Recently, astrophysicists, using space telescope Kepler has made another interesting discovery. While exploring the KOI-730 star system, they discovered that two of its four planets share a common orbit. Scientists believe that a similar phenomenon was once observed in the solar system. It's about about the hypothetical “double” of the Earth - Theia.
Planetologist Jack Lissauer of the Ames Research Center and his astrophysicist colleagues have calculated that the distance between the “neighboring” planets that share a common orbit is 60 degrees, and they orbit their solar-type star in 9.8 days. If you look at one of the planets from the position of the other, then it is visible in the sky as a bright light. At the same time, its glow is stable: it never flares up or becomes dimmer.
This situation has arisen due to “Lagrange points,” also called libration points (translated from Latin, this literally means “swinging”). These are points lying in the plane of the orbits of two massive bodies, in which a third object may be located with negligible light weight, while no other forces act on it except the gravitational influence from these two bodies of large mass. Gravity is balanced by centrifugal force, which allows this object remain motionless relative to massive bodies. The phenomenon was discovered in 1772 by mathematician Joseph Louis Lagrange.
In astronomy, Lagrange points are denoted by capital letters. Latin letter L, to which a numerical index from one to five is added. It is convenient to place artificial space objects at such points, since the nearest large celestial bodies will always be in the same position in relation to them. Now at various points in Lagrange solar system There are several spacecraft, including astrophysical observatories.
In our system, only small space objects such as asteroids can be detected at “Lagrange points”. However, the discovery made in the KOI-730 system serves as indirect confirmation of the impact theory of the formation of the Moon, or the “Big Splash” theory, put forward in 1975 by American astrophysicists Al Cameron, William Ward, William Hartmann and Donald Davis.
According to it, at the dawn of the formation of the solar system (about 4.6 billion years ago), a collision occurred between the Earth and planet Theia. This is hypothetical heavenly body the size of Mars was named by modern astrophysicists in honor mythological character Theia - one of the Titanide sisters, mother of Helios, Eos and Selene (goddess of the Moon). Presumably, Theia was located at the L4 Lagrange point, located in Earth's orbit. Then under the influence gravitational forces Between the Earth and the Sun, it moved into a chaotic orbit and, approaching the Earth, literally crashed into it. There was an explosion, after which Theia shattered into fragments. From them the Earth's satellite, the Moon, was later formed.
Richard Gott and Edward Belbrano from Princeton University managed to simulate this process on a computer. They concluded that Theia formed at exactly the same distance from the Sun as the Earth, and the collision occurred at a relatively low speed and somewhat tangentially, so our planet was not too damaged. By the way, the Moon was originally 20 times closer to the Earth than it is now, researchers believe.
Many facts support this turn of events. Firstly, none of the planets in the solar system, with the exception of Pluto, has a satellite as large in mass as the Moon. Secondly, the Moon has much less gravity than the Earth, and it contains much less iron than it should have. Thirdly, the oxygen isotopic composition of the Earth and the Moon is very similar.
Richard Gott and Edward Belbrano also believe that the formation of the Moon was crucial for the development of life on Earth. After all, the gravity of the Moon (the so-called lunar tides) smoothes out fluctuations in the Earth’s axis, stabilizing the Earth’s climate, making it more favorable for living organisms.
Scientists believe that there are other planetary systems in our Galaxy with Earth-like planets with large moons. It is there that there is a chance to find life, possibly intelligent.
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The Moon arose as a result of the so-called Giant Collision that occurred 4.5 billion years ago between proto-Earth and another protoplanet approximately the size of Mars, scientists are finally convinced. Despite the fact that this hypothesis of the origin of the Moon has always been prevalent, so far no indisputable evidence has been presented in its favor.
Of the more than one and a half hundred moons in the solar system, only our Moon is believed to have its own special origin. Other natural satellites either represent alien planetesimals or were born simultaneously with their parent planets from the same accretion disk. However, many signs, such as the low content of water and other volatile elements on the Moon, a very small core, its angular momentum similar to the Earth and others, forced scientists to suggest another scenario for its occurrence - the Giant Impact scenario.
The problem was that each planet in the solar system has its own unique isotopic composition, therefore, for that protoplanet, it was called Theia, it would be reasonable to assume an isotopic composition different from that of Earth.
According to many calculations, Theia contributed from 70 to 90% of her mass to the creation of the Moon. True, there are other versions, according to which Theia hit the Earth too tangentially, tearing out a large piece of mass from it and then flying off somewhere, and she gave no more than 8% of her substance to the Moon. Another difficulty was that upon impact with the proto-earth, Theia could give up to 50% of its isotopic signature to it, so the search for differences became even more difficult.
