Ninth planet

Early Assumptions (2014)

In 2014, astronomers Chadwick Trujillo and Scott Sheppard discovered ^[16] that some distant Kuiper belt objects have a perihelion argument close to zero. This means that they cross the ecliptic plane from south to north around the time of passage of the perihelion . Trujillo and Sheppard noticed that such a coincidence could be the result of one of the variants of the Lidov-Kozai effect , assuming that there is a massive planet in the Oort cloud . However, the Lidov – Kozai resonance did not explain why all the objects from the considered group cross the ecliptic plane at the perihelion in the same direction (from south to north) ^{[1] [2]} .

In the same year, Spanish astronomers from the University of Madrid confirmed that such a coincidence is unlikely and cannot be explained by ^[17] . They suggested the presence of super-earth with a mass of 10 M _⊕ at a distance of about 250 AU. and a more distant planet with a mass in the range from the mass of Mars to the mass of Uranus ^[17] . Later they suggested the existence of two large super-earths outside the orbit of Pluto, by computer modeling the dynamics of 7 trans-Neptune objects ( (90377) Sedna , (148209) 2000 CR105 , 2004 VN112 , 2007 TG422 , 2010 GB174 , 2012 VP113 , 2013 RF98 ) using the Monte method Carlo ^[18] .

Batygin and Brown (2016)

Batygin and Brown, trying to refute these hypotheses, on the contrary, noticed that all six isolated trans-Neptunian objects known for 2015 ( Sedny , 2012 VP ₁₁₃ , 2007 TG ₄₂₂ , 2004 VN ₁₁₂ , 2013 RF ₉₈ and 2010 GB ₁₇₄ ) have a semi-major axis of which more than 250 AU, not only the argument of perihelion practically coincides, but their orbits are oriented in space approximately the same. That is, they have a small spread in the longitude of the ascending node and the inclination of the orbit . By modeling, it was shown that the probability of such a coincidence is 0.007%, even taking into account observational selection. Such a coincidence is especially strange because the perihelion of celestial bodies shifts with time at different speeds. According to Michael Brown, this corresponds to the fact that you looked at a random moment at a watch with six hands moving at different speeds. And it turned out that they coincided. These observations allowed Michael Brown to estimate the probability of the real existence of the planet at 90% ^[19] .

Using the analytical perturbation theory and computer modeling, Batygin and Brown showed that such alignment of the orbits can be explained by the presence of one massive planet with a mass of the order of 10 M _⊕ , with a large semiaxis of about 400—1500 AU. and an eccentricity of the order of 0.5-0.8. In addition, this model of a shepherd planet made it possible to explain other features of the orbits of Kuiper belt objects. For example, why Sedna and 2012 VP ₁₃₃ , which never come close to Neptune , have such a large eccentricity . Moreover, this model predicts that there are objects in the Kuiper belt with orbits perpendicular to the plane of the ecliptic. In recent years, several such objects have been found: 2013 BL ₇₆ , 2012 DR ₃₀ , 2010 BK ₁₁₈ , 2010 NV ₁ , 2009 MS ₉ , 2008 KV ₄₂ . The hypothesis of the existence of the Ninth Planet satisfies the Popper criterion , that is, it leads to predictions that can be verified regardless of direct observation of this planet ^{[1] [20] [21]} .

In the Solar System

The formation of the Ninth Planet depended on its structure. If it looks like a gas planet , then, according to the most realistic theory at the moment ^[22] , this means that it was building up a gas shell on a solid rocky core. In another case, if this planet is super-earth , then it, like other planets of the earth group, was sticking together from small fragments, asteroids and planetesimals , gradually gaining mass ^[23] .

But there is one problem: according to Brown and Batygin, the Solar Nebula must be "too exceptional for the planet to form in such a distant and eccentric orbit", and they believe that it formed closer to the Sun, and then was thrown out by Jupiter or Saturn in time of the nebular era ^[1] to the outer edges of the solar system , according to a mechanism reminiscent of the ejection of the fifth giant planet in the latest versions of the Nice model . According to Batygin’s current estimates, this could have occurred between three and ten million years after the formation of the Solar System ^[24] and did not affect the late heavy bombardment, which, according to Batygin ^[25] , would require a different explanation ^[26] .

It can be direct confirmation of modeling the history of the movement of planetary orbits in the Solar System ^[27] , including the unresolved migration problem of Jupiter, which, according to the simulation results, should have reached a stable orbit much closer to the Sun ^[28] . According to computer simulations of David Nesvorny from the Southwest Research Institute in Boulder (USA) and Alessandro Morbidelli from the Cote d'Azur Observatory (France), with the addition of the fifth gas giant, the chance of the formation of the present-day solar system increases by more than 20 times ^[29] compared with the situation without it and with a large number of planetesimals ^[30] .

