Oceanus Procellarum

Coordinates: 18°24′N 57°24′W / 18.4°N 57.4°W / 18.4; -57.4
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Oceanus Procellarum
Most of the dark region is Oceanus Procellarum and smaller maria, such as Imbrium and Serenitatis, that sit within its ring. Left of the centerline is Procellarum proper.
Coordinates18°24′N 57°24′W / 18.4°N 57.4°W / 18.4; -57.4
Diameter2,592 km (1,611 mi)[1]
EponymOcean of Storms

Oceanus Procellarum (/ˈsənəs ˌprɒsɛˈlɛərəm/ oh-SEE-ə-nəs PROSS-el-AIR-əm; from Latin: Ōceanus procellārum, lit.'Ocean of Storms') is a vast lunar mare on the western edge of the near side of the Moon. It is the only one of the lunar maria to be called an "Oceanus" (ocean), due to its size: Oceanus Procellarum is the largest of the maria ("seas"), stretching more than 2,500 km (1,600 mi) across its north–south axis and covering roughly 4,000,000 km2 (1,500,000 sq mi), accounting for 10.5% of the total lunar surface area.[2]


Like all lunar maria, Oceanus Procellarum was formed by ancient volcanic eruptions resulting in basaltic floods that covered the region in a thick, nearly flat layer of solidified magma. Basalts in Oceanus Procellarum have been estimated to be as young as one billion years old.[3] Unlike the other lunar maria, however, Oceanus Procellarum may or may not be contained within a single, well-defined impact basin.

Around its edges lie many minor bays and seas, including Sinus Roris to the north, and Mare Nubium and Mare Humorum to the south. To the northeast, Oceanus Procellarum is separated from Mare Imbrium by the Carpathian Mountains. On its north-west edge lies the 32 km wide Aristarchus ray crater, the brightest feature on the Near side of the Moon.[4] Also, the more-prominent ray-crater Copernicus lies within the eastern edge of the mare, distinct with its bright ray materials sprawling over the darker material.[5]


Moon – Oceanus Procellarum ("Ocean of Storms")
Ancient rift valleys – rectangular structure (visible – topography – GRAIL gravity gradients) (October 1, 2014).
Ancient rift valleys – context.
Ancient rift valleys – closeup (artist's concept).
Gravity anomalies (red) bordering the Procellarum region overlaid on a global elevation map

There are several hypotheses about the origin of Oceanus Procellarum and a related asymmetry between the near and far sides of the Moon. One of the most likely is that Procellarum was a result of an ancient giant impact on the near side of the Moon. The size of the impact basin has been estimated to be more than 3,000 kilometers, which would make it one of the three largest craters in the Solar System.[2]

Image of Apollo 12 landing site (center) used in mission planning (1.75 x 1.75 km)

The impact likely happened very early in the Moon's history: at the time when magma ocean still existed or just ceased to exist. It deposited 5–30 km of crustal material on the far side forming highlands. If this is the case, all impact related structures such as crater rim, central peak etc. have been obliterated by later impacts and volcanism. One piece of evidence in support of this hypothesis is concentration of incompatible elements (KREEP) and low calcium pyroxene around Oceanus Procellarum.[6][7]

Procellarum may have also been formed by spatially inhomogeneous heating during the Moon's formation.[6] The GRAIL mission, which mapped the gravity gradients of the Moon, found square formations resembling rift valleys surrounding the region beneath the lava plains, suggesting the basin was formed by heating and cooling of the lunar surface by internal processes rather than by an impact, which would have left a round crater.[8]

Other hypotheses include a late accretion of a companion Moon on the far side. The latter postulates that in addition to the present Moon, another smaller (about 1,200 km in diameter) moon was formed from debris of the giant impact. After a few tens of millions of years it collided with the Moon and due to a small collisional velocity simply piled up on one side of the Moon forming what is now known as far side highlands.[9]

Late lunar volcanism[edit]

Relatively recent (less than 2 bya) volcanic activity had been suspected in the Oceanus Procellarum due to the presence of relatively uneroded features. The 2020 Chang'e-5 sample return mission provided constraints on the age of Oceanus Procellarum, finding it to be 1963 ± 57 million years old – over a billion years younger than any other previously returned lunar sample. Late lunar volcanic activity was considered surprising as the Moon is much smaller than Earth; interior heat necessary for volcanism should have been lost three billion years ago, so volcanic rocks as late as those found in Oceanus Procellarum must require additional heat sources. Previous studies suggested that Oceanus Procellarum should have high concentrations of the heat-producing elements such as potassium, thorium, and uranium[a], but samples returned showed that the concentration of suspected radioactive elements is much lower than necessary to provide prolonged heating.[10]