But one way or another, so far no isotopic differences have been discovered in lunar and terrestrial soils.
Although they seemed to measure it accurately, down to five parts per million.
A new installation created at the University of Göttingen allowed researchers to measure the isotopic composition of materials much more accurately. Having decided to compare lunar and terrestrial basalts on it, scientists first used the substance of lunar meteorites, but did not find any difference with terrestrial materials: in their opinion, celestial aliens from the Moon during their stay on our planet were fairly contaminated with local isotopes. Therefore, their next step was to study samples of lunar soil brought to Earth by three expeditions of the Apollo mission.
Scientists have focused their attention on oxygen isotopes.
As a result, in all three samples brought from the Moon, the oxygen-17 content was 9 hundred thousandths of a percent higher than what was found in terrestrial samples.
“This difference is very small, but it is there,” says Daniel Herwardz, who leads the study. “And it leads us to two conclusions. Firstly, we can say with confidence that the Giant Impact actually happened. Secondly, it gives us the opportunity to say something about the geochemistry of Theia. The next goal is to find out how much material the Moon actually got from Theia."
Hervardts doesn’t believe in 70-90%. He believes that, most likely, the Moon inherited from the Earth and Theia, as it should be inherited from parents, 50/50.
And finally, the question remains unanswered: where did Theia go after the collision, what happened to her, did she die in subsequent collisions, fell on some Jupiter, or became part of a long-known planet.
Similar materials
New materials
The collision of the Earth with the hypothetical planet Theia probably formed the Moon in a completely different way than previously thought: the powerful impact evaporated most solid rocks of our planet, sharply inflating it in size, and it was from the outer layers of this vapor that our natural satellite arose.
American scientists have developed a new method for determining the concentration of potassium isotopes and, on its basis, created an exotic theory of the formation of the Moon, which had never before been considered by the scientific community. The corresponding article was published in the journal Nature.
Since the 1970s, it has been generally accepted that the Moon formed when a hypothetical Mars-sized planet (Theia) struck the proto-Earth 4.5 billion years ago. However, over the past 15 years, a number of data have been inconsistent with this idea. Almost any model of such an impact shows that the Moon must be at least 60 percent formed from Theia. But an analysis of the composition of the lunar soil - both Soviet and American - indicated that there is the same ratio of oxygen isotopes as on Earth. It is also known that chemical composition planets formed in different regions of the solar system must differ. American rovers record that the isotopic composition for Mars is completely different from that for Earth.
The generally accepted model of the formation of the Moon.
To explain this contradiction, in 2015 it was proposed new model, according to which the collision of the bodies was “head-on” and so powerful that the main part of both planets evaporated from heating. The rocks became gas, but its temperature was so high that instead of a silicate atmosphere, a continuous cover of silicate supercritical fluid appeared above the planet's core. This is the name given to the state of matter when the temperature and pressure in it are higher critical point. Because of this, it simultaneously has the properties of both a gas and a liquid. For example, a supercritical fluid easily penetrates obstacles like a gas, but at the same time dissolves solids like a liquid.
In such an environment, the matter of Theia and the proto-Earth could quickly mix and become chemically homogeneous within a short time. The hypothesis had two main flaws. Firstly, if this was so, at first glance it was impossible to either refute or convincingly prove it. After all, the composition of the Earth and the Moon would then be the same. Secondly, the script turned out to be too exotic. It required the evaporation of the main part of our planet after the impact and its increase in volume by 500 times. The diameter of the planet could then reach 100,000 kilometers (almost like Saturn). That's about eight times larger than today, and more like a gas giant planet than the Earth we know.
However, now scientists from the USA, having created a more accurate method of analysis for potassium isotopes, have established that lunar rocks contain slightly more potassium-41 than terrestrial ones (by 4 ten-thousandths). The only scenario that can correctly explain such a difference is different speed condensation of potassium-41 from a cloud of hot steam. The outer layers of the proto-Earth, swollen after the impact, would have been tens of thousands of kilometers from its center and began to cool earlier. As it cooled, heavier potassium-41 was deposited in the outer layers more intensively than in the inner ones. Since the outer layers later became the Moon, and the inner layers became the present-day Earth, the satellite naturally ended up with slightly more potassium-41 than on our planet.
