Oceanus Procellarum
Oceanus Procellarum stretches more than 2,500 kilometers across its north, south axis. It covers roughly 4 million square kilometers of the Moon's surface. This area accounts for 10.5% of the total lunar surface area. It stands as the largest lunar plain on Earth's satellite. No other lunar plain carries the title Oceanus or ocean. The region sits on the western edge of the near side of the Moon. To the northeast it meets Mare Imbrium across the Carpathian Mountains. Minor bays like Sinus Roris lie to the north. Smaller seas including Mare Nubium and Mare Humorum border the south. A 32 kilometer wide crater named Aristarchus marks the north-west edge. Its bright rays make it the brightest feature on the Near side of the Moon.
Ancient volcanic eruptions created basaltic floods that covered this region. Thick layers of solidified magma now form a nearly flat surface. Basalts in Oceanus Procellarum date back to one billion years ago. This age makes them significantly younger than most other lunar maria. Unlike typical maria, this region may not sit inside a single well-defined impact basin. The GRAIL mission mapped gravity gradients beneath the lava plains. These maps revealed square formations resembling rift valleys. Such shapes suggest internal heating processes rather than a round impact crater. Scientists found concentrations of incompatible elements known as KREEP around the area. Low calcium pyroxene also appears in high numbers nearby. These geological markers distinguish the plain from surrounding lunar features.
Scientists propose several theories regarding how this vast basin formed. One likely scenario involves an ancient giant impact on the near side. That impact basin might have exceeded 3,000 kilometers in size. It would rank among the three largest craters in the Solar System. The event occurred when the Moon's magma ocean still existed or had just ceased. Five to thirty kilometers of crustal material deposited on the far side. Later impacts and volcanism obliterated all original impact structures like rim peaks. Another hypothesis suggests spatially inhomogeneous heating during the Moon's formation. A late accretion theory posits a companion moon collided with Earth's satellite. That smaller moon measured about 1,200 kilometers in diameter. Its debris piled up on one side forming today's far side highlands.
The Chang'e-5 sample return mission arrived in December 2020 at Statio Tianchuan. This location sits on Mons Rümker within Oceanus Procellarum. Scientists collected 1,731 grams of lunar rock samples there. Analysis revealed rocks aged 1963 plus or minus 57 million years old. These specimens are over a billion years younger than any previously returned lunar sample. Volcanic activity this recent surprised researchers because the Moon is much smaller than Earth. Interior heat should have been lost three billion years ago. Additional heat sources must explain these young volcanic rocks. Previous studies suggested high concentrations of potassium thorium and uranium. Samples returned showed lower levels than necessary for prolonged heating. The presence of uneroded features had already hinted at recent activity before the mission.
Luna 9 landed southwest of Galilaei crater in early 1966. Luna 13 touched down southeast of Seleucus crater later that same year. Surveyor 1 set down north of Flamsteed crater within the larger Flamsteed P region. Surveyor 3 followed in 1967 to land within the oceanus area. These Soviet and American probes marked the first robotic footsteps on this plain. Each landing provided critical data about surface composition and terrain. The Chinese probe Chang'e 5 arrived decades later in December 2020. It collected samples from Statio Tianchuan on Mons Rümker. This modern mission expanded upon the foundational work of earlier unmanned explorers. Their combined efforts mapped the geological diversity of the western near side.
Flight operations planners sought optimum lighting conditions for lunar landings. Alternative target sites moved progressively westward following the terminator line. A two-day delay would have sent Apollo 11 to Sinus Medii instead. Another two-day delay would have targeted ALS5 a site in Oceanus Procellarum. Astronauts Charles Pete Conrad and Alan Bean landed the Lunar Module Intrepid during November 1969. They placed their craft nearly 165 meters from Surveyor 3. Their landing site became known as Statio Cognitum meaning to be known from experience. Strategic planning behind selecting this western zone prioritized both safety and scientific value. The proximity to Surveyor 3 allowed direct comparison between human and robotic exploration results.
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Common questions
What is the size of Oceanus Procellarum on the Moon?
Oceanus Procellarum stretches more than 2,500 kilometers across its north south axis and covers roughly 4 million square kilometers. This area accounts for 10.5% of the total lunar surface area.
When did volcanic activity occur in Oceanus Procellarum?
Basalts in Oceanus Procellarum date back to one billion years ago with samples from Chang'e-5 mission revealing rocks aged 1963 plus or minus 57 million years old. These specimens are over a billion years younger than any previously returned lunar sample.
Where does Oceanus Procellarum sit on the Moon?
The region sits on the western edge of the near side of the Moon. To the northeast it meets Mare Imbrium across the Carpathian Mountains while smaller seas including Mare Nubium and Mare Humorum border the south.
How was Oceanus Procellarum formed according to scientific theories?
Scientists propose that an ancient giant impact on the near side created a basin exceeding 3,000 kilometers in size when the Moon's magma ocean still existed. Another hypothesis suggests spatially inhomogeneous heating during the Moon's formation involving a late accretion theory where a companion moon collided with Earth's satellite.
Who landed at Statio Tianchuan within Oceanus Procellarum in December 2020?
The Chang'e-5 sample return mission arrived in December 2020 at Statio Tianchuan which sits on Mons Rümker within Oceanus Procellarum. Scientists collected 1,731 grams of lunar rock samples there for analysis.