Observations made by NASA's LRO lunar probe indirectly suggested that the Moon had emitted lava flows about 100 million years ago. Samples of material brought back to Earth by the Chinese Chang'e-5 mission now confirm this!
For a long time there has been debate over whether lunar craters are volcanic in origin or the result of meteorite and asteroid impacts. astronomersastronomers had hypothesized that lunar craters were remnants of volcanoesvolcanoes extinguished, including calderascalderasThe hypothesis that they could also be impact craters of celestial bodies slowly began to gain ground at the end of the 19th century.e century. The debate continued until the 1950s, but progress in space exploration clearly demonstrated that the proponents of impacts were largely right.
However, some of the features of the Moon's surface do indeed involve volcanic processes, such as the late volcanologistvolcanologist Haroun Tazieff thought so. We know this in particular thanks to the missions ApolloApollo which allowed samples of lunar rocks to be brought back to Earth and which are still being studied today. Magically, it is not necessary 50 years after the Apollo (United States), Luna (USSR) and VikingViking to be a member of a world-class research laboratory to own lunar or Martian meteorites nor to be a millionaire. It is possible to acquire them for a few dozen euros from serious suppliers such as Luc Labenne, Alain and Louis Carion or Jean Redelsperger.
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In 1610, when the Italian astronomer Galileo turned his telescope towards the Moon, he discovered what we know to be lunar basaltic lava plains that he mistook for seas. Galileo therefore named them mariafrom the Latin word for “seas.” A few decades later, in 1665, British chemist Robert Hooke proposed that the bowl-shaped depressions scattered across the lunar surface were volcanoes because of their similarity to the craters of the Phlegraean Fields in Italy. French astronomer Pierre-Simon Laplace proposed in the 18th centurye century that meteorites were volcanic projectiles ejected from lunar craters during major eruptions. This was ultimately not so far from the truth since some meteorites are indeed of lunar and volcanic origin although ejected from the Moon by asteroid impacts.
The Moon was born about 4.5 billion years ago. Smaller than the Earth, its stock of radioactive elements, which when disintegrating release heat, being less important, it cooled more quickly and seemed after the Apollo missions to be a dead star where the last volcanic eruptionsvolcanic eruptions had occurred more than one to two billion years ago. No chance of observing activity like that of Iceland at the moment so…
But are we really sure?
Young volcanoes on the Moon? To get a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © ScienceAtNASA
70 volcanic eruptions in 100 million years
On the visible face of the Moon, there are small irregular spots breaking up the lunar seas, called by their English name IMP, for Irregular Mare Patches. These are regions made up of rocks basalticbasaltic younger than the last phase of formation of the lunar maria, which occurred 1 to 1.2 billion years ago. This age is estimated from the local cratering rate of the surface of our satellite which was calibrated using rocks brought back by lunar missions. The less the region studied is covered with craters, the younger it is and its age can be obtained by dating the rocks formed at the time of the birth of the region and in this case often the date of cooling of the washedwashed of the seas.
In 2023, an international group of geologistsgeologists and American and German planetologists had published in Nature Geoscience an article that confirmed what had been suspected for some time already. Using the exceptional images taken with the mission's instruments Lunar Reconnaissance OrbiterLunar Reconnaissance Orbiter (LRO))whose resolutionresolution is of the order of 50 to 200 centimeters per pixelpixelthe researchers had managed to more precisely date 70 IMPs, whose sizes range from 100 to 5,000 meters. It appeared that they were the product of volcanic eruptions that occurred less than 100 million years ago.
