MESSENGER

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 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.

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. 

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.

	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.