The retelling of the story of the birth of our solar system has been very monotonous for many years. It all began billions of years ago with a dark and slowly rotating cloud of gas and dust. The cloud contracted, forming the Sun at its center. Over time, eight planets and many smaller bodies such as . Since then, the planets have been circling the Sun and their movements are as precise and predictable as a clockwork.
According to relatively new theory disk instability, accumulations of dust and gas are associated early in the life of the Solar System. Over time, these clusters slowly collapse into a giant planet. As scientists continue to study planets within the solar system, as well as around other stars, they will better understand how gas giants formed.
Most big problem for the main accretion is the creation of temporary giant gas giants quickly enough to capture the lighter components of their atmosphere. "They showed that the remaining pebbles from this formation process, previously thought to be inconsequential, could actually be a huge solution to the problem of planet formation," Levison said.
IN Lately astronomers are discovering facts that refute this old fairy tale. Compared to the design of thousands of recently discovered exoplanetary systems, the most character traits Our solar system—its inner rocky planets, outer gas giants, and lack of planets within Mercury's orbit—looks rather strange. By simulating the past on computers, we see that these quirks were the product of a wild youth. The history of the solar system needs to be rewritten to include far more drama and chaos than most of us expected.
Levison and his team built on this research to more precisely determine how tiny rocks could form the planets seen in the galaxy today. While previous simulations, both large and medium-sized objects consumed their pebble-sized cousins with relatively constant speed Levison's modeling suggests that the larger objects acted more like bullies, plucking pebbles from the middle masses to grow at a much faster rate.
Initially, scientists believed that planets formed in the same part of the solar system in which they live today. The discovery of exoplanets has shaken things up, showing that at least some of the most massive objects can migrate. Big circle rocks and ice surrounded them, about 35 times the distance from the Earth to the Sun, just beyond the modern orbit of Neptune. They named this model Nice after the city in France where they first discussed it.
New option stories tell of wandering planets expelled from their homes, of lost worlds, who perished long ago in the fiery heat of the Sun, and about lonely giants thrown into the cold depths at the border of interstellar space. By studying these ancient events and the “scars” they left behind, such as a proposed ninth planet that may be hiding beyond the orbit of Pluto, astronomers are building a coherent picture of the most important formative eras of the solar system against the backdrop of a new understanding of cosmic processes.
When the planets interacted with smaller bodies, they scattered most of them into the sun. The process forced them to trade energy with objects, sending Saturn, Neptune and Uranus further into the solar system. Eventually the small objects reached Jupiter, which sent them to the edge of the solar system or out of it entirely.
The movement between Jupiter and Saturn drove Uranus and Neptune into even more eccentric orbits, sending the pair through the remaining disk of ice. Some of the material was thrown inside where it impacted terrestrial planets during the late heavy bombardment. Other material was hurled outward, creating the Kuiper Belt.
Classical solar system
Planets are a by-product of star formation, which occurs in the depths of giant molecular clouds that exceed our Sun in mass by 10 thousand times. Individual densities in the cloud are compressed under the influence of gravity, forming a luminous protostar at its center, surrounded by a wide opaque ring of gas and dust - a protoplanetary disk.
As they slowly moved outwards, Neptune and Uranus traded places. Eventually, interactions with the remaining debris caused the pair to plunge into more circular paths as they reached their current distance from the sun. Along the way, it is possible that one or even two other giant planets were kicked out of the system.
“In the early days the solar system was very different, with much big amount planets, perhaps as massive as Neptune, forming and scattered in different places,” Nesvorny said on the site. The solar system did not complete the process of formation after the formation of the planets. Earth stands out among the planets because of its high water content, which many scientists believe contributed to the evolution of life. But the planet's current location was too warm for it to collect water in the early solar system, suggesting that the life-giving liquid could have been delivered after it was grown.
For many decades, theorists have modeled the protoplanetary disk of our Sun, trying to explain one of the the most important features Solar system: its division into groups of rocky and gas planets. The orbital periods of the four Earth-like planets fall between the 88-day Mercury and the 687-day Mars. In contrast, the known gas giants have much more distant orbits with periods ranging from 12 to 165 years and together have more than 150 times the mass of the planets terrestrial group.
But scientists still do not know the source of this water. The asteroid belt creates another potential source of water. Some of them showed signs of changes made to early dates their lives, which hint that water interacts with their surface in some form. The impact of meteorites could become another source of water for the planet.