If this process took place in a vacuum, it would give a big difference in the concentration of potassium-41. Since the differences are still quite small, calculations show that the condensation of potassium-41 in the substance of the future Moon took place at a pressure of 10 atmospheres. This is a fairly large value, which indicates that the hypothesis of the evaporation of the proto-Earth after the collision with Theia is most likely correct. No matter how difficult it might be to imagine today, in the area where the future Moon was formed there existed a supercritical fluid from the evaporated solid rocks of our planet. Over time, it gradually crystallized into the rocks of the modern Moon. And the rest of the “excess” matter settled back on our planet, forming its outer layers.
According to this theory, Theia formed 4.6 billion years ago, like other planets in the Solar System, and was similar in size to Mars.
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The science
The planet Neptune used to be also classified as hypothetical; it had never been seen, but its existence was assumed.
In fact, scientists have assumed and continue to assume the existence of more planets.
Some fall off this list over time, others may have actually existed in the past, and probably even still exist today.
10. Planet X
In the early 1800s, astronomers knew of the existence of all the major planets in our solar system except Neptune. They were also familiar with Newton's laws of motion and gravity, which were used to predict the movements of planets.
When correlating these predictions with the actual observed movement, it was noticed that Uranus did not "go" where it was predicted. Then the French astronomer Alexis Bouvard asked the question: could the gravity of an invisible planet shift Uranus from its intended course.
After the discovery of Neptune in 1846, many astronomers decided to test whether its gravitational force was strong enough to explain the observed motion of Uranus. The answer turned out to be negative.
Perhaps there is another invisible planet? The existence of a ninth planet has been proposed by many astronomers. The most meticulous searcher for the ninth planet was the American astronomer Percival Lowell, who named the wanted object “Planet X”.
Lowell built an observatory with the goal of finding Planet X, but never found it. 14 years after his death, astronomers discovered Pluto, but its gravitational force was also not strong enough to explain the observed movement of Uranus, so scientific world continued to search for Planet X.
The search continued until Voyager 2 passed Neptune in 1989. It was then that it was discovered that Neptune's mass had been measured incorrectly. Updated mass calculations explain Uranus' motion.
Unknown planet
9. Planet between Mars and Jupiter
In the 16th century, Johannes Kepler noticed the existence of a huge gap between the orbits of Mars and Jupiter. He assumed that there maybe a planet, but did not look for her.
After Kepler, many astronomers began to notice patterns in the orbits of planets. The approximate sizes of the orbits from Mercury to Saturn are 4, 7, 10, 16, 52, 100. If you subtract 4 from each of these numbers, you get 0, 3, 6, 12, 48 and 96.
It is noteworthy that 6 =3+3, 12=6+6, 96=48+48. Between 12 and 48 there remains a strange emptiness.
Astronomers were puzzled by the question of whether they had missed a planet, which, according to calculations, should be located between Mars and Jupiter. As the German astronomer Elert Bode wrote: “After Mars, a huge space was discovered in which not a single planet had yet been identified. Can we believe that the founder of the Universe left this space empty? Of course not".
When Uranus was discovered in 1781, the size of its orbit fit neatly into the pattern described above. This seemed like a law of nature, which later became known as Bode's law or Titius-Bode's law, however, the notorious gap between Mars and Jupiter still remained.
Elert Bode
A Hungarian astronomer named Baron Franz von Zach also became convinced that Bode's law works, which means that There is an undiscovered planet between Mars and Jupiter.
He spent several years searching, but never found anything. In 1800, he organized a group of several astronomers who systematically carried out research. One of them was the Italian Catholic priest Giuseppe Piazzi, who in 1801 discovered an object whose orbit exactly the same size.
However, the object named Ceres, turned out to be too small to be called a planet. In fact, Ceres was considered an asteroid for many years because it was the largest in the main asteroid belt.
Today, Ceres is classified as a dwarf planet, as is Pluto. It is worth adding that Bode's law stopped working when Neptune was found because the size of its orbit did not fit the accepted pattern.
Galaxy: unknown planets
8. Theia
Theia is the name given to a hypothetical, Mars-sized planet that likely collided with Earth about 4.4 billion years ago, possibly resulting in the formation of the Moon. It is assumed that the name of the planet was given by the English geochemist Alex Halliday. This was the name of the mythological Greek titan who gave life to the moon goddess Selene.
It is worth noting that the origin and formation of the Moon is still unknown. the subject of active scientific discussion. While the above story is the main version (Giant Impact Hypothesis), it is not the only one.
