A crater is simple, right? Well, not really, they are not just holes in the ground (well they are really but they do differ depending on the size of the crater). Once we have become experts on the different types of craters and why they are classified differently then I’ll go through the different ways of spotting a crater.
- The way those intelligent scientists classify craters depends on-
- The size of the thing hitting the surface.
- The speed of the thing (I’ll call that impactor to sound intelligent).
- The things that the impactor are made up of.
- The composition of the rock that is being impacted (the target rock).
- The angle that the impactor hits the surface.
- The gravity of the target planet.
- How porous or strong the impactor is.
Microcraters
Working from the smallest to the largest, microcraters can be as small as no 0.0000001 metres in diameter. These are made by hypervelocity (over 3000 m/s and allows metals to behave like a liquid).
Simple craters are next up on the scale and are a bit more of a serious beast. Meteor crater in Arizona is a typical example of a simple crater. A simple crater is up to several kilometres in diameter and has no central uplift and no terracing. Generally, if you wanna get slightly technical the rim to the floor depth is 1/5 of the diameter.
Simple crater
Complex craters
On the moon it is a bit of a different story as the moon has only has one sixth of the Earth’s gravity. Therefore a larger asteroid or comet is needed to reduce a complex crater with the correct characteristics. The size that is needed is 10 km to about 20 km. If you saw one of these coming towards you on the Earth it would be a good idea to put your head between your legs and kiss …
On Mercury the gravity is one third that of the Earth’s so smaller asteroids or comets are needed to create the characteristics of a complex crater. The impactor needed tends to be around 7 km in diameter.
complex crater
Elongate craters
These are special type of crater that depends on the angle of the impact of the asteroid or comet with the surface. Most impact craters are circular as described in my previous post but at 10° to the surface the impactor tends to glance off and cause a crater that is elongated. The objects that produce elongated craters aren’t small and tend to be bigger than you would think.
elongate crater
These are some of the biggest craters that are found in the solar system. They are produced by the impactor hitting the hard, rigid surface and causing ripples in the layer beneath the surface (the asthenosphere). The asthenosphere is plasticky and viscous and moves in response to the impact. The layer above the asthenosphere, the lithosphere, ripples but is much firmer and rigid and therefore cracks form. These cracks form in circles around the impact.
multiring basin
That’s all the different types of craters that you may come across in the solar system. Outside of the solar system, who knows? It would be nice to spot some of these craters with your telescope or binoculars or even your eyes. On the Earth craters are hard to spot because of erosion and weathering but it is possible although in some cases you have to have quite an imagination.
Poor a list of all the craters on earth that is regularly updated you might like to try the impact cratering database.
- Planar fractures in quartz
- Shocked quartz
- Glass fragments
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“street cred in the, err, crater geek world.” – wow, maybe I can use the info to pick up a cutie with glasses and a white lab coat! But seriously, thanks for the interesting article.
That does sound a little appealing actually …
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