Crater chains are just one type of feature we are looking out for in Moon Zoo but they are proving to be rather elusive. A number of processes can leave a chain of craters (a Catena):
- Boulders from a larger impact are flung out and form smaller secondary craters where they land. The larger the impact the further away the ejected boulders are thrown. In really large impacts ejecta can be hurled hundreds of kilometres away. Some boulders land on their own forming isolated small craters; a group of boulders landing together can form a ridged herringbone pattern and a string of boulders landing together can form a chain of craters which fall radially to their parent crater. Individual craters in the chain are also usually elongate in shape (due to the shallow angle of impact) with irregular rims and the ejecta appears ‘splashed’. Isolated secondary craters are often difficult to identify but craters in chains are easier to spot and can, therefore, be studied as secondary craters.
- The impact of a fragmented meteorite or comet might also have created a crater chain.
- Some crater chains are thought to be volcanic in origin but it can be difficult to distinguish between the two types of crater chains. Volcanic crater chains are lined up along a common fault or set of faults, and each crater produces a blanket of volcanic ejecta. As you would expect, volcanic crater chains are not assocated with a parent crater.
There are many – too many – examples of three or four small craters in a line and while these may well be secondary craters from a larger impact they are not especially noteworthy. Some of the more famous crater chains are very impressive and contain over 20 smaller craters. It would be quite something if we could find an example like that.
These are some of our contenders so far:
Posted by Forum member Caro:
Moon Zoo team member Irene Antonenko says:
“The wispy, feathery texture associated with crater chains is formed when the ejecta deposits of the craters in the chain interfere with each other during their emplacement (kind of like point-source waves interfering in a wave tank.)”
Discussion on the forum concluded that the impact angle was so low that the top part of the impactor sheared off and bounced to form the “tail.”
If you want to read more about Crater Chains try these links:
Finding a good, clean example of a long crater chain, whether volcanic or impact in nature, is this week’s challenge!
Jules is a volunteer moderator for the Moon Zoo Forum.