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MErcury Surface, Space ENvironment, GEochemistry and Ranging

Phase: Operating

Launch Date: August 03, 2004

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MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) is a scientific investigation of the planet Mercury, the least explored terrestrial planet.

MESSENGER, with its seven instruments, will be the first mission to orbit Mercury and only the second mission to visit this planet closest to the Sun. Understanding Mercury and its history is essential to understanding the origin and evolution of the other terrestrial planets. To get into orbit around Mercury, it must follow a complex path through the inner solar system, using one flyby of Earth, two flybys of Venus, and three flybys of Mercury for gravity assists. This impressive journey has already returned the first new data from Mercury in more than 30 years from its January 14, 2008 flyby.

MESSENGER Mercury High-Res
Mercury’s previously unseen side
MESSENGER’s first Mercury flyby saw about half of the hemisphere of the planet unseen by Mariner 10 in its 3 flybys in the 1974-1975. This first MESSENGER image shows Mercury to be a unique and complex planet, quite unlike the moon to which it has commonly been compared.
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER launched on August 3, 2004, returned to Earth for a gravity boost on August 2, 2005, then flew past Venus on October 24, 2006 and June 5, 2007. It completed the first of three Mercury flybys on January 14, 2008 and will return on October 6, 2008 and September 29, 2009. The spacecraft uses these planetary flybys to resize and rotate its trajectory in order to achieve orbit around Mercury in March 2011. The Mercury flybys will also map the unseen side of the planet and yield science data to guide planning for the year-long orbital mission. MESSENGER’s instruments will map nearly the entire planet in color, image the surface in high resolution, and measure the composition of the surface, atmosphere and nature of the magnetic field and magnetosphere.

Mercury, Venus, Earth, and Mars are terrestrial (rocky) planets. Among these, Mercury is an extreme: the smallest, the densest (after correcting for self-compression), the one with the oldest surface, the one with the largest daily variations in surface temperature - and the least explored. Understanding this "end member" among the terrestrial planets is crucial to developing a better understanding of how our own Earth formed, how it evolved, and how it interacts with the Sun. To develop this understanding, the MESSENGER mission, spacecraft, and science instruments are focused on answering six of the key outstanding questions that will allow us to understand Mercury as a planet:

  1. Why is Mercury so dense?
  2. What is the geologic history of Mercury?
  3. What is the structure of Mercury's core?
  4. What is the nature of Mercury's magnetic field?
  5. What are the unusual materials at Mercury's poles?
  6. What volatiles are important at Mercury?



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