Recently, some scientists believe that early Earth was too hot to collect water. They argue that if the planet formed quickly enough, it could collect necessary water from the ice grains before they evaporate. While the Earth was supported by its water, Venus and Mars would probably have been exposed to important fluid in much the same way. The rising temperatures on Venus and the evaporating atmosphere on Mars prevented them from holding water, but the result was the dry planets we know today.
Both types of planets are believed to have been born in a single formation process in which solid grains of dust, racing in the turbulent vortex of a gas disk, collided and stuck together to form kilometer-scale bodies called planetesimals (much like on the unswept floor of your kitchen, air currents and electrostatic forces roll up dust particles). balloons). The largest planetesimals had the greatest gravitational attraction and grew faster than others, attracting fine particles to its orbit. Probably over the course of a million years, in the process of being compressed from the cloud, the protoplanetary disk of our Solar System, like any other in the Universe, was teeming with planetary embryos the size of the Moon.
In the previous section we discussed the formation of a star through the collapse of a large cloud of gas. It is worth noting that the eight planets in our solar system make up two different groups; the four planets closest to the Sun make up the rocky terrestrial planets, and the four planets farthest from the Sun make up the gaseous terrestrial planets. Why do objects formed from the same cloud of gas have different compositions? The answer lies in where these objects formed relative to parent star, our Sun.
After the solar nebula collapsed to form our Sun, a disk of material formed around nova. The temperature on this protoplanetary disk was not uniform. Because the various materials condense at different temperatures, our solar system forms Various types planets. Dividing line for different planets in our solar system is called the frost line. In the simulation below, notice where hydrogen and helium condense in the solar nebula.
The largest embryo was located directly behind modern belt asteroids, far enough from the light and heat of the newborn Sun, where ice was preserved in the protoplanetary disk. Beyond this “ice boundary,” embryos could feast on abundant deposits of planet-building ice and grow to enormous sizes. As usual, “the rich get richer”: the largest embryo grew faster than others, raking out gravitational field most available ice, gas and dust from the surrounding disk. In just about a million years, this greedy embryo grew so large that it became the planet Jupiter. This was the decisive moment, theorists thought, when the architecture of the solar system split in two. Left behind Jupiter, the other giant planets of the solar system turned out to be smaller because they grew more slowly, capturing with their gravity only the gas that Jupiter did not have time to capture. And the inner planets turned out to be even much smaller, since they were born inside the ice boundary, where the disk was almost devoid of gas and ice.
Hydrogen compounds such as water and methane usually condense when low temperatures and remain gaseous inside the frost line, where temperatures are higher. Heavier rocky and metallic materials are better suited to condensation at higher temperatures. high temperatures. Thus, the inner planets are made almost entirely of rock and metal and form a group known as the terrestrial planets.
How were the terrestrial planets formed?
After more heavy elements and the minerals were condensed into solid chunks of rock, all orbiting the Sun at about the same speed. As you can imagine, collisions between objects moving at the same speed are less destructive than collisions between objects moving at the same speed. at different speeds. Thus, when rocks orbiting the Sun move close to each other, they stick together more often than they destroy each other. These pieces gradually grow in a process called accretion.
Exoplanetary revolution
When astronomers began discovering exoplanets two decades ago, they began testing theories of solar system formation on a galactic scale. Many of the first discovered exoplanets turned out to be “hot Jupiters”, that is, gas giants, rapidly orbiting their stars with periods of only a few days. The existence of giant planets so close to the blazing surface of a star, where ice is completely absent, is completely contradictory classic painting formation of planets. To explain this paradox, theorists have proposed that hot Jupiters form far away and then somehow migrate inward.
When they are large enough, gravity forces them into spherical shapes. Outside the freezing line, temperatures are colder and hydrogen compounds can condense into ice. Rock and metal are still present in the outer solar system, but both are outnumbered and outweighed by hydrogen compounds. Thus, planetesimals formed in the outer solar system consist mainly of hydrogen compounds with traces rock and metal. Hydrogen and helium do not condense in the solar nebula and are quite abundant in large orbiting objects in the outer solar system.
Moreover, based on data from thousands of exoplanets discovered in surveys such as those from NASA's Kepler Space Telescope, astronomers have come to the alarming conclusion that solar system twins are quite rare. The average planetary system contains one or more super-Earths (planets several times large Earth) with orbital periods shorter than about 100 days. And giant planets like Jupiter and Saturn are found in only 10% of stars, and even less often do they move in almost circular orbits.
