Planetary Science

What is the difference between a moon mare and a crater?


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Craters are produced in two ways - the first way is as a result of a volcano- the crater being the caldera of the volcano. On the moon volcanoes are now extinct, but their remains, as craters, can be seen. The second way is by impact. A large object like a meteoroid (it becomes a 'meteorite' when on the surface of the planet), when impacting on the moon, can produce a large pit that we call a crater. On earth any craters formed over the millions of years are eroded away by our atmosphere and weather (although some survive like the 'meteor crater' in the USA)> However, on the moon, where there is no appreciable atmosphere, the craters can last for millions of years with little change. Maria (Mare is singular, Maria - plural)or 'seas' are not seas (although they were once thought of like that - hence the name) but are solidified plains of lava that erupted frrom lunar volcanoes covering large areas of the moon's surface. Dating craters and maria is quite simple; if a crater is formed in one of the maria, then it was made after the mare solidified or the crater would have been desroyed by the molten lava. Occasionally craters form on top of other craters. The latterly formed crater is the one that is clearly superimposed on the older one.