According to this theory, Jupiter was supposed to gradually move inside the solar system - he could return to modern orbit only in a jump, pushing a rather massive object from the orbit of the Sun. But since Uranus and Neptune are still in circular and stable orbits , they could not serve as an impetus for Jupiter. Consequently, he had to throw away a previously unknown planet, which, judging by the elongation of the orbit, could be the Ninth Planet. However, according to the Nesvorny model, the fifth giant planet was ejected from the solar system forever ^[31] .

If Jupiter threw the Ninth Planet into an elongated orbit at a fairly early stage of planetary migration, you can find out additional facts about the history of the solar system. In particular, in early March 2016, a group of scientists from the Harvard-Smithsonian Center for Astrophysics and the University of Michigan, based on Monte Carlo simulations, suggested that over the 4.5 billion years of the existence and development of the solar system there was a 10-15 percent chance of the departure of the Ninth Planet beyond the limits of the solar system, provided that another star is passing close. This means that in the entire history of the planetary system, it itself has not come close enough to massive objects ^[32] .

As an exoplanet

Alexander Mastill, along with astronomers from Lund and Bordeaux, by computer simulation showed that the Ninth Planet could form in another star system , and when it passed near the Solar, change its parent star to the Sun. The study was published in Monthly Notices of the Royal Astronomical Society Letters .

Alexander Mastill, astronomer from Lund University :

The irony is that astronomers usually find exoplanets hundreds of light years from us in other solar systems, and here one of them can hide in our backyard.

This assumption may be true if the Ninth Planet was captured by the Sun in the early moments of the formation of the Solar System , when the stars had not yet had time to move away from each other after their formation in the nebula . At that time, a star passing close enough might not have enough gravity to keep the planet in its orbit , and it switched to a more eccentric orbit to the young Sun ^[33] :

Other planets could push the ninth planet, and when it was in orbit, which was too elongated with respect to the star, our sun took the opportunity to steal and capture the ninth planet from another star. When the Sun later left the star cluster in which it was born, the Ninth Planet has already remained in the orbit of our star.

However, such a scenario requires the fulfillment of several conditions that were used in computer simulation ^[34] :

• stars in a cluster move at low speeds (about 1 km / s);
• The sun should pass near the parent star of the Ninth Planet about 150 AU to avoid disturbances in the Kuiper belt ;
• so that the gravity of the Sun can overcome the gravity of the parent star, the Ninth planet must be in orbit with a radius of about 100 AU;
• after the capture of the exoplanet by the Sun, it is possible to approximately reproduce the current dynamic configuration of the solar system.

Orbit

Brown and Batygin calculations

It is assumed that the planet is about 20 times farther from the Sun than Neptune (30 AU), i.e. an average of 600 AU , and makes a revolution around the Sun for 10,000 - 20,000 years. However, due to the large eccentricity of the elliptical orbit, it can move away and approach the Sun at distances from 1200 AU up to 200 au ^{[40] [41]} Its orbit is supposedly inclined to the ecliptic by 30 ° ^[20] . However, it must be borne in mind that the above parameters are those that were used in modeling the position of distant objects in the Kuiper belt. They show only an approximate order of the possible true parameters of the orbit of the Ninth Planet ^[1] .

Resonance refinement

First Study

Scientists at Arizona University , including Prof. , Dr. Catherine Wolf and Van Xiangyu, in their article ^[42] on arXiv.org suggested that if the Ninth Planet did intersect with certain highly eccentric Kuiper belt objects, then the chances are good that it is in orbital resonance with these objects.

In an email to Universe Today, Renu Malhotra, Catherine Wolf and Wang Xianyu wrote :

The objects of the Kuiper belt, which we investigated in our work, are different from others because they have very distant and very elongated orbits, but their closest approach to the Sun is not close enough to be significantly affected by Neptune. Thus, we have six of these objects, whose orbits are slightly affected by the known planets of our solar system. But if only a few hundred a. e. from the Sun there was another planet, until it was discovered, it would affect six of these objects. <...> Unusual objects of the Kuiper belt are not massive enough to be in resonance with each other, but the fact that their orbital periods fall in the region of simple relations can mean that they are in resonance with a massive invisible object.