The IMP Sosigenes is oval in shape with dimensions of about 3 kilometers wide and 7 kilometers long and a depth of about 300 meters. The number of craters on the basaltic lava flows that constitute it suggests that the eruptions that produced them took place only about 18 million years ago. © Nasa, GSFC, Arizona State University
The youngest IMP was probably the one found next to the crater Sosigenes so named in 1935 by theInternational Astronomical UnionInternational Astronomical Union to pay homage to the Greek astronomer Sosigenes of Alexandria. This impact crater is clearly visible in the vicinity of the Sea of Tranquility and to the north the bay of Sinus Honoris. According to the observations provided by LRO, the Sosigenes IMP would have formed only 18 million years ago, well after the disappearance of the dinosaurs on Earth. It therefore seemed clear now that the Moon remained volcanically active much longer than previously thought and that it could probably become so again in the near future, at least on the geological scale whose unit is the million years.
The IMP Ina is 3 kilometers wide and about 50 meters deep. Its floor is covered with numerous small mounds of lava. The number of craters observed on the mounds indicates that the eruptions that formed them took place about 33 million years ago. © Nasa, GSFC, Arizona State University
From LRO to Chang'e 5 via Kaguya
Let us recall that on December 16, 2020, a capsule carrying nearly two kilos of lunar samples landed in Mongolia. It brought back to Earth the mattermatter taken by the Chinese probe Chang'e 5Chang'e 5 which had landed in the region of Mons Rümker in the northern part of the Pacific Ocean StormsStormsin Latin Oceanus Procellarumthe largest of the lunar seas. Measuring more than 2,500 kilometers along its north-south axis, it is located to the west of the visible face of the Moon.
The Japanese Kaguya probe of the Jaxa had previously provided spectacular images of the flyoverflyover on orbitorbit low of the Ocean of Storms. But today, a team of Chinese researchers has just published in Science the results of their latest work on continuing the analysis of the 3,000 tiny glass beads discovered in the samples of regolithregolith Chang'e 5 lunar in Oceanus Procellarumexamining the chemical compositions, the texturestextures physicalphysical and the isotopesisotopes of sulfursulfur of these pearls to distinguish the glassesglasses potential volcanic glasses produced by meteorite impacts.
Meteorite impacts and volcanic eruption producing glass beads on the Moon. © T. Zhang and Y. Wang
They finally identified three pearls as being of volcanic origin, then used radiometric dating by the method UraniumUranium–LeadLead to determine that the volcanic pearls were formed during an eruption 123 ± 15 million years ago.
Selenologists add that volcanic pearls contain large amounts of potassiumpotassiumof phosphorusphosphorus and elements of rare earthsrare earthscalled KREEP which is the acronym in English constructed from the letters K (the atomic symbol for potassium), REE (Rare Earth Element – Rare earths) and P (for phosphorus), a geochemical component of certain impact breccias, basaltsbasalts Or noritesnorites melts already discovered in lunar rocks from the Apollo missions. The most important characteristic of KREEP is an increased concentration of so-called “incompatible” elements (which concentrate in phase liquidliquid during the crystallization of the magmamagma) and producing heat like uranium, thoriumthorium and potassium.
Kaguya flying over the western side of the Ocean of Storms, in Latin Oceanus Procellarum. © Jaxa
It turns out that the Procellarum KREEP terrane or PKT (in French: the KREEP terrain of Procellarum) is a vast lunar area located at the level of theOceanus Procellarum and of the Mare Imbrium. This terrain is rich in KREEP and analyses of samples brought back by the Apollo 14 mission indicated a high rate of thorium. Planetologists had already concluded that the richness in this element must also exist within the crustcrust and/or coatcoat lunar and that there was therefore a significant local heat source is almost certainly responsible for the longevity and intensity of the volcanismvolcanism on the visible face of the Moon at this location.
Selene (SELenological and ENgineeering Explorer) or Kaguya (かぐや) was the first true Japanese lunar space mission launched on September 14, 2007. It entered a circular polar orbit of 100 kilometers in mid-December, beginning its primary mission of 10 months, which was extended by 8 months. The mission ended in June 2009 when the space probe intentionally crashed on the surface of the Moon. It left impressive films of its flyby of the lunar surface as shown in this series of videos. © Jaxa, NHK
