Messenger Completes Mercury Mission
March 21, 2012

Messenger Completes Mercury Mission, Enters Extended Phase

In Roman mythology Mercury was the “Messenger of the Gods,” — as well as a god of trade, thieves and travel. It is thus fitting — apart from the trade and thieves aspect — that the MESSENGER program has been so carefully studying the inner most planet in our solar system.

MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) this week successfully completed a year-long mission to perform the first complete reconnaissance of the geochemistry, geophysics, geologic history, atmosphere, magnetosphere, and plasma environment of the planet Mercury, and now begins an extended phase designed to continue and build upon these discoveries.

"Six plus years of cruise operations, capped by a year of nearly flawless orbital operations, with an additional year of scientific return ahead in the harsh environment at 0.3 astronomical units (27,886,766 miles) from the Sun," said MESSENGER Mission Systems Engineer Eric Finnegan, of the Johns Hopkins University Applied Physics Laboratory (APL) in a statement.

MESSENGER is a 1,000 kg satellite, which was designed, built, and launched in less than four years for a total mission cost of less than $450 million, added Finnegan. “"This is a testament to the hundreds of innovative, talented, and dedicated engineers, technicians, and support personnel here at APL and around the world who contributed to this mission.”

This is the second NASA mission to the inner-most planet. NASA´s Mariner 10 was launched in 1973 to fly by Venus before approaching to Mercury, arriving in 1974 and circling the planet and the sun multiple times before running out of fuel in 1975.

MESSENGER was launched on August 3, 2004 from Cape Canaveral Air Force Station, and made its first fly-by of Mercury on January 14, 2008, followed by a second fly-by in October of 2008 and another in September of 2009. The probe entered an elliptical orbit around the inner-most planet on March 18, 2011 to begin its year-long mission.

On January 12, MESSENGER captured images with the Narrow Angle Camera (NC) that provided a close-up look at the Picasso crater, named for 20th century Spanish painter Pablo Picasso.

The craft´s three flybys of Mercury have reportedly solved a decades-old question about whether there are volcanic deposits on the planet´s surface, and orbital images have revealed volcanic vents, which do appear to have once been sources for large volumes of very hot lava.

Additionally, MESSENGER´s radio tracking has given the scientific team the first opportunity to develop the first precise model of the planet´s gravity field. Combined with the topographic data and the planet´s spin state this had shed light on Mercury´s internal structure, the thickness of the crust and the size and shape of its core, as well as the planet´s tectonic and thermal history. This has allowed the team to learn that the core occupies a large fraction of the planet, about 85 percent of its radius.

The scientists, led by MIT researchers David E. Smith and Maria T. Zuber, further found that Mercury's solid outer core and liquid inner core contain more iron than Earth, relative to the whole planet. This further influences the way Mercury's magnetic field was generated, while Peale also noted that the surface is comprised of lighter elements.

"We didn't expect so much sulfur," Peale said in a statement, and added that there was almost no iron found on the surface of the planet. With no iron, the volcanic surface rocks are too light to have come from a mantle with the large average density derived for the internal structure. This led to the concept of a two-layer mantle —— with a light upper silicate layer, which could provide the low-density surface material —— over a dense iron sulfide layer.

“The last year has been a busy and rewarding one for the MESSENGER project,” said MESSENGER Project Manager Peter Bedini, of APL in Laurel, Md. in a statement. “As the engineering and operations teams closely monitored the spacecraft's response to Mercury´s seasons, the science team was busy analyzing data and filling gaps in our understanding of the planet. Science results from the first year of orbital operations have influenced the observation plan for the second year, which we expect to be as busy as the first, and hope to be as rewarding.”

“The first year of MESSENGER orbital observations has yielded a wonderful harvest of results,” said MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution and a coauthor of the two papers in a statement. “From Mercury's extraordinarily dynamic magnetosphere and exosphere to the unexpectedly volatile-rich composition of its surface and interior, our inner planetary neighbor is now seen to be very different from what we imagined just a few years ago. The number and diversity of new findings being presented this week to the scientific community in these papers and in presentations at this week's Lunar and Planetary Science Conference provide a striking measure of how much we have learned to date.”