Perhaps the moon was somehow "captured" by the Earth's gravitational field. Or maybe the Earth and the Moon formed in pairs at about the same time. It is important to add that the Earth, at the very beginning of its formation, probably suffered from collisions with many large celestial bodies.
7. Vulcan
Uranus was not the only planet whose observed motion did not match predictions. Another planet had such a problem - Mercury.
The discrepancy was first discovered by mathematician Urban Le Verrier, who discovered that the lowest point in Mercury's elliptical orbit (perihelion) was moving around the Sun faster than his calculations showed.
The discrepancy was minor, but additional observations showed that the mathematician was right. He suggested that the discrepancies are caused by the gravitational field of an undiscovered planet orbiting within Mercury's orbit, which he named Vulcan.
Urban Le Verrier
This was followed by numerous "observations" of Vulcan. Some observations turned out to be simply sunspots, but there were others made by respected astronomers that seemed plausible.
When Le Verrier died in 1877, he believed that Vulcan's existence confirmed. However, in 1915 it was published general theory Einstein's relativity, and it turned out that the movement of Mercury was predicted correctly.
The volcano disappeared, but people continued to look for objects orbiting the Sun inside the orbit of Mercury. Of course, there is nothing “planet-like” there, but asteroid-sized objects that have been called “live” there may well “live” volcanoids."
6. Phaeton
German astronomer and physician Heinrich Olbers discovered the second known asteroid, named Pallas, in 1802. He suggested that the two asteroids found could be fragments of an ancient planet, which was destroyed under the influence of some internal forces or during a collision with a comet.
It was implied that there were more objects besides Ceres and Pallas, and indeed, two more were soon discovered - Juno in 1804 and Vesta in 1807.
The planet that supposedly broke up to form the main asteroid belt became known as Phaeton, named after the character Greek mythology, who was driving the sun chariot.
However, the Phaeton hypothesis ran into problems. For example, the sum of the masses of all main belt asteroids is much less than the mass of the planet. In addition, there are many differences between asteroids. How could they come from the same "parent"?
Today, most planetary scientists believe that asteroids form due to the gradual sticking together of small fragments.
The unknown in space
5. Planet V
This is another hypothetical planet between Mars and Jupiter, but the reasons why it is believed to have once existed are completely different from the above.
The story begins with the Apollo mission to the moon. Apollo astronauts brought many moon rocks to Earth, some of which were formed by melting rocks during the period when something like an asteroid collided with the Moon and generated enough heat to melt the stone.
Scientists have used radiometric dating to reveal when these rocks cooled. They concluded that the coldest period is approximately 3.8 - 4 billion years ago.
It appears that many comets and asteroids collided with the Moon during this period of time. This period is known as the "Late Heavy Bombardment" (LTB). "Late" because it happened after most of the others.
Previously, collisions in the solar system occurred with enviable regularity, but now time has passed. In this regard, the question arises: what happened to the temporarily increased number of asteroids hitting the Moon?
About 10 years ago, John Chambers and Jack J. Lissauer suggested that the cause may have been a long-lost planet they called " Planet V".
According to their theory, Planet V was between the orbit of Mars and the main asteroid belt before the gravity of the inner planets forced Planet V into the asteroid belt, where it threw off the trajectories of many of them, ultimately leading to their collision with Moon.
It is also assumed that Planet V collided with the Sun. This hypothesis has been met with criticism because not everyone agrees that a PTB occurred, but even if it did, there must be other possible explanations other than the presence of Planet V.
4. Fifth gas giant
Another explanation for the PTB is the so-called Nice - a model named after French city, where it was first developed. According to this model, Saturn, Uranus and Neptune are outer gas giants– originated in small orbits surrounded by a cloud of asteroid-sized objects.
Over time, some of these smaller objects passed near gas giants. Such close encounters contributed to the expansion orbits of the gas giants, although at a very slow pace.
Jupiter's orbit actually became smaller. At some point, the orbits of Jupiter and Saturn entered into resonance, as a result of which Jupiter began to revolve around the Sun twice, while Saturn had time only once. This caused chaos.
By solar system standards, everything happened very quickly. The nearly circular orbits of Jupiter and Saturn tightened, and Saturn, Uranus, and Neptune collided several times. The cloud of small objects was also agitated.
In total this led to PTB. After everything passed, Jupiter, Saturn, Uranus and Neptune “acquired” the orbits that they have to this day.
This model can also be used to describe other features of the solar system, such as the Trojan asteroids of Jupiter, however, the original model does not explain everything. It needs modification.
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