Why Does the Moon Have Craters?

The surface of the moon is heavily indented with craters, which are believed to be formed by collisions from asteroids, comets and meteorites.These asteroids and meteorites that collide with the surface of the moon travel at an average speed of about 20 kilometers per second, creating large bowl-shaped holes on the surface known as impact craters. When a small meteor travelling at such high velocity hits the surface, the resulting crater will actually be 10 to 20 times more in diameter, compared to the colliding meteorite.

The earth too has craters formed by collision from asteroids and meteorites but to a far less extent in comparison to the moon. This is because the earth has a thick atmosphere that protects it from possible asteroid collisions.

The atmosphere of the earth is over 560 kilometers thick and as soon as the asteroid comes into contact with the atmosphere, the air molecules in front of it pack together, causing its temperature to rise rapidly to intense levels. These high temperatures of up to over 1,500o Celsius cause the meteorite to catch fire and combust. These can be observed as ‘shooting stars.’ Most meteorites disintegrate before they get a chance to reach the earth’s surface. The ones that do make it may be too small to cause any impact. The earth’s atmosphere acts as a cushion to protect the surface from meteor impacts.

Besides, while the craters on the earth may come from sources such as rock fragments ejected from volcanic activities, the craters on the moon are almost entirely attributable to asteroid collisions.

To sum up, the 2 widely accepted answers given for the question “Why does the moon have craters?” are:

1. The Moon does not have an atmosphere to shield its surface from meteorites, unlike the earth whose thick atmosphere burns up meteorites combusting them to nothingness before they reach the surface.

2. Unlike the earth, whose surface is constantly shifting and evolving due to plate tectonics, the surface of the moon is inactive. This means most of the impact craters that were on earth have been eroded away by the elements while the craters on the moon have been unaffected by such elements.

For a long time now, the moon has been considered to be surrounded by a vacuum with no atmosphere. But recent studies show that the moon does have an atmosphere – albeit a very thin one, in comparison to the earth. Most of the moon’s atmosphere is brought about by a phenomenon called outgassing. Outgassing is where gasses such as helium, radon and even water vapor are released from the moon’s mantle and crust. Even then, the moon’s fragile atmosphere is only 100 trillionth of earth’s atmosphere, a very thin band, detectable in certain places more than others. The moon’s tenuous atmosphere does not help shield it from asteroids, unlike the earth’s.

Considering that the moon has a significantly smaller surface area compared to the earth, it would be an exaggeration to say that the moon protects earth from some asteroid collisions.

In fact, Jupiter is considered to be ‘Earth’s Shield’ deflecting many calamitous asteroids that would otherwise bombard earth and cause large-scale extinctions, not unlike the sudden extermination of dinosaurs. Jupiter hurls arriving asteroid bodies away by the sheer force of its gravity. However new studies say that as much as the gas giant deflects asteroids, it also flings them into the solar system, making it a possible nuisance rather than a protector.

Astronomers still haven’t found out the exact number of asteroids that hit the moon on a daily basis. However, a NASA study led by Bill Cooke, the head of NASA's Meteoroid Environment Office in Huntsville, AL noted that “every day more than a metric ton of meteorites hit the moon.” The numerous craters that we see on the moon now could be products of over billion years of collision activity.

Surprisingly, majority of the lunar craters are much shallower than you’d think. The only known exception is South Pole Atkins Basin whose dimensions measure 2000 kilometers by width and 13 kilometers by depth.

Could it be that the craters in the moon are shallow because of the strong material that the moon is made out of? The composition of moon is said to have elements such as iron and titanium. Titanium is an extremely hard metal that is used to construct the exterior of airplanes and ships. Perhaps the hardness of the moon’s surface makes it difficult for meteorites to penetrate deeper…

Most of the craters on the moon are simple bowl-shaped and circular craters that have a diameter of less than 15 kilometers. But some craters on the moon do not have a circular shape. Featured in the picture to the right are two craters in the Mare Fecunditatis region of the moon which are not circular. The shape of the craters Messier and Messier A is puzzling and scientists have yet to find out the exact reason for their shape.

The oldest craters on the moon have been measured to be around 2 billion years old.

Astoundingly, the oldest rocks sampled from the moon’s outer crust have been found to be over 5 billion years old yet the oldest impact crater is only 2 billion years old. This leaves a good 3 billion years of the ancient moon just laying there without any impact from asteroids. Yet, while the solar planetary system was still developing, it was a harsh environment with maniac asteroids whizzing around in frenzy ready to strike any surface whose gravity could alter its course. It is important to note that although NASA has technology to accurately estimate the age of the moon, no clear estimate is given, with numerous other reports stating the moon to be older than the earth. Some reports say the moon is over 20 billion years old yet the earth is only 4.6 billion years old. These claims are subject to dispute, but if all falsehood is based on truth, is there an element of truth in saying the moon is older than the earth?

Mysterious Moon

The moon, earth’s closest companion for as long as we can remember, is wrapped in enigma. There is more to the moon than meets the eye. How many secrets does the moon hold? Is the moon really older than the earth and the sun? Is it really a foreign addition to the solar system? If so, who placed it there?