As the outer planetesimals continued to grow, their gravity increased. The surrounding material, primarily hydrogen and helium, becomes increasingly attractive to planets as they grow in size and planetesimals expand more and more.
On next questions answered astronomer Dr. Kathy Imhoff from Scientific Institute space telescope. Do all planets have seasons? What causes seasons? The Earth is tilted relative to its orbit around the Sun. Therefore, when our North Pole tilted towards the sun, we get summer in the Northern Hemisphere. When South Pole leans towards the sun, we get winter. Therefore, if a planet is tilted relative to its orbit around the Sun, it must have seasons. Venus - 23 degrees inclination, Earth - 5, Mars - 24, Jupiter - 3, Saturn - 27, Uranus - 98, Neptune -.
Deceived in their expectations, theorists realized that “several important details» classical theory The formation of our planetary system requires a better explanation. Why is the inner Solar System so low-mass compared to its exoplanet counterparts? Instead of super-Earths, it has small, rocky planets, and none within Mercury's 88-day orbit. And why are the orbits of the giant planets near the Sun so round and wide?
But you can see that most planets have tilts like Earth, so they must have seasons. In winter its ice caps grow, in summer they shrink. Jupiter has very little tilt, so it experiences no noticeable seasons. But Neptune turned completely on its side!
He must have very strange times of the year! How did the planets get their names? Five of the planets were known to people thousands of years ago. They are bright enough to be seen with the naked eye and move relative to the stars. The name of the planet comes from Greek word"wanderer". They named planets for some of their gods. Mercury was the Roman god of trade and cunning, and also the Messenger of the gods, Venus was the goddess of love, Saturn was the god Agriculture, and in the end everyone decided to stick with Roman names from mythology.
Obviously, the answers to these questions lie in the shortcomings of the classical theory of planet formation, which does not take into account the variability of protoplanetary disks. It turns out that a newborn planet, like a life raft in the ocean, can drift far from its birthplace. After the planet has grown, its gravity begins to influence the surrounding disk, exciting spiral waves in it, the gravity of which already affects the movement of the planet itself, creating powerful positive and negative feedbacks between the planet and the disk. As a result, an irreversible exchange of momentum and energy can occur, allowing young planets to embark on an epic journey across their parent disk.
So, new planet, was finally named Uranus for the father of the Titans. was named Neptune, for the god of the seas. Pluto was named after the god of the underworld. Most moons and some asteroids are also called Roman mythology. What did the first planet discover? What equipment did they use? Five planets have been known since ancient times - Mercury, Venus, Mars, Jupiter and Saturn. First new planet was Uranus. It was discovered by the English astronomer Sir William Herschel in Herschel, who was one of the first modern astronomers.
Herschel wanted to name the planet after King George, but no one else liked it, so they named it Uranus. Herschel and his sister Charlotte used several reflecting telescopes, some of which were based on designs developed by Sir Isaac Newton. The largest was over 40 feet long and had a mirror 48 inches across. It was taken with a frame made of wood, and they were supposed to help the assistants move along ropes and pulleys. It was the most large telescope in the world until 100 years later.
If we take into account the process of planetary migration, then the boundaries of the ice within the disks no longer play a special role in the formation of the structure of planetary systems. For example, giant planets born beyond the ice boundary can become hot Jupiters by drifting towards the center of the disk, that is, traveling along with gas and dust in a spiral towards the star. The trouble is that this process works too well and seems to occur in all protoplanetary disks. Then how to explain the distant orbits of Jupiter and Saturn around the Sun?
Which planet was formed first and how was it formed? We think the planets all formed at the same time. However, the sun probably formed first. The remaining gas and dust remained in the disk around the sun. At this disk, material began to compress and form “planetesimals.” These are small rocky bodies, something like asteroids. They crashed into each other and eventually formed the inner planets. At the same time, planetesimals formed the cores of the outer planets Jupiter and Saturn.
Due to their strong gravity, they picked up a lot of gas. Uranus and Neptune did this too, but there was less gas because Jupiter and Saturn got it first. The asteroid belt may be leftover planetesimals that never formed a planet because Jupiter's strong gravity did not keep it from forming.
