be active, powering what John Hopkins University Applied Physics Laboratory (APL) Brian Anderson called a modern dynamism.

On this second flyby, scientists hope to find out even more about the planet’s puzzling magnetic field and apparently active core, and about the planet’s tendency to contract, several times greater than previously thought.

MESSENGER is expected to return over 1,200 high-resolution and color images and cover 30 percent more of the planet’s surface, which hasn’t been seen by a probe yet, on an opposite side from the first flyby. In January, MESSENGER’s images covered 20% of Mercury’s surface that scientists had never seen before.

With the help of its Mercury Laser Altimeter (MLA), NASA’s spacecraft will return data on Mercury’s topography. APL’s Brian J. Anderson explained that unlike the data obtained on the first flyby, which covered unknown territory, these measurements will cover areas photographed earlier in January.

One major goal for this flyby is to obtaine more details on Mercury’s surface composition, which will be possible though its Visible-Infrared Spectrograph (VIRS) on the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), the X-Ray Spectrometer, and the Gamma-Ray and Neutron Spectometer.

“In addition to providing data that are already being used to start answering the guiding science questions of the mission, the observations made during the Mercury flybys are critical to the science planning effort,” MESSENGER Project Manager Peter D. Bedini, of APL, explained. “The performance of the spacecraft and instruments during the flybys helps us prioritize and organize the observations to be made during the orbital phase.”

MESSENGER, which was launched on August 3, 2004, will start a year-long orbital study of Mercury in March 2011. In the meantime, NASA scientists prepare to feast their eyes on the first images from Mercury sent by MESSENGER.