On March 17, 2012, MESSENGER successfully wrapped up a year-long campaign to perform the first complete reconnaissance of the geochemistry, geophysics, geologic history, atmosphere, magnetosphere, and plasma environment of the solar system's innermost planet. The following day, March 18, 2012, marked the official start of an extended phase designed to build upon those discoveries.

What MESSENGER has accomplished since its launch in August 2004 is "amazing," says MESSENGER Mission Systems Engineer Eric Finnegan, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

"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," he begins, checking off the list of mission accomplishments. All this "achieved with a 1,000 kg satellite, designed, built, and launched in less than four years for a total mission cost of less than $450 million."

"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," he continues.

"Before selection many said that the MESSENGER mission to inject a spacecraft into orbit around Mercury and map, in-detail, the surface and surrounding environment could not be achieved within the constricts of NASA's Discovery program. The APL team did it!"

MESSENGER's three flybys of Mercury solved the decades-old question of whether there are volcanic deposits on the planet's surface. But the detailed character and global distribution of volcanic materials remained poorly known until the arrival of MESSENGER in orbit about Mercury.

MESSENGER orbital images have revealed volcanic vents measuring up to 25 kilometers (15.5 miles) across that appear to have once been sources for large volumes of very hot lava that, after eruption, carved valleys and created teardrop-shaped ridges in the underlying terrain.

Also noteworthy is the discovery from measurements of Mercury's gravity field that the planet has an unexpectedly complex internal structure, a finding that will be discussed in a paper to be published by Science Express on March 21, 2012, and at a press conference at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas.

"The last year has been a busy and rewarding one for the MESSENGER project," says MESSENGER Project Manager Peter Bedini, of APL in Laurel, Md.

"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 new MOI animation and a counterpart from March 2011 may be viewed near the end of the animations listed here.