• Introduction



      The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission is a scientific investigation of the planet Mercury, the smallest and least explored of the terrestrial planets.  It has the oldest surface and thinnest atmosphere.  Temperatures vary from nearly the highest in the solar system to among the coldest.  It's the only planet besides Earth to possess a global magnetic field.  It has an enormous iron core that takes up at least 60% of its total mass – twice as high a fraction as for Earth.  Understanding Mercury and the forces that have shaped it is fundamental to understanding the origin and evolution of the four rocky inner planets in our solar system.



      Mission Management

      Dr. Sean C. Solomon
      Dr. Sean C. Solomon
      Principal Investigator

      The MESSENGER project is managed by The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD.  The Principal Investigator is Dr. Sean C. Solomon of the Carnegie Institution of Washington.  The spacecraft was built by APL.

  • Science Objectives
    • Mercury's previously unseen side
      Mercury's previously unseen side.

      Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

      MESSENGER's science goals are to provide the first images of the entire planet and collect detailed information on the composition and structure of Mercury's crust, its topography and geologic history, the nature of its thin atmosphere and active magnetosphere, and the makeup of its core and polar materials.

      With seven miniaturized instruments and the spacecraft communication system, the mission is focused on answering six key science questions:

      • Why is Mercury so dense?
      • What is its geologic history?
      • What is the nature of its magnetic field?
      • What is the structure of its core?
      • What are the unusual materials at the poles?
      • What volatiles are important?

      In November 2011, NASA announced it will extend the mission for an additional year of orbital operations at Mercury, allowing scientists to learn even more about the planet closest to the Sun. MESSENGER will spend more time close to the planet than during the primary mission and will make many more targeted observations.

      The extended mission is designed to answer six scientific questions, each of which has arisen as a result of discoveries made from orbit:

      • What are the sources of surface volatiles on Mercury?
      • How late into Mercury's history did volcanism persist?
      • How did Mercury's long-wavelength topography change with time?
      • What is the origin of localized regions of enhanced exospheric density at Mercury?
      • How does the solar cycle affect Mercury's exosphere and volatile transport?
      • What is the origin of Mercury's energetic electrons?

  • Details
    • spectacular color mosaic
      This spectacular color mosaic shows the eastern limb of Mercury as seen by MESSENGER following the first flyby in January 2008. The colors depict the varying types of rocks. Caloris basin, one of the largest impact craters in the solar system with a diameter of nearly 1,000 miles, is visible as a large bright yellow circular area due to its volcanic plains.

      Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington

      MESSENGER was launched August 3, 2004, aboard a Boeing Delta II rocket from Cape Canaveral Air Force Station, Florida. It returned to fly past Earth for a gravity assist one year after liftoff. After two flybys of Venus and three flybys of Mercury, it began a planned one-year orbit of the innermost planet on March 18, 2011. Because of its great success in returning incredible images of Mercury, including the first global close-up views, NASA has extended the mission for a second year of orbital operations.

      The MESSENGER mission takes advantage of a remarkable trajectory design, tough lightweight materials, and miniaturization of electronics, all developed in the three decades since Mariner 10 flew past Mercury in 1974 and 1975.  That early mission was the only previous spacecraft investigation of Mercury. 

      After MESSENGER's three flybys of Mercury, approximately 98% of the planet has been mapped in color, most of the areas not seen by Mariner 10 have been viewed, and MESSENGER has taken snapshot measurements of the composition of the surface and atmosphere and the structure and dynamics of the magnetosphere.  During the 12-month orbital period, MESSENGER will obtain global mapping data and focus on targeted science investigations.  










  • Results
    • Images and data reveal Mercury as a unique, geologically diverse world that is a lot less like the Moon than many previously thought.  An important finding is the recognition that volcanism has been widespread on the planet.  Smooth plains, mostly volcanic deposits, occupy at least 40% of the surface, and impact craters have excavated material similar to plains from depths as great as several miles.  A particularly young impact basin contains volcanic material on its floor, indicating that volcanism spanned a considerable fraction of Mercury's history.  Some volcanic deposits appear to be the product of explosive eruptions, providing evidence for volatiles in Mercury's interior.

      Unlike the Moon, Mercury has huge cliffs that wind hundreds of miles across the planet's face, tracing patterns of fault activity from throughout Mercury's history.  The cliffs are thought to be the surface expressions of large faults that record global contraction as the interior of the planet cooled over aeons.


      A few areas of Mercury show evidence of extension or stretching of the crust.  One such feature is a set of more than 200 narrow troughs that radiate outward from the center of the huge Caloris impact basin. Nothing like this feature, called Pantheon Fossae, has been observed elsewhere on Mercury or on the Moon.

      MESSENGER's neutron spectrometer has shown that Mercury's surface materials have a combination of iron and titanium similar to that in some lunar mare regions.  Unlike the Moon, however, Mercury shows no evidence in its spectral reflectance for iron-bearing silicate minerals.  Variations in color and reflectance among major terrains on Mercury can be fit by a varying mix of a bright, spectrally "red" plains material and a dark, spectrally neutral material that may consist of iron-titanium oxides.

      In addition, MESSENGER conducted the first laser altimetric profiles of Mercury, improved our understanding of the planet's magnetic and gravitational fields, discovered new constituents in Mercury's atmosphere, and demonstrated that Mercury's magnetosphere is much more responsive to changes in its environment than that of any other planet.

      For much more information on MESSENGER's science results, visit the Team Publications and Presentations areas of their website.

      a rimless depression that may feature an explosive volcanic vent This region shows evidence of a high level of volcanic activity. The bright yellow area near the top right is centered on a rimless depression that may feature an explosive volcanic vent. The double-ring basin in the center has a smooth interior that may be the result of effusive volcanism. Smooth plains from earlier volcanic activity cover much of the surrounding area.
      Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


      a large  ancient crater A long scarp, or cliff, visible from upper left to lower right, runs through a large ancient crater seen in the center of the frame. Similar scarps have been identified all over the planet, suggesting Mercury's history is unlike any of the other planets in the solar system. These giant scarps are believed to have formed when Mercury's interior cooled and the planet contracted slightly, causing surface rocks to fracture and some blocks of crust to thrust over others along great faults.
      Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington







  • Noteworthy
    • The middle section of the  ceramic-fabric sunshade is attached to MESSENGER.
        The middle section of the ceramic-fabric sunshade is attached to MESSENGER. The shade, made from the same materials that protect sections of the space shuttle and International Space Station, keeps the instruments at room temperature while the spacecraft orbits the planet closest to the Sun.
      Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

      Orbiting Mercury presents formidable technical obstacles.  A spacecraft has to withstand searing sunlight and roasting heat reflecting back from the planet.  It must be lightweight, since most of its mass is fuel to fire the rockets and slow it enough to be captured by Mercury's gravity.  MESSENGER conquered these challenges with a ceramic-fabric sunshade, heat radiators, and limiting the time spent over the planet's hottest regions.  While temperatures in front of the shade could reach 700° F, behind it the spacecraft will operate at a comfortable 70° F. 

      The MESSENGER team received the National Space Club's Nelson P. Jackson Aerospace Award in April 2009, recognizing exceptional teamwork between government and industry in the missile, aircraft, and space fields.  The MESSENGER mission is a successful collaboration among scientists, engineers, and managers from academia, industry, and NASA.