Change of tack
The first hint of a convincing explanation came in 2001 from a computer model by Frederic Masset and Mark Snellgrove of Queen Mary University of London. They simulated the simultaneous evolution of the orbits of Saturn and Jupiter in the protoplanetary disk of the Sun. Because of Saturn's smaller mass, its migration toward the center is faster than that of Jupiter, causing the orbits of the two planets to move closer together. Eventually the orbits reach a certain configuration known as mean motion resonance, in which Jupiter orbits the Sun three times for every two orbital periods of Saturn.
Two planets connected by mean motion resonance can exchange momentum and energy back and forth with each other, much like an interplanetary game of hot potato tossing. Due to the coordinated nature of resonant disturbances, both planets exert an enhanced gravitational influence on each other and on their surroundings. In the case of Jupiter and Saturn, this “swing” allowed them to collectively influence the protoplanetary disk with their mass, creating a large gap in it with Jupiter by inside and Saturn on the outside. Moreover, because of its greater mass Jupiter attracted the inner disk more strongly than Saturn, the outer one. Paradoxically, this caused both planets to change their motion and begin to move away from the Sun. like this sudden change The migration direction is often called the grand tack because of its similarity to the movement of a tacking sailboat going upwind.
In 2011, ten years after the birth of the tack change concept, a computer model by Kevin J. Walsh and his colleagues at the Observatory Cote d'Azur in Nice (France) showed that this idea well explains not only the dynamic history of Jupiter and Saturn, but also the distribution of rocky and icy asteroids, as well as low mass Mars. As Jupiter migrated inward, its gravitational influence captured and moved planetesimals on its way through the disk, scooping and pushing them forward like a bulldozer. If we assume that Jupiter, before turning back, migrated towards the Sun to the distance of the current orbit of Mars, then it could drag ice blocks total mass more than ten Earth masses into the region of the Earth-like planets of the solar system, enriching it with water and other volatile substances. The same process could have created a clear outer boundary at the inner part of the protoplanetary disk, stopping the growth of the nearby planetary embryo, which eventually became what we call Mars today.
Jupiter attack
Despite the fact that the tack change scenario in 2011 looked very convincing, its relation to others unsolved mysteries our solar system, such as complete absence planets within Mercury's orbit remained unclear. Compared to others planetary systems, where super-Earths are densely packed, ours seems almost empty. Has our solar system really passed the most important stage the formation of planets that we see everywhere in the Universe? In 2015, two of us (Konstantin Batygin and Gregory Laughlin) looked at how a tack change might affect a hypothetical group of super-Earths close to the Sun. Our conclusion was astonishing: super-Earths would not have survived the tack change. It is remarkable that the migrations of Jupiter in and out can explain many of the properties of the planets that we know, as well as those that are unknown.
As Jupiter plunged into the inner solar system, its bulldozing influence on the planetesimals would disrupt their neat circular orbits, turning them into a chaotic tangle of intersecting trajectories. Some planetesimals must have collided with great strength, breaking into fragments that inevitably gave rise to further collisions and destruction. Thus, Jupiter's inward migration likely triggered a cascade of impacts that destroyed the planetesimals, grinding them down to the size of boulders, pebbles, and sand.
Under the influence of collisional friction and aerodynamic drag in the gassed inner region of the protoplanetary disk, the destroyed planetesimals quickly lost their energy and spiraled closer to the Sun. During this fall, they could easily be captured in new resonances associated with any of the super-Earths close to them.
Thus, the tack change of Jupiter and Saturn may have caused a powerful attack on the population of the primordial inner planets of the solar system. As the former super-Earths fell into the Sun, they would have left behind a desolate region in the protoplanetary nebula, extending to orbital periods of about 100 days. As a result, Jupiter's rapid maneuver through the young Solar System led to the appearance of a rather narrow ring of rocky debris, from which the terrestrial planets formed hundreds of millions of years later. The confluence that led to this subtle choreography random events indicates that small, rocky planets like Earth—and perhaps even life on them—should be rare in the universe.
Nice model
By the time Jupiter and Saturn had moved back from their foray into inner part Solar system, the protoplanetary disk of gas and dust has already been greatly depleted. Eventually the resonant pair of Jupiter and Saturn came close to the newly formed Uranus and Neptune, and possibly another body of similar size. By using gravitational effects Braking in the gas dynamic duo captured these smaller giants in resonances. So when most of As gas escaped from the disk, the internal architecture of the Solar System likely consisted of a ring of rocky debris in the vicinity of Earth's current orbit.