After analyzing the characteristics of the orbits of isolated trans-Neptune objects , whose orbits had a major semi-axis of more than 150 AU, scientists came to the conclusion that these objects can have a resonance with the Ninth planet.

According to the data obtained in the calculations, the period of revolution of the Ninth planet around the Sun, which is equal to 17 117 Earth years, as well as the major axis of the orbit , which is now equal to 665 AU , were specified . These data are consistent with the estimates of Brown and Batygin, that is, for the period of rotation around the Sun , they range from 10,000 to 20,000 , and for the semi-major axis it is approximately 700 AU Also, these data suggest that the Ninth Planet has an orbital inclination relative to the ecliptic either 18 ° at an ascending node longitude of 101 ° (as the average inclination of the objects under study), or 48 ° at an ascending node longitude of −5 ° ^[43] .

However, according to scientists, it is impossible to say with full confidence about the detection of resonances: ^{[44] [45]}

There are quite a lot of uncertainties. The orbits of these extreme objects of the Kuiper belt are not very well known, since they move very slowly in the sky, and we observe only a small part of their orbital motion. So their orbital periods may differ from current estimates, and some of them may come out of resonance with a hypothetical planet. There is also the possibility that the orbital periods of these objects are related; so far we have observed not so many similar objects and have limited data.

Second Study

On December 23, 2016, astronomers from Yale University in the United States clarified the parameters of the Ninth Planet by re-examining the resonances of isolated TNOs based on computer simulation by the Monte Carlo method , which made it possible to track the evolution of the solar system to its current state. According to the data obtained, the major axis of the orbit are 654 astronomical units, the eccentricity is 0.45, and the inclination of the orbit is 30 degrees. It also follows from the work that the mass of the Ninth Planet was estimated at 6–12 M _⊕ ^[46] .

Results

Physical Characteristics

Brown and Batygin calculations

The planet supposedly has a radius of 2-4 R _⊕ and a mass of about 10 M _⊕ , which puts it in this indicator between the planets of the earth group and the giant planets .

This mass is enough for the planet to be able to clear its orbit from other objects. Thus, this is a real super-earth , unlike dwarf , after the discovery of which by Michael Brown, Pluto was deprived of the status of a planet . Moreover, this planet dominates the region, which is larger than that of any other known planet of the solar system ^[20] .

It has been suggested that this planet is a gas (dense gas-ice) giant , looks like Neptune and has a similar albedo ^[48] .

Clarification by physicists at the University of Bern

Physicists Christoph Mordasini and his graduate student Esther Linder from the University of Bern in Switzerland published an article in Astronomy & Astrophysics that suggested what the Ninth Planet might look like. The purpose of the simulation was to find out a rough estimate of the radius , temperature , brightness and level of thermal radiation of the planet. The last parameter is the most important of these, since the Ninth Planet may be too dim for modern telescopes, but its thermal signature can be calculated by other means. According to the simulation, it amounted to only 0.006 of Jupiter's own luminosity. Scientists have modeled the options for cooling and compressing planets with masses of 5, 10, 15 and 20 M _⊕ at a distance of 280, 700 and 1120 AU respectively.

In the article, scientists abandoned the version that the planet was previously an exoplanet that the sun captured from a neighboring star, and modeled its structure as part of evolution within the solar system . According to researchers, the planet is a substantially reduced copy of the ice giants Uranus and Neptune and is surrounded by an atmosphere of hydrogen and helium. The radius of the Ninth Planet with ten earth masses is only 3.66 times larger than the earth and is approximately 23,000 km, and its temperature is 47 Kelvin, which is approximately −226 degrees Celsius ^[49] .

Clarification by physicists from Konkoy Observatory

^[50]

Clarification of orbital and physical characteristics (2019)

The authors of a scientific paper published in the journal Physics Reports clarified that the Ninth Planet has a mass equal to five masses of the Earth, the major semi-axis of its orbit is 400 AU, it makes a revolution around the Sun in about 10 thousand years ^[51] .

Direct observation

Currently, the existence of a planet is only a hypothesis. It can be confirmed by visual detection.

In contrast to the discovery of Neptune , which was made on the basis of the deviation of Uranus from movement according to Kepler’s laws , the existence of the Ninth Planet is manifested in statistical anomalies of the orbits of small planets that have developed over billions of years. This method allows you to calculate the estimated parameters of the planet’s orbit, but does not even determine approximately where the planet’s orbit is currently located. Along with the fact that the planet moves very slowly (the orbital period can be from 10 to 20 thousand years) and is far from the Earth (the apparent magnitude can be more than 22), this leads to the fact that its search can be very difficult ^{[ 53]} .

