English: This mosaic of Caloris basin is an enhanced-color composite overlain on a monochrome mosaic featured in a previous post. The color mosaic is made up of WAC images obtained when both the spacecraft and the Sun were overhead, conditions best for discerning variations in albedo, or brightness. The monochrome mosaic is made up of WAC and NAC images obtained at off-vertical Sun angles (i.e., high incidence angles) and with visible shadows so as to reveal clearly the topographic form of geologic features. The combination of the two datasets allows the correlation of geologic features with their color properties. In portions of the scene, color differences from image to image are apparent. Ongoing calibration efforts by the MESSENGER team strive to minimize these differences.

Caloris basin has been flooded by lavas that appear orange in this mosaic. Post-flooding craters have excavated material from beneath the surface. The larger of these craters have exposed low-reflectance material (blue in this mosaic) from beneath the surface lavas, likely giving a glimpse of the original basin floor material. Analysis of these craters yields an estimate of the thickness of the volcanic layer: 2.5-3.5 km (1.6-2.2 mi.).

• Date published online: November 15, 2014
• Instrument: Mercury Dual Imaging System (MDIS)
• Center Latitude: 31.5°N
• Center Longitude: 162.7°E
• Projection: Orthographic
• Scale: Caloris basin is approximately 1525 km (948 mi.) across
• Reference: Ernst et al. (2015) Stratigraphy of the Caloris basin, Mercury: Implications for volcanic history and basin impact melt, Icarus 250, 413-429.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. During the first two years of orbital operations, MESSENGER acquired over 150,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015.