Alternative theories of the appearance of the moon

On December 13, 1972, the astronaut of Apollo 17 Harisson Schmitt approached the boulder in the sea of ​​Tranquility on the Moon. “This boulder has its own little path leading directly to the hill,” he told his commander Eugene Cernan, noting where the boulder was before slipping down the slope. Cernan took a few samples.

“Imagine what it would be like if you stood there before the boulder rolled off,” Cernan said thoughtfully. “Perhaps I’d rather not,” Schmitt replied.

The astronauts cut out pieces of the moon from the boulder. Then, using a rake, Schmitt scraped the dusty surface and picked up a pebble, which later would be called “troctolite 76536”.

That stone and its boulder brothers had to tell the story of how our moon appeared. In this creation story, recorded in countless textbooks and science and museum exhibits over the past forty years, the Moon was melted from a catastrophic collision between the germinal Earth and a solid world the size of Mars. Another world was called Teia, in honor of the Greek goddess who gave life to Selene, the moon. Theyah crashed so hard into the Earth that both worlds melted. The streams of molten material thrown out by Teia have then cooled down and hardened, forming a silvery companion, which we all know well.

Geologist-Astronaut Harrison Schmitt, Apollo 17 lunar module pilot, uses an adjustable sampling scoop to retrieve lunar samples during the second extravehicular activity (EVA-2), at Station 5 at the Taurus- Littrow landing site. The cohesive nature of the lunar soil is born out by the “dirty” appearance of Schmitt’s space suit. A gnomon is atop the large rock in the foreground. The gnomon is a stadia rod mounted on a tripod, and serves as an indicator of the gravitational vector and provides accurate vertical reference and calibrated length for determining size and position of objects in near-field photographs. The color scale of blue, orange and green is used to accurately determine color for photography. The rod of it is 18 inches long. The scoop Dr. Schmitt is using is 11 3/4 inches long and is attached to a tool extension which adds a potential 30 inches of length to the scoop. The pan portion, blocked in this view, has a flat bottom, flanged on both sides with a partial cover on the top. It is used to retrieve sand, dust and lunar samples too small for the tongs. The pan and the adjusting mechanism are made of stainless steel and the handle is made of aluminum.

But modern measurements of troctolite 76536 and other rocks from the Moon and Mars have questioned this theory. Over the past five years, many studies have identified a problem: the canonical hypothesis of a giant collision is based on assumptions that do not correspond to the evidence. If Teiya struck Earth, and later formed the Moon, the Moon must consist of Teiji’s material. But the Moon is not like Theia – or Mars, for that matter. Up to the very atoms, it looks almost the same as the Earth.

Faced with this discrepancy, the lunar researchers searched for new ideas to understand how the moon appeared. The most obvious solution may be the simplest, but it gives rise to other problems with the understanding of the young Solar system: perhaps Thea formed the Moon, but the Thay also consisted of a substance that was almost identical to the earth. Another option – the collision process mixed everything, homogenizing individual pieces and liquids in a cake, which was then cut into portions. In this case, the collision should have been extremely powerful, or there should have been several. The third explanation challenges our understanding of the planets. It may be that the Earth and the Moon, which we have today, have gone through strange metamorphoses and wild orbital dances that radically changed their rotation and future.

Bad news for Tei

To understand what could happen on the most important day for the Earth, you need to start with an understanding of the youth of the solar system. Four and a half billion years ago, the Sun was surrounded by a hot cloud of debris in the form of a donut. The star elements revolved around our newborn sun, cooling down and – over the years – merging into a process that we do not fully understand. First in clots, then in planetesimals, then into planets. These solids were hard and often colliding, evaporating and reappearing. It was in this incredibly hard starry billiards that the Earth and the Moon were forged.

To get the kind of moon that we have today, with its size, rotation and speed with which it departs from the Earth, our best computer models say that whatever the Earth faces, it must be something the size of Mars. Something more or less would already produce a system with a much larger angular momentum than we observe. A larger projectile would also throw too much iron into the Earth’s orbit and produce a much more iron-rich moon than we observe.

The first geochemical studies of troctolite 76536 and other breeds reinforced this story. They showed that the lunar rocks were to be born in the lunar magma ocean, which could in turn appear as a result of a giant collision. Throctolite swam in the molten sea as an iceberg in Antarctica. Based on these physical limitations, the scientists decided that the Moon was made from the remains of Teil. But there is a problem.

