On May 3, MESSENGER's Mercury Dual Imaging System delivered the 100,000th image of Mercury since the spacecraft entered into orbit around the planet on March 18, 2011. The instrument — one of seven aboard the spacecraft — has globally mapped the planet in high-resolution monochrome images and in color images through eight of its color filters, uncovering a new view of Mercury and shedding light on the planet's geologic history.
"That our inventory of orbital images of Mercury is now expressed in six figures constitutes an important footnote in the history of solar system exploration," offers MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "The MESSENGER mission has at last provided us a view of the innermost planet that is fully global, multispectral, and at a range of illumination conditions. Moreover, we are steadily building a library of targeted high-resolution images that allow us to view features and discern geological processes in unprecedented detail."
This image is a portion of the MDIS global mosaic basemap showing a region of smooth, volcanic plains that have been heavily modified by tectonic structures termed "wrinkle ridges."
Because of Mercury's proximity to the Sun and its slow rotation, designing an imaging system for an orbital mission presented quite a challenge, says MDIS Instrument Engineer Ed Hawkins of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD.
"The sunshade protects the spacecraft from direct solar illumination, but we knew it would constrain a camera's range of pointing," Hawkins says. "So, we had to come up with a system that would be able to capture the required observations of the planet, maintain the thermal safety requirements and not jeopardize the safety of the spacecraft.
"We finally came up with the idea for a pivoting mechanism that gave the instrument an extra degree of freedom, allowing it to obtain extra observations even when the spacecraft — and the rest of the instruments — were facing away from the planet."
The system has exceeded the team's expectations, he says. "We obtained images of Earth and Venus, but those were primarily to test the instrument. We used fairly simple spacecraft pointing options and exercised basic MDIS exposure control and compression options," he says. But the instrument's performance during the first flyby of Mercury in January 2008 was the first demonstration of the instrument's full capabilities.
"When we received that first image after the first flyby, it confirmed for us that the imaging system we designed was working, and since then the camera has been operating flawlessly," he says.
The 100,000 images from Mercury's orbit constitute an important milestone, says MDIS Instrument Scientist Nancy Chabot, of APL. But there is still much more to come. New images are returned from Mercury orbit on nearly a daily basis, and scientists around the world are studying these images to decipher Mercury's history and evolution.
Track the MESSENGER mission as MDIS begins to acquire the next 100,000 images from Mercury orbit by going online or downloading the MESSENGER app.