The primary science phase begins April 4 and will last about one year; during that time, Messenger is expected to gather more than 75,000 images.
Messenger approaches MercuryAfter three flybys of Mercury over the last three years, the Messenger spacecraft is poised to settle into the first-ever orbit by a manmade object of the planet closest to the Sun. The goal of the mission is to provide scientists with data on Mercury unparalleled since the Mariner 10 spacecraft passed by three decades ago. And the more we understand about Mercury, NASA says, the more we'll understand about how the other rocky planets in the solar system--Venus, Mars, and of course, Earth--formed and evolved.
The insertion into orbit starts at about 9 p.m. ET on March 17. From that point on, Messenger will fly a 12-hour orbit at a minimum altitude of about 124 miles. The spacecraft's science instruments will be turned on and checked out starting on March 24.
Caloris basinMercury isn't really blue and gold. "In general," says NASA, "in light visible to the human eye, Mercury's surface shows only very subtle color variations." The space agency explains how it gets from subtle to bold: when images from all 11 narrow-band color filters of the Wide Angle Camera in the Mercury Dual Imaging System "are statistically compared and contrasted, these subtle color variations can be greatly enhanced, resulting in extremely colorful representations of Mercury's surface."
In this mosaic of what NASA calls the "eastern limb" of Mercury, from the January 2008 flyby (the first of the three by Messenger), the large gold-hued circular area is the Caloris basin, notable for its volcanic plains. The basin is about 960 miles in diameter, and Messenger was passing by at a distance of about 8,000 miles.
October 2008 flybyThis enhanced-color mosaic comes from the second flyby of Mercury, which took place in October 2008, as Messenger was flying away from the planet--hence the widening in the series of images. The narrowest images, at left, were taken about nine minutes after the spacecraft's nearest approach, while the widest were take at the 15-minute mark, when Messenger was twice the distance away. The small blue crater at upper right (a "young, rayed crater"--the rays fade over time with exposure to the harsh space environment) has since been named Dominici. Click here for a larger view of the mosaic.
The name "Messenger," by the way, stands for a much longer phrase: MErcury Surface, Space ENvironment, GEochemistry, and Ranging.
Orbiting MercuryThis graphic shows two views of Messenger's orbit, one from the perspective of Earth, the other from the perspective of the sun. At least once every Mercury year (about 88 Earth days), the spacecraft will have to execute "propulsive maneuvers" to keep its minimum altitude below 310 miles. After entering orbit this week, Messenger will have just 9.5 percent of the usable propellant it carried when it left Earth in August 2004, but that will be plenty for the orbital corrections it will need to make, NASA says.
The diameter of Mercury is 3,030 miles.