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Occator and Kirnis craters

Occator and Kirnis craters
Occator and Kirnis craters Dawn had this view on June 24, 2015, from its second mapping orbit at an altitude of 2,700 miles (4,400 kilometers). The scene displays quite a variety of geological features. Most salient is Occator Crater, with its deposits of sodium carbonate and other salts shining in reflected sunlight, at upper left (although you probably didn’t need that helpful guidance in order to find it.) Occator is 57 miles (92 kilometers) in diameter. It is the youngest major feature here. The largest crater, to the right and slightly below Occator, is Kirnis. (Kirnis was a Lithuanian god of cherries. It isn’t known whether he collaborated with deities of chocolate or of sundaes.) This 71-mile (115-kilometer) crater is old, as shown by its degraded appearance, gradually worn down by the particles large and small that fall from space. (Kirnis is too small to have been affected much by the movement of the crust that erases craters.) Notice how the crater rim seems to consist of straight segments. That is most evident for the lower rim, where there is a clear overlap with one of the long linear structures in the right half of the picture. When an impact occurs in an area with fractures, the resulting crater may be shaped by them, yielding a similar polygonal structure, even if there is no other evidence of those fractures visible on the ground. We saw that with Kerwan as well. The fractures in this picture are collectively known as Samhain Catenae. (Samhain, meaning "summer’s end," is a Celtic agricultural festival marking the end of summer and beginning of winter. Halloween can trace its origins to Samhain.) A catena is usually a chain of craters (and is a Latin word for chain), but the term also is applied more generally to large grooves that can be formed by a variety of geological processes. Scientists have not yet determined the mechanism responsible for Samhain Catenae. We will see another catena below. Lociyo Crater, well below Occator, is 21 miles (34 kilometers) across. (Although he was the god of lightning, Lociyo is fortunate to qualify for the naming convention for Cerean craters, because he was associated with agriculture. When the Zapotecs, in what is now Oaxaca, Mexico, cut the first chili of the harvest, they would sacrifice it to Lociyo.) The impact that excavated Lociyo obliterated half of an older crater of about the same size. This scene is centered on this map at 2°N, 249°E. Full image and caption. NASA / JPL-Caltech / UCLA / MPS / DLR / IDA