To search for the planet, Brown and Batygin reserved time on the Japanese Subaru telescope at the observatory in Hawaii. Sheppard and Trujillo joined the search. According to Brown, an examination of most of the sky where the planet may be located will take about five years ^{[41] [54]} .

Rechecking data

There is a possibility that the Ninth Planet was already recorded on the photographs of some telescopes, and its photographs are in the archives, but because of its dullness and slow movement against the background of distant stationary objects, it was not noticed ^[55] .

For this reason, in February 2017, NASA launched the Backyard Worlds: Planet 9 project, where participants are encouraged to search for moving objects among animated images taken by the WISE telescope in 2010-2011. Among them, the Ninth Planet can be seen, however, at the same time, the discovery of new brown dwarfs is also possible ^{[56] [57]} .

Evidence based on the orbits of isolated TNOs

The model predicts that in addition to the objects with a large eccentricity (which led to the hypothesis of the existence of the Ninth Planet), there should be a population of related objects with a small eccentricity, in which the perihelion is grouped at a point opposite the perihelion of the considered group. The search for such objects is one of the main methods that can confirm or refute this hypothesis ^[1] . Later, on August 30, 2016, the opening of one such facility was announced ( 2013 FT ₂₈ ).

Since the theory of Michael Brown and Konstantin Batygin is based on isolated TNOs, the search for such objects also increases the chances of the existence of the Ninth Planet. In a study published in The Astronomical Journal , Chadwick Trujillo and Scott Sheppard talk about the discovery of three new extreme trans-Neptune objects in the Kuiper belt ( 2013 FT ₂₈ , 2014 FE ₇₂ , 2014 SR ₃₄₉ ) using the Dark Energy Camera tool on a 4-meter telescope Victor Blanco in Chile and the Japanese Hyper Suprime-Camera instrument on the 8-meter Subaru telescope in Hawaii ^[58] . At object 2013 FT _{28, the} perihelion is directed in the opposite direction from all other extreme TNOs. 2014 FE ₇₂ and 2014 SR ₃₄₉ have a similar perihelion orientation to other isolated trans-Neptune objects .

Also in 2016, it became known that there was a separate trans-Neptune object uo3L91 ^[59] . Its longitude of the ascending node approximately corresponded to the average value of all other isolated TNOs. It is a trans-Neptune object with the largest perihelion. The opening was officially announced on April 6, 2017, then it was given the official name 2013 SY ₉₉ ^[60]

In October 2016, Batygin and Brown made another prediction, which was revealed during a more detailed simulation. All isolated TNOs must have a systematic distribution in the inclination of the orbital planes. This model was built on the basis of six original objects, and if each next perpendicular plane (north pole) of the orbit is located in accordance with the prediction, this will significantly strengthen the reliability of the theory. As it turned out, all new isolated TNOs fit perfectly into the model ^{[61] [62]} .

For objects 2008 ST ₂₉₁ , 2015 RR ₂₄₅ , 2014 FE ₇₂ and 2014 UZ _{224, the} orbit lies completely beyond the orbit of Neptune ^[63] . Object 2016 NM ₅₆ moves in a retrograde orbit , since its inclination is 144.04789 ° ^[64] .

In October 2018, the discovery of another minor planet 2015 TG ₃₈₇ (Goblin) was announced, which also confirms the hypothesis of the existence of the Ninth Planet ^[65] .

The table below summarizes the characteristics of all known isolated trans-Neptune objects . In this case, only those that approach the Sun no closer than 30 a. e. and the semiaxis of which is 250 a. e .. In 2015, six such cases were known, in 2016 there were already nine. In 2017 , another was opened. The green color indicates the isolated TNOs that were known at the end of 2015 and were used in the original work of Michael Brown and Konstantin Batygin ^[1] . Blue color marks new objects whose discoveries were published after writing this work.

Criticism

Antranik Sefilian of the University of Cambridge and Jihad Touma of the American University of Beirut calculated that the unusual orbits of some trans-Neptune objects are explained by the influence of gravity not on the ninth planet, but on small objects that make up the disk outside the orbit of Neptune ^{[70] [ 71]} .

Other evidence

By Influence on the Solar System

At the end of February 2016, French astronomers wrote to The Guardian that, having analyzed data from the Cassini spacecraft, they were able to exclude two large zones, reducing the search area of ​​the Ninth Planet by a total of 50%. Using computer simulation , a group of scientists calculated what effect the Ninth Planet should have on gas giants , and then studied their trajectory in the Solar System . According to the results of the study, the possibility of finding the Ninth Planet in perihelion (since it would affect other planets) and about halfway from it is excluded. The most probable region of its location was the region of the orbit halfway to the aphelion ^[72] .

