Messala (crater)
Messala is a large lunar impact crater, 122.40 km in diameter, centered at 39.29°N, 60.07°E on the northeastern nearside of the Moon, close enough to the limb that it appears strongly foreshortened from Earth.1 Because of its size, it would once have been classed as a "walled plain," and it was named by the International Astronomical Union in 1935 after the astronomer Mashaallah ibn Asari, who lived between the 8th and 9th centuries.2 • 3
| Key fact | Detail |
|---|---|
| Diameter | 122.40 km (IAU/USGS Gazetteer)1 |
| Center | 39.29°N, 60.07°E, on the northeastern lunar nearside near the limb1 |
| Naming | Approved by the IAU in 1935; named after Mashaallah ibn Asari, 8th–9th century astronomer3 |
| Floor | Relatively smooth, with mare deposits mapped on it and two clusters of dark pyroclastic deposits4 |
| Volcanic vents | Northern vent 2.9 x 2.3 km and 353 m deep; southern vent 2.3 x 2.2 km and 309 m deep4 |
Location and appearance
Messala lies in the thirteenth sector of the Moon, north of the prominent craters Cleomedes, Burckhardt, and Geminus on the northeastern limb region.3 • 2
The outer rim has been heavily eroded by subsequent small impacts, but most of the outer wall still keeps its original shape and shows terracing in places. Messala G, a 29 km crater, lies close to conspicuous rays of impact material that are visible under high angles of illumination, although the origin of that ray system cannot be determined from the available observations.2
Floor and volcanic deposits
Mare deposits have been mapped on the crater floor, and the level floor morphology is consistent with some degree of mare infilling.4
Pyroclastic deposits. Messala hosts two adjacent, partially overlapping clusters of dark pyroclastic material, designated Messala N (about 75 km²) and Messala S (about 103 km²). Several prominent volcanic vents sit within the deposits, aligned with and forming part of a group of short fractures, or graben, in the northern portion of the floor. The northern vent measures 2.9 x 2.3 km and is 353 m deep; the southern vent measures 2.3 x 2.2 km and is 309 m deep. The darkest material surrounds and lies between the linear vent complexes, including the overlap zone of the two deposits.4 The pyroclastic deposits may represent the last phase of volcanic activity within Messala, following earlier effusive eruptions that produced the mare infilling.4
Despite these volcanic features, Messala is not classified as a floor-fractured crater, a class of lunar craters with anomalously shallow floors cut by radial, concentric, or polygonal fractures that is generally attributed to shallow magmatic intrusion.4 • 5 This distinguishes it from nearby northeastern-limb craters such as Atlas, Franklin, and Gauss, which do host pyroclastic deposits and are classified as floor-fractured.4
Neighboring features
The crater sits within the region covered by the USGS geologic maps of the Cleomedes and Geminus quadrangles, near the boundary between the rugged terra of the eastern limb and the maria of the interior.2
References
- Gazetteer of Planetary Nomenclature: Messala, USGS Astrogeology Science Center
- Chu, A., Paech, W., Weigand, M. (2012). Cleomedes chapter, The Cambridge Photographic Moon Atlas, Cambridge University Press, pp. 39–40
- Lunar Craters Named After Muslim Astronomers, Muslim Memo
- A Comparative Analysis of Localized Pyroclastic Deposits (thesis, Cornell eCommons)
- Jozwiak, L. M. et al. (2012). Lunar floor-fractured craters: Classification, distribution, origin. Journal of Geophysical Research: Planets
Topic: Encyclopedia › Places and geography › Extraterrestrial places › Planetary surfaces and named features › Lunar surface features › Lunar craters
Initially written Oct 15, 2026 · Edited: Oct 25, 2026
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