Let’s return to the young solar system. As the solid worlds collided and evaporated, their contents mingled, eventually settling in separate regions. Closer to the Sun, where it was hotter, the lighter elements were more likely to heat up and escape, leaving an excess of heavy isotopes (variations of elements with superfluous neutrons). Further from the Sun, the rocks were able to retain more water and lighter isotopes remained. Therefore, a scientist can explore a mixture of isotopes to determine in which part of the solar system it appeared, just as the accent is giving out the homeland of the person.

These differences are so strongly pronounced that they are used to classify planets and types of meteorites. Mars is so different from Earth, for example, that its meteorites can be identified by simply measuring the ratio of three different oxygen isotopes.

In 2001, using advanced methods of mass spectrometry, Swiss scientists again studied troctolite 76536 and other lunar samples. It turned out that their isotopes of oxygen are indistinguishable from those on the Earth. Geochemists have since studied titanium, tungsten, chromium, rubidium, potassium and other not very ordinary metals on Earth – and they all looked almost identical.

This is bad news for Teilh. If Mars is so different from Earth, Teiya – and hence the Moon – should also be different. If they are the same, it means that the moon had to be formed from the melted pieces of the Earth. The rocks collected by the Apollo, it turns out, will directly contradict what the physicist insists on.

“The canonical model is going through a serious crisis,” says Sarah Stewart, a planetologist at the University of California at Davis. “She has not yet been completely killed, but her current status is that she does not work.”

Moon out of steam

Stewart tried to rethink the physical limitations of this problem – the need for a shock body of a certain size that moves at a certain speed – against the backdrop of new geochemical evidence. In 2012, she and Matiya Zhuk, now working at the SETI Institute, proposed a new physical model for the formation of the moon. They said that the young Earth was a rotating dervish, the day of which lasted two or three hours, when Teiya hit it. The collision produced a disk around the Earth – like the ring of Saturn – but it lasted only 24 hours. Eventually, the disc cooled down and solidified, forming the Moon.

Dr. Sarah Stewart is a professor in the Department of Earth and Planetary Sciences. She is photographed with one of her graduate students at the KECK caves facility on the UC Davis campus.

Supercomputers are not powerful enough to fully model this process, but they showed that a projectile crashing into such a fast-paced world can cut off enough of the Earth, completely destroy Teiya and scrape off enough skins from both to create the Moon and Earth with the same isotopic ratios. Like a potter on a potter’s wheel.

In order for the explanation with the rapidly rotating Earth to be correct, however, there must be something else, slowed the speed of the planet’s rotation to the present state. In their work of 2012, Stewart and Chuck argued that, under certain orbital resonance interactions, the Earth had to transmit the angular momentum to the sun. Later Jack Wisdom of the Massachusetts Institute of Technology proposed several alternative scenarios for extracting angular momentum from the Earth-Moon system.

However, none of the explanations were satisfactory. The 2012 models could not explain the Moon’s orbit or its chemistry, says Stewart. And so, last year, Simon Lock, a graduate of Harvard University and a student of Stewart at the time, introduced an updated model that proposed a planetary structure that had not been proposed before.

In his opinion, each piece of the Earth and Teiji evaporated and formed a swollen, swollen cloud in the form of a thick bagel. The cloud rotated so quickly that it reached a point called the limit of joint rotation. At this outer edge of the cloud, the evaporated rock circled so fast that the cloud assumed a new structure, with a thick disc that circumvented the inner region. What is important, the disk was not separated from the central region in the same way as the rings of Saturn.

The conditions in this structure are indescribably hellish; There is no surface, instead of it clouds of molten rock, with each region of the cloud forming raindrops from the molten rock. The moon grew inside this pair, says Lok, before the steam finally cooled down and left the Earth-Moon system behind it.

Given the unusual characteristics of the structure, Locke and Stewart felt that she deserved a new name. They tried several versions before coming to the “sine”, which uses the Greek prefix “syn” meaning “together”, and the goddess Hestia, who represents the house, hearth and architecture. This word means “related structure,” says Stewart.

