Moon, a perfect target for stargazers to start the night with the telescope. But while watching with the telescope we discern that the Moon surface is irregular in shape with small to large circular (bowl-shaped) depressions called craters rather than what we perceive through our naked eyes.
How were craters formed?
Craters were formed when meteors, asteroids, or comets collided with the lunar surface millions of years ago, during the early stages of solar system formation. The size of a crater depends on the size and velocity of the impacting body. The impacts were so powerful that it pulverized the ground creating what we call regolith- and the lines extending from these craters are ‘ejecta rays’ made from the material blasted out of the surface.
Not only there are Moon craters, but there are Earth craters too. But we only know around 170-180 Earth craters, whereas the Moon has more than thousands of craters. Since the geographic processes (like wind, rain, & tectonics movements) that envelop the impact structures here on Earth, don’t occur on the lunar landscape. The Moon once had plenteous volcanic flows in the past that did cover up many of the bigger earlier impacts, but it has been without volcanic activity for around three billion years thereby preserving years of impact history and impact structures. Want to know more about Impact craters? Check out Crash! 10 Biggest Impact Craters on Earth
Types of Lunar Craters:
Lunar craters have a wide array of morphologies. Scientists have used size and form to group lunar craters into three basic categories: Simple craters, Complex craters, and Multi-ringed basins.
This type of crater usually has circular, bowl-shaped structures with smooth to ragged raised rims surrounded by a blanket of ejecta rays. They are usually less than 10 KM in diameter.
These craters have a size larger than 12-20 KM in diameter and often have a rim with one or more terraces. They also have a peak in the center and this peak is brought up from great depths beneath the crater as the ground elastically rebounds after the impact.
The Multi-ringed basins are the largest form of the impact structure. They usually have more than one rim; such as the 1100 KM diameter Imbrium basin.
Some craters possess characteristics outside of these basic categories. Elliptical, concentric, and polygonal are the further classifications for craters on the Moon. Elliptical craters form when the impactor body hits the surface at an angle of 10° or less than 10°. Concentric craters have a basic crater and rim, but they also have perfectly sculpted concentric doughnut-shaped ridge within the crater (called concentric ridge), which makes them unique from other craters.
Enjoyed reading this article? Consider reading Our Moon: Top 5 Interesting Facts that you did not know about