Craters are the most common surface features on many solid planets and moons—Mercury and our Moon are covered with craters. This portion of the Moon is covered by numerous circular holes. These are impact craters, each of which was formed when an asteroid or comet collided with the Moon's surface.
The large number of craters in this region indicates that this part of the Moon is quite ancient. Geologic processes have not erased the craters with time. What happens when an impactor hits? When an impactor strikes the solid surface of a planet, a shock wave spreads out from the site of the impact.
The shock wave fractures the rock and excavates a large cavity much larger than the impactor. The impact sprays material — ejecta — out in all directions. The impactor is shattered into small pieces and may melt or vaporize. Sometimes the force of the impact is great enough to melt some of the local rock. If an impactor is large enough, some of the material pushed toward the edges of the crater will slump back toward the center and the rock beneath the crater will rebound, or push back up, creating a central peak in the crater.
The edges of these larger craters also may slump, creating terraces that step down into the crater. What are the different kinds of craters? Simple craters are small bowl-shaped, smooth-walled craters the maximum size limit depends on the planet. This image shows a simple crater on Mars that has no central peak or terraces around its edges. The crater is 2 kilometers about 1 mile wide.
An extensive blanket of ejecta covers the area around the rim. Complex craters are large craters with complicated features.
Larger craters can have terraces, central peaks, and multiple rings. Copernicus is a large crater 93 kilometers or 60 miles wide on the Moon. The inner walls of the crater have collapsed to form a series of step-like terraces, and a central peak is visible in the center of the image.
A complex crater in the northern region of Mars. This crater is about 20 kilometers 12 miles across and has a large central peak and terraces around its rim.
The ejecta blanket has lobes, which may indicate wet material was ejected, suggesting that subsurface water or melted ice was mixed into the debris. Impact basins are very large impact structures that are more than kilometers miles in diameter. The largest impact basin on the Moon is kilometers miles in diameter and more than 12 kilometers 7 miles deep. Large impact basins are also found on other planets, including Mars and Mercury.
The large circular dark areas in the image are impact basins, created as huge impactors struck the Moon. Lava later flowed across the low floors of the basins, giving them a darker, smoother appearance than the surrounding, brighter highlands.
The dark basins can be seen by the naked eye. Scientists describe other types of craters as well:. During the first stage, the energy forces the target rocks down and compresses them. A transient crater starts to form-- we call it 'transient' as this early crater will change.
Material is then melted, even vaporized, and starts to be thrown out of the rapidly expanding crater during the excavation stage. For larger impact events, however, this transient crater is unstable-- its basically too deep and wide. Rocks at the bottom of these craters resist being compressed and deformed, and eventually 'snaps back' during the modification stage. This is the process that pushes up the central peak in complex craters.
Finally, the ejecta falls to the ground, and the rim and center of the crater slump a bit and settle into their final shapes. All of this happens within a few minutes, although for larger craters the melted rocks can take a very long time to cool and harden again, and the rim and peaks may fall and slump a bit more.
And then of course Just like people, craters age too. They change with time, given what is going on around them in their environment. On the Moon, where there is no wind, rain, or atmosphere to speak of, craters can remain fresh-looking for quite a while. But even with no Earth-like atmosphere, craters can slowly erode, and eventually more craters form on top of the older, beat up craters.
The Earth is a tough place to be a crater. Once formed, impact craters are immediately subjected to wind, rain, earthquakes, landslides, volcanism, and even plate tectonics. All of these processes act slowly, and not so slowly, to change their original appearance, making them hard to identify. In addition to these natural geologic processes at work, there are biologic ones as well-- craters can be covered by plant life and trampled by animals.
Humans have even built cities over them, never realizing they were there! But how can that be? Something that big ought to be pretty easy to spot, even if its worn down, right? Well, things can look very different on the ground than they do from the air. A nice, fresh, small crater might be easy to identify, even looking at it from an angle, like this one to the left. And at the rim of Meteor Crater, this is something you wouldn't miss, as you saw from the earlier air photo.
But what about much larger craters? They too can be very difficult to identify. You might be standing right next to one and not realize it. Note this lunar crater. This picture was taken from an orbiter, so we are still above the surface. Even so, the crater is difficult to identify. What if we were standing on or near the rim? The image above was taken standing on the surface along the edge of a crater. This is a panoramic view of the Haughton impact structure in Canada.
Can't quite see it? Does anything stand out? Does it look circular at all? Check out a short movie from stop 1 of the Haughton Virtual Tour. Still not sure? Well, as we said, they can be difficult to identify and even scientists have to work hard to see them. And how about the Moon's Smithii Basin to the right?
At more than kilometers across, this is one large impact basin! But that very fact makes it incredibly difficult to recognize from the ground. From inside the crater, you would never be able to see the outer rim-- it would be beyond the horizon. You would never know you were standing in a crater But scientists have identified lots of impact craters on Earth.
The map to the left shows a total of that have been discovered around the world see the Earth Impact Database of the University of New Brunswick. So, if scientists have found this many, they must looking for very specific things to really know that they are impact craters.
Perhaps its time to take a Virtual Tour and find out! All Rights Reserved. Skip to main content. Login Register. You are here Home. These are good questions and they are outlined below: A What is an 'impact event' and what is an 'impact crater'? When two objects collide it is called an impact event The basic idea is simple-- objects in space sometimes run into one another.
This scar is the impact crater In the image below, artist Don Davis has imagined what a very large asteroid impacting Earth might look like. Simple Craters The image to the left is a very simple, bowl shaped crater on the Moon and is typical of small craters that have formed relatively recently.
From the air, as shown above, it looks very much like the simple crater on the Moon. A huge meteorite or asteroid created this giant crater 2. Most of them use items you probably already have in the house. What are you waiting for? Science Sparks Wild Sparks Enterprises Ltd are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources.
Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources. These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.
I love it — the way that the flour comes to the surface really explains how there is difference in the colours of the moon surface. Got to try this out. Your email address will not be published. What is a crater? What you need for a crater experiment A shallow metal pan Plain white flour Drinking chocolate Marbles and different sized balls.
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