Why does the moon have craters?
Our Moon’s surface is pock-marked with craters formed by collisions from meteorites, comets, and asteroids. The average speed of an asteroid striking the Moon is about 12 miles per second. When one of these visitors strikes the solid surface of the Moon, the resulting shock wave fractures the rock and digs a cavity, or bowl shaped hole, about 10 to 20 times the diameter of the impacting rock.
The colliding asteroid is shattered into smaller pieces that may either melt or vaporize. The Earth has many craters formed by the collision from asteroids and meteorites. But the Earth has a thick atmosphere that acts as a shield.
As soon as an asteroid comes in contract with our atmosphere, the air in front of the asteroid packs together, increasing the temperature to thousands of degrees. The meteorite catches fire. We see it as a shooting star or falling star.
Most of these meteorites disintegrate before they have a chance to reach the surface of the Earth. Our atmosphere acts as a safety shield and a cushion to protect the surface we live on. The Moon has no such protecting atmosphere. It is estimated that the Moon is hit with over a ton of meteorites every day.
The Moon has been beat up really bad. The surface of the Moon reveals the evidence of millions of years of bombardment. Copernicus is a large crater that is 60 miles across. The impact craters on Earth have been eroded away by plate tectonics, wind, rain, glaciers, and surface changes. Geologic processes have not erased the Moon craters over billions of year.
The Earth actually has more impact craters than the Moon. The Earth is four times the diameter of the moon. It presents a bigger target for wayward asteroids and comets.
All the solid bodies of the solar system exhibit impact craters. Mercury looks much like the Moon. Venus is covered with thick carbon dioxide clouds, but remote robotic landers show the surface to be heavily cratered. Venus and Mars have had volcanic activity that filled in the craters.
There are 57 known impact craters in North America alone, with over 170 spread over the Earth. The Chicxulub crater in the Yucatan peninsula of Mexico is not easily seen, but satellite images, changes in the gravity field, and ringlike structures give clues to its size. The resulting fires, tsunamis, and clouds of dust and water vapor are believed to have led to the extinction of dinosaurs 65 million years ago.
The oldest and largest impact crater recognized on Earth is the Vredefort crater in South Africa. It is two billion years old and 185 miles across.
A visit the Barringer Crater near Winslow, Arizona must be put on your bucket list. A 160 foot wide iron-rich meteoroid struck there 50,000 years ago. It left a crater about a half mile wide and 650 feet deep. They have a beautifully constructed visitor center, extensive displays, and guided tours. You can walk down into the crater or all the way around it if so inclined.
In 1908, a large meteoroid or comet hit in Siberia, Russia near the Tunguska River. This Tunguska event was a powerful explosion equivalent to 1,000 A-bombs dropped on Hiroshima, Japan in 1945. The blast knocked over 80 million trees killed a lot of reindeer.
Recently, on February 16, 2013, a 55 foot wide rock lit up the skies over Ural region of Russia. It was traveling at 44,000 miles per hour. It broke up at 15 miles above the earth’s surface. The shockwave injured 1,200 people.