While the telescopic and Spacecraft observations have provided treasure trove of information on the Surface features and Atmospheres of Planets and Satellites, the geophysical processes involved in the formation of craters, crater lets and ridges are still remaining a tangential question. The two most important processes of Crater Formation that are debated are – 1) Igneous and Volcanic Origin 2) Exogenous Impact.
A dogmatic assertion towards Impact Craters exists despite the irrefutable morphological evidences to the contrary. Many Lunar Craters have volcanic fumaroles and vents. The bright rays from these Craters are gas blown deposits from these vents and crater lets. Further, the forces attributed to Impact cannot act so extensively and so uniformly as to cause these circular structures on a large spherical surface with differential crustal hardness. The Lunar craters show the lava flooding on its surface. Such flooding events seem to arise from the central peak. It is evident from the Lunar Orbiter 2 photographs that the bottom most layers have spread farther distances with successive layers progressively on smaller areas. This causes folding of the upper layers.
On examining the Earth-Moon geometry, it is ratified that any exogenous body must first overcome the Gravity of Earth before impacting the surface of the satellite. This is the case in most of the Planet-Facing Satellites. There is a high probability that the exogenous body is pulled towards Earth’s Gravity and burnt in its Atmosphere. It has also been suggested that the primordial Atmospheres of Planets and Satellites were very dense and hence any object entering the satellite would be obliterated by its Atmosphere. This would either cause a soft landing or less impact due to negligible mass of the impacting material. Earth’s moon had a dense Atmosphere in its past. But it lost its Atmosphere to space due to less Gravity.
The surface topography of Mars (Hellas Basin), Venus (Franklin Crater), Callisto (Valhalla Basin), Galileo crater in Ganymede, Tyco crater in Lunar Surface and many other calderas are also attributed to Igneous and Geophysical origin rather than Impact processes.
Thus, the Author concludes that the impact events do occur in Solar System. But, a preconceived idea of Impact craters for all circular basins cannot be accepted. Also, no morphological impact evidences like impact splashes or regolith melting have been found in the surrounding areas. All these factors drive home the message that most of the Planetary Craters are endogenous in Nature.
I would be happy to find some debatable and controversial theories from my Readers in the comments page.