The robotic lunar probes Luna 9, Luna 13, Surveyor 1 and Surveyor 3 landed in Oceanus Procellarum. Luna 9 landed southwest of Galilaei crater in 1966. Luna 13 landed southeast of Seleucus crater, later in 1966. Surveyor 1 landed north of Flamsteed crater (within the larger Flamsteed P) in 1966, and Surveyor 3 landed in 1967. The Chinese probe Chang'e 5 landed at Statio Tianchuan on Mons Rümker in Oceanus Procellarum in December 2020 and collected 1.73 kg (3.8 lb) of lunar rock samples.[11][12]

During the Apollo program, flight operations planners were concerned about having the optimum lighting conditions at the landing site, hence the alternative target sites moved progressively westward, following the terminator. A delay of two days for weather or equipment reasons would have sent Apollo 11 to Sinus Medii (designated ALS3) instead of ALS2—Mare Tranquillitatis; another two-day delay would have resulted in ALS5, a site in Oceanus Procellarum, being targeted.

During the November 1969 Apollo 12 mission, astronauts (Charles) Pete Conrad and Alan Bean landed the Lunar Module (LM) Intrepid nearly 165 meters from Surveyor 3 in Oceanus Procellarum.[13] Their landing site has become known as Statio Cognitum (Latin, "to be known from experience").[14]

See also[edit]


  1. ^ "Oceanus Procellarum". Gazetteer of Planetary Nomenclature. USGS Astrogeology. Retrieved 2010-08-23.
  2. ^ a b October 2012, Charles Q. Choi 29 (29 October 2012). "Moon's Mysterious 'Ocean of Storms' Explained". Space.com. Retrieved 2021-05-07.{{cite web}}: CS1 maint: numeric names: authors list (link)
  3. ^ Andrea Thompson 06 November 2008 (6 November 2008). "Signs of Late Volcanism Seen on Moon". Space.com. Retrieved 2021-05-07.{{cite web}}: CS1 maint: numeric names: authors list (link)
  4. ^ DK Space Encyclopedia: The Near Side of the Moon
  5. ^ "NASA – Copernicus". www.nasa.gov. Retrieved 2021-05-07.
  6. ^ a b Nakamura, R.; Yamamoto, S.; Matsunaga, T.; Ishihara, Y.; Morota, T.; Hiroi, T.; Takeda, H.; Ogawa, Y.; Yokota, Y.; Hirata, N.; Ohtake, M.; Saiki, K. (2012). "Compositional evidence for an impact origin of the Moon's Procellarum basin". Nature Geoscience. 5 (11): 775. Bibcode:2012NatGe...5..775N. doi:10.1038/NGEO1614.
  7. ^ Byrne, C. J. (2008). "A Large Basin on the Near Side of the Moon". Earth, Moon, and Planets. 101 (3–4): 153–188. Bibcode:2007EM&P..101..153B. doi:10.1007/s11038-007-9225-8. S2CID 121092521.
  8. ^ "NASA Mission Points to Origin of "Ocean of Storms" on Earth's Moon" (Press release). NASA. 2014-10-01. Retrieved 2014-10-02.
  9. ^ Jutzi, M.; Asphaug, E. (2011). "Forming the lunar farside highlands by accretion of a companion moon". Nature. 476 (7358): 69–72. Bibcode:2011Natur.476...69J. doi:10.1038/nature10289. PMID 21814278. S2CID 84558.
  10. ^ Che, Xiaochao; Nemchin, Alexander; Liu, Dunyi; Long, Tao; Wang, Chen; Norman, Marc D.; Joy, Katherine H.; Tartese, Romain; Head, James; Jolliff, Bradley; Snape, Joshua F.; et al. (2021-11-12). "Age and composition of young basalts on the Moon, measured from samples returned by Chang'e-5". Science. 374 (6569): 887–890. Bibcode:2021Sci...374..887C. doi:10.1126/science.abl7957. ISSN 0036-8075. PMID 34618547. S2CID 238474681.
  11. ^ Jones, Andrew (8 July 2021). "China's Chang'e 5 moon landing site finally has a name". Space.com. Retrieved 9 July 2021.
  12. ^ Jennifer Hauser and Zamira Rahim (16 December 2020). "China's Chang'e-5 mission returns to Earth with moon samples". CNN.
  13. ^ "Apollo 12 Mission Overview". www.lpi.usra.edu. Retrieved 2021-04-25.
  14. ^ "Pinpoint Landing on the Ocean of Storms | Lunar Reconnaissance Orbiter Camera". lroc.sese.asu.edu. Retrieved 2021-04-25.
  1. ^ due to the abundance of their radioactive isotopes providing heat from decay