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.png) Most of the dark region is Oceanus Procellarum and smaller maria, such asImbrium andSerenitatis, that sit within its ring. Left of the centerline is Procellarum proper. | |
| Coordinates | 18°24′N57°24′W / 18.4°N 57.4°W /18.4; -57.4 |
|---|---|
| Diameter | 2,592 km (1,611 mi)[1] |
| Eponym | Ocean of Storms |
Oceanus Procellarum (/oʊˈsiːənəsˌprɒsɛˈlɛərəm/oh-SEE-ə-nəsPROSS-el-AIR-əm; fromLatin:Ōceanus procellārum,lit. 'Ocean of Storms') is a vastlunar mare on the western edge of thenear side of theMoon. 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 ancientvolcanic eruptions resulting inbasaltic floods that covered the region in a thick, nearly flat layer of solidifiedmagma. 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, includingSinus Roris to the north, andMare Nubium,Mare Humorum andSinus Viscositatis [it][4] to the south. To the northeast, Oceanus Procellarum is separated fromMare Imbrium by theCarpathian Mountains. On its north-west edge lies the 32 km wideAristarchus ray crater, the brightest feature on the Near side of the Moon.[5] Also, the more-prominent ray-craterCopernicus lies within the eastern edge of the mare, distinct with its bright ray materials sprawling over the darker material.[6]
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 itone of the three largest craters in the Solar System.[2]
The impact likely happened very early in the Moon's history: at the time whenmagma 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 craterrim, central peak etc. have been obliterated by later impacts andvolcanism. One piece of evidence in support of this hypothesis is concentration of incompatible elements (KREEP) and low calciumpyroxene around Oceanus Procellarum.[7][8]
Procellarum may have also been formed by spatially inhomogeneous heating during the Moon's formation.[7] 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.[9]
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 thegiant 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 sidehighlands.[10]
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.[11]
Therobotic lunarprobesLuna 9,Luna 13,Surveyor 1 andSurveyor 3 landed in Oceanus Procellarum. Luna 9 landed southwest ofGalilaei crater in 1966. Luna 13 landed southeast ofSeleucus crater, later in 1966. Surveyor 1 landed north ofFlamsteed crater (within the larger Flamsteed P) in 1966, and Surveyor 3 landed in 1967. TheChinese probeChang'e 5 landed at Statio Tianchuan onMons Rümker in Oceanus Procellarum in December 2020 and collected 1.73 kg (3.8 lb) of lunar rock samples.[12][13]
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 toSinus 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 1969Apollo 12 mission,astronauts (Charles)Pete Conrad andAlan Bean landed the Lunar Module (LM)Intrepid nearly 165 meters from Surveyor 3 in Oceanus Procellarum.[14] Their landing site has become known as Statio Cognitum (Latin, "to be known from experience").[15]
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