The first image acquired by MESSENGER from orbit around Mercury was actually part of an eight-image sequence, for which images were acquired through eight of the WAC’s eleven filters. Here we see a color version of that first imaged terrain; in this view the images obtained through the filters with central wavelengths of 1000 nm, 750 nm, and 430 nm are displayed in red, green, and blue, respectively. One of MESSENGER’s measurement objectives is to create an eight-color global base map at a resolution of 1 km/pixel (0.6 miles/pixel) to help understand the variations of composition across Mercury’s surface.

This is the first image of Mercury taken from orbit with MESSENGER’s Narrow Angle Camera (NAC). MESSENGER’s camera system, the Mercury Dual Imaging System (MDIS), has two cameras: the Narrow Angle Camera and the Wide Angle Camera (WAC). Comparison of this image with MESSENGER’s first WAC image of the same region shows the substantial difference between the fields of view of the two cameras. At 1.5°, the field of view of the NAC is seven times smaller than the 10.5° field of view of the WAC.

This image was taken using MDIS’s pivot. MDIS is mounted on a pivoting platform and is the only instrument in MESSENGER’s payload capable of movement independent of the spacecraft. The other instruments are fixed in place, and most point down the spacecraft’s boresight at all times, relying solely on the guidance and control system for pointing. The 90° range of motion of the pivot gives MDIS a much-needed extra degree of freedom, allowing MDIS to image the planet’s surface at times when spacecraft geometry would normally prevent it from doing so. The pivot also gives MDIS additional imaging opportunities by allowing it to view more of the surface than that at which the boresight-aligned instruments are pointed at any given time.

The crater near the bottom of this image is a beautiful example of a relatively small, simple, fresh impact feature on Mercury. It illustrates the textbook characteristics of a crater in its size range. The crater is nearly bowl-shaped, with just a small flat area in the center of its floor. The walls and rim are sharp and do not appear to have suffered the collapse and terracing that modify larger craters. The bright ejecta and rays are symmetrically distributed around the crater, indicating that the body that struck Mercury to form the crater approached on a path that was not highly inclined from the vertical.

As the MESSENGER spacecraft passed low over Mercury's north polar region, MDIS used its pivot to capture this image, showing terrain that had not been previously seen by spacecraft. The newly imaged surface is located in Mercury's north polar region, to the north of the bright, rayed crater Hokusai. Looking from the bottom of the image toward the top is looking southward, just as MDIS was doing when this image was acquired.

This newly seen terrain shows craters with long shadows, as expected at this high northern latitude. Understanding the interiors of the craters in Mercury's polar regions and any ices they may contain is one of the main science goals of the MESSENGER mission. The long shadows also accentuate the topography of the surface, which includes a number of ridges that resemble those seen on the expansive smooth plains imaged during Mercury flyby 3.

MESSENGER acquired this image of Mercury's horizon as the spacecraft was moving northward along the first orbit during which MDIS was turned on. Bright rays from Hokusai can be seen running north to south in the image. MDIS frequently acquired images that contained Mercury's horizon during the mission's three Mercury flybys. (Visit these links to see examples of horizon images from Mercury flyby 1, Mercury flyby 2, and Mercury flyby 3.) However, now that MESSENGER is in orbit about Mercury, views of Mercury's horizon in the images will be much less common. The field of view for MDIS will generally be filled with Mercury's surface as the instrument maps out the planet's geology in high resolution, stereo, and color. Occasionally, in order to obtain images of a certain portion of Mercury's surface, the horizon will also be visible.

The wide-angle camera (WAC) is not a typical color camera. It can image in 11 colors, ranging from 430 to 1020 nm wavelength (visible through near-infrared). It does this with a filter wheel: the 11 narrow-band filters (plus one clear filter) are mounted onto a wheel that can be rotated to allow the camera to capture an image through each filter. In this image the 1000 nm, 750 nm, and 430 nm filters are displayed in red, green, and blue, respectively. Several craters appear to have excavated compositionally distinct low-reflectance (brown-blue in this color scheme) material, and the bright rays of Hokusai crater to the north cross the image. During MESSENGER’s orbital operations, we will typically use just eight of the WAC's filters. This decision was made to reduce the amount of data that must be stored on the spacecraft’s solid-state recorder before the information can be downlinked. It’s also quicker than cycling through all 11 filters – the spacecraft is moving rapidly over the surface, and there isn't much time to image the same spot on the surface 11 times over before moving to the next area of interest. The sets of color images will help us learn about the variation in composition from place to place on the planet. For example, some minerals such as olivine and pyroxene often absorb more light at longer wavelengths than at shorter ones, so we’ll be looking for their signatures in the reflectance spectra derived from each eight-color set. WAC images will be used in coordination with the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), a hyperspectral instrument that provides reflectance information at many more wavelengths, but only for one spot on the surface at a time.

This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of ~450 km (280 miles) above the planet during the spacecraft’s first orbit with the camera in operation. The area is covered in secondary craters made by an impact outside of the field of view. Some of the secondary craters are oriented in chain-like formations.

This image was taken during MESSENGER’s closest approach to the sunlit portion of the surface during this orbit, just before crossing over the terminator. The oblique illumination by the Sun causes the long shadows and accentuates topography. The highly elliptical orbit of MESSENGER brings the spacecraft down to a periapsis (MESSENGER’s closest approach to Mercury) altitude of ~200 km (125 miles) and out to an apoapsis (MESSENGER’s farthest distance from Mercury) altitude of ~15,000 km (9300 miles).

Bright rays, consisting of impact ejecta and secondary craters, spread across this NAC image and radiate from Debussy crater, located at the top. The image, acquired yesterday during the first orbit for which MDIS was imaging, shows just a small portion of Debussy's large system of rays in greater detail than ever previously seen. Images acquired during MESSENGER's second Mercury flyby showed that Debussy's rays extend for hundreds of kilometers across Mercury's surface. Debussy crater was named in March 2010, in honor of the French composer Claude Debussy (1862-1918).

Early this morning, at 5:20 am EDT, MESSENGER captured this historic image of Mercury. This image is the first ever obtained from a spacecraft in orbit about the Solar System's innermost planet. Over the subsequent six hours, MESSENGER acquired an additional 363 images before downlinking some of the data to Earth. The MESSENGER team is currently looking over the newly returned data, which are still continuing to come down. Tomorrow, March 30, at 2 pm EDT, attend the NASA media telecon to view more images from MESSENGER's first look at Mercury from orbit.

This historic first orbital image of Mercury was acquired 37 years to the day after Mariner 10’s historic first flyby of the innermost planet. Labels have been added to indicate several craters that were named based on Mariner 10 images, as well as Debussy, Matabei, and Berkel, which were named based on MESSENGER flyby images. The surface contained in the white lines is terrain previously unseen by spacecraft, and the star indicates the location of the south pole.