Major Lunar Maria

1. Oceanus Procellarum 2. Mare Imbrium 3. Mare Cognitum 4. Mare Humorum
5. Mare Nubium 6. Mare Frigoris 7. Mare Serenitatis 8. Mare Vaporum
9. Mare Tranquillitatis 10. Mare Nectaris 11. Mare Humboldtianum 12. Mare Crisium
13. Mare Fecunditatis 14. Mare Marginis 15. Mare Smythii 16. Mare Australe
17. Mare Moscoviense 18. Mare Ingenii 19. Mare Orientale

Shown here is a map of the major lunar maria. These maria range from over 200 km to about 1200 km in size. They are typically about 500 m to 1500 m thick. However, each mare appears to contain many thinner basalt flows. Typical flow thicknesses appear to be 10-20 m. Thus, each mare records hundreds of overlapping eruption events. The map also shows a clear lack of major maria on the lunar farside. This probably reflects two changes in the lunar crust. First, the lunar surface is higher on farside than on the nearside. Second, the crust seems to be thicker on the lunar farside than on the nearside. These differences should make it harder for mare magmas to reach the surface on the lunar farside. They also explain why small mare patches are grouped together on the farside. The mare patches represent lava-filled craters. Most such craters lie in the bottoms of much larger and much older basins. On the nearside, such basins contain circular mare. On the farside, such basin filling volcanism is rare. Still, these basins contain both the lowest surfaces and the thinnest crust. Thus, mare volcanism is most likely inside these basins, especially where younger craters have dug into the basin floor. (Map prepared by G.W. Colton; published in NASA SP-362 (1978) and NASA SP-469 (1984).)

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