Another Crater from last 3rd April. As an Eastern entertainment, I am trying to find/learn as much as possible from the features in the resulting images. In revision G I have higlighted some of them.

Please, bear in mind that all the text that follows is not originally from me but a "patchwork" of several sources (being the one most used The Cambridge Photographic Moon Atlas from Alan Chu & Cambridge University Press, which I am enjoying a lot and certainly recommend it!). I have put them together for fun and "self education".

Copernicus

Copernicus is the perfect example of a large complex crater, with its diameter of just 96 km. Its inner ramparts are in the form of terraces, the crater floor is flat, smooth, and largely covered in flat hills. The central mountain range is complex, with numerous peaks. Instead, the inner walls of the crater sag under their own weight into multiple annular terraces making up a series of steps. The pressure and temperature possibly caused the rocks at the impact point to behave as a viscous fluid. As such, the material did not slump vertically, but slid over a curved surface towards the centre of the crater. This increased the crater’s internal diameter. The circular rim has a discernible hexagonal form, with a terraced inner wall and a 30 km wide, sloping rampart that descends nearly a kilometer to the surrounding mare. There are three distinct terraces visible, and arc-shaped landslides due to slumping of the inner wall as the crater debris subsided. Copernicus inner crater walls tower 3.7 km above the crater’s floor. A group of central mountains reaches up to heights of 1.2 km above the floor. The height of the outer ramparts amounts to only about 900 m.

Most likely due to its recent formation, the crater floor has not been flooded by lava. The terrain along the bottom is hilly in the southern half while the north is relatively smooth.

The central mountains contain large quantities of olivine, which was actually formed deep beneath the surface of the Moon, but which was brought to the surface by the enormous impact. The radial scratches, furrows and notches around the crater’s rim were caused by ejecta that was melted by the impact, and which are still easy to see because of the crater’s young age. In comparison to similarly large, but significantly older craters in the southern highlands, Copernicus is ‘fresh’, as if it had just been created. Landslides are clearly visible around the eastern inner crater wall, possibly created by shock waves from the much later Tycho impact.

Other Features of interest (see associated revision G)

A large number of smaller secondary craters, crater pits and depressions lie in the terrain to the northeast of Copernicus. They were created by secondary impacts. A bright, extensive and very complex ray system becomes visible around the crater under high solar illumination. Elongated or irregularly shaped craterlets are mainly secondary craters. They occur following an impact, when the impact energy has broken up the crustal material, flung it upwards and explosively hurled it outside the crater. The blocks of rock are generally partially or completely molten and the angle at which they are projected is very flat, which leads to the formation of irregular or elongated craterlets. Impressive examples are the surroundings of Copernicus, and particularly the area around the crater Stadius saturated with secondary craters.

Stadius is a shallow depression with a broken crater wall, 69 km in diameter. The height of the southeastern wall remnant amounts to only about 600 m. The crater is practically completely covered with ejecta from the Copernicus impact and saturated with secondary craters and crater pits.

DMD (DMD is the abbreviation for Dark Mantle Deposit. ) regions are areas of the lunar surface that have been covered in dark volcanic ash, which originates from the mantle, and which may be attributed to strong, eruptive pyroclastic volcanism. DMD regions are the observable remains of vigorous active volcanism in ‘recent’ times, because they largely overlie all earlier changes of the lunar surface that have been caused by impacts and their ejecta. In at least one of the regions (southeast of Copernicus) large instruments reveal lunar domes with summit craters and fractures within a DMD region. The lava rising from deep within the Moon was very fluid and was carrying a large proportion of compressed gas (probably carbon monoxide) under high pressure. When the lava reached the surface through the vent, the gas expanded explosively in fractions of a second and the lava positively exploded, sending it in fountains hundreds of metres – perhaps, being on the Moon, a few kilometres high.The lavas were rich in iron and titanium and were thus darker in colour than most of the lavas that filled the basins. These particles of fluid lava cooled very rapidly, and crystallized into tiny glass-like spheres and ‘rained’ down – together with other ash particles – onto the lunar surface. Because of the Moon’s weak gravity, the lava probably reached great heights above the surface, and the ashes were spread correspondingly widely around the feeder vents and fissures.

The domes are generally circular in form, with a diameter of 6–8 kilometers (4–5 mi), and rising as high as 400 meters (1300 ft). They are formed of the same material as the surrounding mare, although from a different process. Typical examples of lunar mare domes. Mare domes are generally broad, convex semicircular landforms with relatively low topographic relief. The formation of mare domes is thought to be related to eruptions of more viscous and more silicic lava than normal mare basalts, intrusions of shallow laccoliths, or mantling of large blocks of older rocks with younger lavas. These domes probably formed during the later stages of volcanism on the Moon, which is characterized by a decreasing rate of lava extrusion and comparably low temperature eruptions. This eruption style contrasts the emplacement of early stage, high volume, high temperature fluid mare basin deposits. Lunar mare domes, like the Hortensius domes, are distinctly different from non-mare domes like those found in the Gruithuisen region, which have much steeper slopes and higher albedo.