This dominant area on the northeastern quadrant of the moon is also believed to be one of the oldest at 3.92 to 4.55 billion years of age. Covering an area of approximately 421,000 square km, Mare Tranquillitatis is characterized with a variety of interesting formations including the 210-km long rille Rima Cauchy, the 120-km long fault Rupes Cauchy, sinus formations to the north, east and west as well as Dorsa Barlow and the picturesque crater Maskelyne and its central peak. Of interest is the change in the color of mare floor as one approaches Mare Serenitatis immediately to the northwest and which is indicative of differential geological activity and history.

Note: Mare Tranquillitatis is one of the most recognized names and areas of the moon thanks to the dramatic events of July 20, 1969 and the landing of the Apollo 11 Lunar Module (The Eagle) followed by Neil Armstrong's infamous one small step at 22:57 UT-4. Slightly further northwest, the American probe Surveyor 5 soft-landed on September 8, 1967 to sample and photograph the immediate area in preparation for the Apollo 11 landing less than two years later. A complete enumeration of all landing sites for Apollo, Luna and Surveyor craft is available elsewhere on this site.

Note: The reimaging of Mare Tranquillitatis with more favourable colour and contrast will be attempted during the forthcoming lunations.