In the outer region of the system there was a compact, resonant group of at least four giant planets moving in nearly circular orbits between the present orbit of Jupiter and about half the distance to the present orbit of Neptune. In the outer part of the disk, beyond the orbit of the outermost giant planet, at the far cold edge of the solar system, icy planetesimals moved. Over hundreds of millions of years, the terrestrial planets formed, and the once restless outer planets settled into a state that could be called stable. However, this has not happened yet the final stage evolution of the solar system.
The change of tack and the attack of Jupiter caused the last burst of interplanetary violence in the history of the Solar System, applied the final touch that brought the planetary retinue of our Sun almost to the configuration that we see today. This last episode, called the late heavy bombardment, occurred between 4.1 and 3.8 billion years ago, when the solar system temporarily turned into a shooting gallery. filled with many colliding planetesimals. Today, the scars from their impacts are visible as craters on the surface of the Moon.
Working with several colleagues at the Côte d'Azur Observatory in Nice in 2005, one of us (Alessandro Morbidelli) created the so-called Nice model to explain how the interactions between giant planets could have caused a late heavy bombardment. Where the tack ends, the Nice pattern begins.
The giant planets located close to each other were still moving in mutual resonance and still felt the weak gravitational influence of the outlying icy planetesimals. In fact, they were teetering on the brink of instability. Accumulating over millions of orbital revolutions over hundreds of millions of years, each individually insignificant influence of the outer planetesimals little by little changed the motion of the giants, slowly removing them from the delicate balance of resonances that connected them with each other. Crucial moment occurred when one of the giants fell out of resonance with the other, thereby disturbing the balance and launching a series of mutual chaotic disturbances of the planets, which shifted Jupiter slightly inward of the system, and the remaining giants outward. In a short time on a cosmic scale Over the course of several million years, the outer region of the Solar System experienced an abrupt transition from a tightly packed, nearly circular orbit to a diffuse and disordered configuration with planets moving in wide, elongated orbits. The interaction between the giant planets was so strong that one or even more of them may have been thrown far beyond the solar system into interstellar space.
If dynamic evolution stopped there, then the structure of the outer regions of the Solar System would correspond to the picture that we see in many exoplanetary systems, where giants move around their stars in eccentric orbits. Fortunately, the disk of icy planetesimals that had previously caused disorder in the motion of the giant planets later helped eliminate it by interacting with their elongated orbits. Passing close to Jupiter and other giant planets, planetesimals gradually took away their energy orbital movement and thereby rounded their orbits. At the same time, most of the planetesimals were ejected beyond gravitational influence Sun, but some remained in bound orbits, forming a disk of icy “junk” that we now call the Kuiper Belt.
Planet Nine: The Definitive Theory
Persistent observations at the largest telescopes are gradually revealing to us the vastness of the Kuiper Belt, demonstrating its unexpected structure. In particular, astronomers noticed a peculiar distribution of the most distant ones moving at the outer boundaries of the viewing area. Despite big difference distances from the Sun, the orbits of these objects are tightly grouped, as if they were all experiencing a common and very strong disturbance. Computer simulations by Batygin and Michael E. Brawn of the California Institute of Technology showed that such a picture could be created by a hitherto undetected object with a mass ten times greater than Earth, moving in a highly eccentric orbit around the Sun. with a period of about 20 thousand years. It is unlikely that such a planet could have formed so far away, but its appearance there can be quite easily understood if it was thrown there during the youth of the Solar System.
If the existence of the ninth planet is confirmed, this will sharply strengthen the restrictions on the picture of the evolution of our strange - with a “hole” in the center - Solar system and will put new demands on a theory that could explain all its features. Astronomers are now using largest telescopes Earth, trying to find this mysterious planet. Its discovery would complete the penultimate chapter in a long and complex history about how we tried to understand our place in the Universe. And this story will end only when we finally find planets with life orbiting other stars.
Just as DNA sequencing reveals the history of ancient human migrations across the surface of our small planet, computer modelling allows astronomers to reconstruct the majestic history of planetary travel over the billions of years in the life of the solar system. From its birth in a dark molecular cloud to the formation of the first planets, to the devastating events of tack changes, the attack of Jupiter and the Nice model, to the emergence of life and consciousness near at least one of the stars in the vastness Milky Way full biography our solar system will be one of the most significant achievements modern science- and undoubtedly one of the greatest stories ever told.