By the shift of the axis of rotation of the Sun

All the planets of the solar system have a small spread (several degrees) relative to the ecliptic , however, the axis of rotation of the sun is tilted by 6 °. If we take into account the generally accepted theory of planet formation , it turns out that the rotation of the star, and not the rest of the disk, is wrong.

Michael Brown :

This is such a deep-seated mystery, and it is so difficult to explain that people simply don’t talk about it.

In October 2016, in one of the publications of the Astrophysical Journal, Michael Brown and Konstantin Batygin suggested that the angular momentum of the Ninth Planet swings the Solar System due to the large inclination relative to the ecliptic . According to their calculations, the six-degree tilt of the Sun is ideally consistent with the theory of the Ninth Planet ^[73] .

Title

The Ninth Planet does not have an official name, and it will not be until its existence is confirmed, it is highly desirable - visual detection. After confirmation, the International Astronomical Union will have to give the Ninth Planet an official name. Priority is usually given to the option proposed by the discoverers ^[74] . Most likely, the name will be chosen from the names of Roman or Greek mythology. ^[75] .

In their first work, Batygin and Brown called the Ninth Planet simply “disturbing the order” ( French perturber ) ^[1] , and the name “Ninth Planet” first appeared only in the following articles ^[76] . They refused to give a name to the alleged planet, believing that it is better to entrust it to the “world community” ^[77] . Despite this, they call the Ninth Planet Fatty ( Eng. Fatty ), as well as Jehoshaphat ( Eng. Jehoshaphat ) or George ( Eng. George ). ^[3]

Commenting

Batygin shows some caution in interpreting the results of modeling carried out in their joint scientific work with Michael Brown: “Until the Ninth Planet is fixed to the camera, it is not considered real. All we now know is an echo ” ^[78] . Brown estimated the chances of the Ninth Planet to be 90% ^[4] . Gregory Laughlin , one of the few researchers who knew about this article in advance, gives an estimate of the probability of its existence 68.3% ^[3] . Other skeptical scientists require more data in terms of finding new TNOs to be analyzed or final photographic confirmation ^{[79] [80] [81]} . Vladimir Surdin , a senior fellow at the Sternberg State Astronomical Institute of Moscow State University, referring to the WISE orbiting telescope , which examined the periphery of the solar system in the infrared and is potentially capable of detecting this planet, but still not detecting it, suggests that this planet is most likely giant does not exist ^[82] . The astronomer Ethan Siegel from Lewis and Clark College in Portland (USA) also believes ^[83] . A similar opinion is shared by David Jewitt , an American astronomer who made a great contribution to the discovery of the Kuiper belt . He argues that the magnitude of the statistical significance of 3.8 sigma, obtained by Batygin and Brown, deserves further consideration, but he knows many cases where results with similar significance were not confirmed. Also, of the dozen objects discovered by Trujillo and Sheppard, only six were selected, which, according to Juitt, indicates some bias in the analysis ^[41] . Brown, recognizing the validity of a skeptical point of view, believes that the available data is enough to search for a new planet ^{[79] [80] [81]} .

Jim Green, director of NASA's Planetary Sciences Division, supports Brown by saying that “evidence is stronger now than ever before.” ^[84] But Green also warned of the possibility of other explanations for the observed movement of remote TNOs, and, quoting Karl Sagan , he said that “extraordinary statements require extraordinary evidence” ^[4] .

After computer modeling, Anne-Marie Madigan from the Department of Astrophysical and Planetary Sciences, together with her colleagues, came to the conclusion that the strange orbits of isolated trans-Neptune objects can be explained not by the Ninth Planet, but by collective gravity, since smaller objects moving from the side of the Sun crash into more large objects of the Sedna type, as a result of which larger objects are repelled to the outskirts of the Solar system and the parameters of their orbits change ^{[85] [86]} .

In society

As with other important scientific discoveries, some media associate the assumption of the Ninth Planet with the approaching end of the world , including the planet Nibiru , which should collide with the Earth ^[87] . These assumptions are not considered due to the lack of substantiation ^[88] .

Also, the ninth planet is added to Universe Sandbox 2 .

• Planets beyond the orbit of Neptune ( Planet X )
• Tyuche (hypothetical planet)

• The Fifth Gas Giant Hypothesis
• Pluto

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