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Today's feature is the 748-nm filter image from from the October 21, 2013 color presentation. The graphs underneath the image illustrate a basic principle of image processing: the contrast stretch. A computer is typically capable of displaying a black and white ("greyscale") image as a series of pixels with 256 levels of brightness, between 0 (black) and 255 (white). Therefore, in order to be displayed, the numerical values of the image must be "stretched" to cover the range 0 to 255. In the case of a calibrated MDIS image, the image values are in physical units of reflectance -- that is, the percentage of incident light that the surface reflects. The graphs underneath the image are histograms. The x-axis is the range of pixel values that occur in the image, and the y-axis is the frequency of the values. The histogram on the lower left shows that the range of reflectance values in the image is from about 0.02 to 0.07 (or about 2% to 7% reflectance). The plot peaks at about 0.04, indicating that the most frequent pixel value is about 0.04. The plot on the lower right shows how the input pixel values have been scaled from 0 to 255 to produce the image above. Note that to display a color image (i.e., in red-green-blue), each of the three input color planes is stretched separately.
This image was acquired as a high-resolution targeted color observation. Targeted color observations are images of a small area on Mercury's surface at resolutions higher than the 1-kilometer/pixel 8-color base map. During MESSENGER's one-year primary mission, hundreds of targeted color observations were obtained. During MESSENGER's extended mission, high-resolution targeted color observations are more rare, as the 3-color base map covered Mercury's northern hemisphere with the highest-resolution color images that are possible.
Date acquired: October 21, 2012
Image Mission Elapsed Time (MET): 259266840
Image ID: 2803280
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -23.00°
Center Longitude: 268.4° E
Resolution: 674 meters/pixel
Scale: The scene is about 890 km (553 mi.) across
Incidence Angle: 45.6°
Emission Angle: 33.5°
Phase Angle: 78.7°
North is up in this image.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This color view of the vicinity of Matisse crater, seen in an early Gallery image from MESSENGER's first flyby of Mercury in 2008. Two unnamed craters formed tangentially to the rim of Matisse (one just inside the rim, and one just outside). These craters have bright orange deposits on their floors. High reflectance and a greater-than-average ("red") spectral slope create the orange appearance in this color presentation. Such color characteristics are found at many other locations on Mercury where pyroclastic volcanic eruptions took place.
This image was acquired as a high-resolution targeted color observation. Targeted color observations are images of a small area on Mercury's surface at resolutions higher than the 1-kilometer/pixel 8-color base map. During MESSENGER's one-year primary mission, hundreds of targeted color observations were obtained. During MESSENGER's extended mission, high-resolution targeted color observations are more rare, as the 3-color base map covered Mercury's northern hemisphere with the highest-resolution color images that are possible.
Date acquired: October 21, 2012
Image Mission Elapsed Time (MET): 259266820, 259266840, 259266824
Image ID: 2803275, 2803280, 2803276
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filters: 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue
Center Latitude: -23.00°
Center Longitude: 268.4° E
Resolution: 674 meters/pixel
Scale: The scene is about 890 km (553 mi.) across; Matisse crater is about 186 km (116 mi.) in diameter
Incidence Angle: 45.6°
Emission Angle: 33.5°
Phase Angle: 78.7°
North is up in this image.
Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
When MESSENGER first flew by Mercury on January 14, 2008, MDIS acquired images of a large portion of Mercury's surface that had never previously been seen by spacecraft. This mosaic of NAC images shows some of the geologic features discovered during that first flyby that have been subsequently named: the curving cliff face of Beagle Rupes, the elongated crater Sveinsdottir, and the craters Izquierdo and Kunisada flooded with lava.
This year, the MESSENGER spacecraft is positioned once again to visit the Solar System's innermost planet. However, this time, the spacecraft won't just pass by. On March 18, 2011, a 15-minute maneuver will place MESSENGER in orbit about Mercury, making it the first spacecraft ever to do so. The MESSENGER mission will then begin an extensive year-long science campaign to unravel Mercury's mysteries. 2011 promises to be an exciting year of further discoveries for the MESSENGER mission.
Date Acquired: January 14, 2008
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: Izquierdo Crater is 170 kilometers (106 miles) in diameter.
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