“These bodies are not what you think. And they do not look the way you thought they would look. ”

In May, Locke and Stewart published a paper on the physics of synas; Their work on the theme of lunar origin is still pending. They presented it to a conference of planetologists and said that their colleagues were interested, but they hardly agree with the idea. Perhaps, because siness is just an idea; Unlike ringed planets, which are many in the solar system, and protoplanetary disks, of which there are many in the universe, no one has ever seen one.

But this is an interesting way to explain the features of our moon, when our models do not seem to work.

Ten moons

Among the natural satellites of the solar system, the Earth’s Moon can be the most amazing because of its loneliness. Mercury and Venus do not have natural satellites, in part because of their proximity to the sun, whose gravitational influence makes the satellite orbits unstable. Mars has tiny Phobos and Deimos, which some consider to be captured by asteroids; Others speak in favor of the fall of large bodies on Mars. The gas giants have many satellites, both solid and soft.

Unlike these satellites, the Earth satellite also stands out for its size and physical load, which it carries. The moon is less than 1% of the Earth by mass, and the total mass of the satellites of the outer planets is less than 1/10 percent of their parents. More importantly, the Moon accounts for 80% of the angular momentum of the Earth system –
Moon. In other words, the Moon is responsible for 80% of the movement of the system as a whole. For outer planets this value is less than 1%.

Maybe Luna did not always carry all this burden. The satellite’s face demonstrates evidence of heavy bombardment; Why, then, should we believe that only one blow molded the Moon from the Earth? Perhaps the Moon was formed in the course of many clashes, says Raluka Rufu, the planetologist of the Weizmann Institute in Israel.

In a paper published last winter, she claimed that the Earth’s satellite might not be original. Instead, it became a collection of thousands of pieces – at least ten, based on its calculations. Shells flew at different angles and at different speeds to Earth and formed disks that merged into “fragments of the moons,” ultimately blinding the Moon that we know today.

Planetologists noted her work. Robin Kanup, Lunologist at the Southwest Research Institute and specialist in the theory of lunar education, says that the theory is worthy of consideration. However, more research is needed. Rufu is not sure if the debris moved in the same direction, just as the Moon is constantly looking in the same direction. If so, how could they even merge? This is to be clarified.

Meanwhile, others turned to another explanation of the similarity of the Earth and the Moon, which could have a very simple answer. From blue to the lunar belts, new physical models – and new physics – may be controversial. Perhaps the Moon is like the Earth only because Teiya was similar.

Same

The moon is not the only “earthly” thing in the solar system. Species like troctolite 76536 have the same ratio of oxygen isotopes as terrestrial rocks, as well as groups of asteroids – enstatite chondrites. The composition of oxygen isotopes in these asteroids is similar to that of the Earth, says Miriam Telus, a cosmochemist who studies meteorites at the Carnegie Institution in Washington. “One of the arguments is that they formed in the hot areas of the disk, which could be closer to the sun,” she says. Perhaps they formed alongside the Earth.

Some of these rocks gathered to form the Earth; Others formed Teiya. Enstatite chondrites are residual stones that never gathered and did not grow large enough to form mantles, nuclei and fully formed planets.

In January, Nicholas Daufas, a geophysicist at the University of Chicago, said that most of the stones that became the Earth were meteorites of the Enstatite type. He argued that everything that had been formed in one region would be collected from them. The planetary construction was carried out using the same mixed materials that we now find on Earth and the Moon; They look the same, because they are the same. The giant body that formed the Moon probably had an isotopic composition similar to that of the earth.

David Stevenson, a planetologist from the California Institute of Technology who has been studying the origin of the moon since Teiya’s hypothesis was first introduced in 1974, says he considers this work to be the most important contribution to the dispute over the past year. Because it is devoted to the problem geochemists are trying to solve for decades.

“This is a clever story about how to consider the various elements that get to Earth,” says Stevenson.

But not everyone agrees. There remain questions about the isotopic ratio of elements like tungsten, notes Stewart. Tungsten-182 is derived from hafnium-182, so the ratio of tungsten to hafnium works as a clock, determining the age of a particular breed. If one breed has more tungsten-182 than the other, you can safely say that the tungsten-rich breed was formed earlier. But the most accurate measurements show that the ratio of tungsten to hafnium at the Earth and the Moon is the same. Two bodies had to be in special conditions, so that it happened.

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