Mercury's Caloris Basin Is Buried In Kilometers Of Lava

Once upon a time, the Caloris basin on Mercury was flooded with lava, forming a volcanic layer 2.5 to 3.5 kilometers thick with an occasional fresh crater punching through to the original basin floor.

The image is enhanced-colour, revealing geological details. As NASA explains:

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.).

A Color-Saturated Look At Mercury's Massive, Ancient Caloris Basin

Mercury's Caloris Basin is seen in an enhanced color mosaic. The massive crater, formed some 4 billion years ago, is orange. Smaller craters made subsequently are rendered in blue, while orange splotches around the perimeter may be volcanic vents.

(Side note: Props to the punster who titled the photo "All About that Basin" on the Jet Propulsion Laboratory's Photojournal page.)

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington