What is planet nine?

 Planet Nine Existence? something is moving

Finding something without knowing where to look  is not easy, and if it is not even certain that the thing exists it becomes even morecomplicated.Know it well Michael Brown and Konstantin Batygin,  two astronomers rather convinced that in  the extreme periphery of our solar system  is orbiting, never observed by anyone, a  planet at least twice the size of Earth. For years the two diehards argue that the  existence of this "ninth planet" would help to explain the strange similarities in  the orbits of some objects that orbit in the most remote part of our solar system. So far these are only theories and models of  celestial dynamics, discussed by an astronomical  consensus divided so far equally between enthusiasm and skepticism. So that for a long time  are alternating studies in favor and studies that instead want to demonstrate the inconsistency of  the evidence. The most recent one, published one  year ago, believes for example that the ambitious  hypothesis of Brown and Batygin is based on the  misunderstanding of a trivial statistical error. Let's see how things are going together. Will you? 

On February 18, 1930, the world became aware of  the discovery of what at that time was considered  "the ninth planet of the solar system", searched  for a long time by the young Clyde Tombaugh and finally found on the photographic plates  impressed by the fire of the 13-inch astrograph of the Lowell Observatory in Flagstaff, Arizona. After that momentous discovery, for a long time no one looked for other  objects orbiting beyond those remote distances. After all, almost no one believed that there  was something else to find since the planet found by Clyde Tombaugh seemed to account in  the best way of the alleged irregularities found in the movement of Uranus and Neptune. Over the years, it became increasingly clear that Pluto was not at all the massive planet  that was believed to be and began to get the idea that beyond the 40 astronomical units the  solar system hides much more than we could see. 

In 1992, a team of researchers led by American  astronomer Chad Trujillo announced the finding of the first transneptunian asteroid, establishing  the presence of a second asteroidal belt, stretching 15 times farther than the one now known  between Mars and Jupiter. A region that extends beyond Pluto for billions of kilometers and that  has taken the name "Kuiper belt" in honor of  Gerard Kuiper, the Dutch astronomer who in  the fifties had theorized the existence. 

The observations and discoveries that followed  over the years led astronomers to estimate that that huge reservoir of icy worlds could  contain hundreds of thousands of objects with  dimensions of hundreds of kilometers. So,  Pluto was no exception: there was a lot more going on out there at the edge of our  solar system. All you had to do was look.To take up the challenge in the early years  of this century was especially the astronomer at Caltech Michael Brown, who in a short time  discovered in that area also very large objects such as Quouar, Sedna, Orcus, Makemake, Haumea,  Gonggong... all planetoids with a diameter between 1000 and 2000 km. A string of successes  culminated in 2003 with the discovery of Eris:  a "planet" of the same size as Pluto. Paradoxically, it was precisely this crowding  of "planets" to decree in 2006 the downgrading  of Pluto and Eris to the rank of "Dwarf Planet". The decision, as you undoubtedly remember, was  taken after a turbulent debate that surprisingly saw the same Brown in the forefront in claiming  the need to redefine the concept of "planet", thus contributing to downgrade  not only Pluto but also his Eris! Since 2006 little else has been discovered  in the Kuiper belt... lots of objects with diameters around hundreds of kilometers,  but no other of semi-planetary size. 

The work of astronomers thus began to move  toward a statistical treatment of the different populations of objects in the Kuiper belt. Until, on January 20, 2016, Brown, along with one of his post-doc students,  Konstantin Batygin, presented a paper entitled "EVIDENCE FOR A DISTANT GIANT PLANET IN THE SOLAR  SYSTEM" in the pages of the Astronomical Journal. 

Batygin and Brown examine the orbital data of  Sedna and a small group of five other objects, observing that the primary axes of  their orbits are practically parallel; and, more critically, that the orbits  all have a very similar inclination. The bodies in the Kuiper Belt, including  Pluto, are all trans-Neptunian objects, with average distances from the Sun between 30  and 55 astronomical units. But the six objects studied by Batygin and Brown do not belong to the  Kuiper Belt. They are classified as ETNO (extreme trans-Neptunian objects) because  they have extremely elongated orbits. Even at perihelion, they are more than  30 astronomical units away from the Sun and at aphelion, they can reach - like Sedna -  distances close to one thousand astronomical units (1astronomical unit is equivalent to about  150 million kilometers and represents the average distance of the Earth from the Sun). Studying the orbits of these six ETNOs, Batygin and Brown noticed something strange. A feature  of their orbits, called the perihelion argument (basically the angular orientation  of the major semiaxis of the orbit), was similar in all six bodies. Also very similar  was the inclination of their orbital plane. In short, there was something, a force, that  seemed to act on the orbits of the six ETNO, orienting and stretching them all in the same way. The six bodies, by the way, had been discovered by six different telescopes during as many  different surveys, so it was to discard the hypothesis that their "grouping" in  orbiting around the Sun depended on a distortion due to the mode of observation. The two astronomers calculated that there was only a 0.007% probability that that  orbital disposition was casual; and after having conducted a series of simulations based  on different types of gravitational interactions,  they were convinced that the most  probable cause of the orbital similarity of the six ETNOs could only be the gravitational  attraction exerted on those bodies by a ninth planet of the solar system, very far from the Sun. Their simulations indicated that a planet with a  mass equal to about 10 Earth masses, was moving  along a very elongated orbit, distant on average 700 AU, but with a perihelion of 200 AU and an  aphelion of 1200 AU. located in an elliptical  orbit with an eccentricity of about 0.6, the  semi-major axis of 700 astronomical units, perihelion, and aphelion respectively at  200 and 1200 astronomical units from the Sun and perihelion argument opposite of 180° to  that of the six ETNO, could explain very well the orbital confinement of those six planets. After the publication of the study, debates flourished on the existence of the hypothetical  Planet Nine, but also intensified its research. A search conducted, however, almost blindly.  If this distant and cold body really existed, it would have an apparent magnitude greater  than 22, which means that we should try to perceive the movement of a bright dot  at least 600 times dimmer than Pluto... Over the years, thanks to increasingly  powerful and precise telescopes, astronomers have become quite adept at looking  for particular categories of celestial bodies: you indicate the features you want to the  instruments, to exclude everything else from the field of view, and then evaluate the results. In a way, though, it's like trawling, whereas in the case of the ninth  planet you'd need a... spear gun! Telescopes suitable and powerful  enough for the purpose are not many and are in high demand by researchers. Finding  vacancies is difficult, and astronomers are often reduced to having only a couple of  nights a year to pursue their observations.

In 2019, an additional study by Brown  and Batygin increased the number of  ETNOs with apparently aligned orbits to 14.  Which allowed the authors to refine their assessments of the characteristics  of the hypothetical planet nine: the average distance of 400-500 AU from the Sun. the distance at the perihelion of 280 AU distance at aphelion of 650 AU diameter of 25,000 km mass: 5 times that of the Earth orbit inclination of 20°.

Although the evidence brought by Batygin and  Brown seems quite convincing, no one really knows if Planet Nine exists or not. And until  we find out through direct observation, its existence will not be scientifically confirmed. But where could it be right now? For now,  no one really knows, although studies done so far  provide a rough idea of its motion in the sky and  its brightness. The current efforts of scientists  are focused on reducing the area of research: for example, new simulations of Batygin and  Brown have restricted the possible location of Planet Nine to an area of about 600 square  degrees (remember that the surface of the entire celestial sphere is about 40 thousand degrees!). Excluding the areas of the sky already monitored by automated surveys such as Pan STARRS  and WISE, the most reasonable conclusion is that Planet Nine could be close to its orbital  aphelion, at about 600 AU. Statistically, in fact, an object orbiting a star spends much more time  near its aphelion, where its velocity is lower. Its magnitude would then be +22: a brightness  within the reach of any professional telescope... but unfortunately, in the direction of the center  of the Milky Way. And if this rough prediction is true, it could be extremely complicated to  discover Planet Nine in front of the incredibly dense star fields near the center of our galaxy. In short... Between ups and downs, the scientific debate on the existence of  the ninth planet continues.  

A debate, sometimes made of very polemical  attacks, rekindled a year ago by new research published under the title No Evidence for Orbital  Clustering in the Extreme Trans-Neptunian Objects. According to the authors of the study, led by  Kevin Napier of the University of Michigan,  there would be nothing so strange in the orbits  of the 14 ETNOs mentioned by Brown and Batygin,  and their similarity could be just  the result of a statistical accident. Their thesis is that since these objects,  in addition to being few in number, are small and faint, very dark, and difficult  to spot except on rare, fortuitous occasions,  their apparent densification in a particular  region of the sky could be a function of the characteristics of the telescopic survey that  detected them, rather than the presence of a  "large attractor." It cannot be ruled out that  their distribution is actually uniform across the celestial vault...which would rule out the need  to bring up the existence of a perturbing planet. 

Of course, Brown and Batygin do not agree. And  their polemic vein in their reply can be seen in  Batygin's own words: "I'm still quite optimistic  about Planet Nine. If you see a bunch of bears to the east, you might think there was a bear cave  there. But Napier is saying the bears are all around us, because we haven't checked everywhere.  That logical jump is not one you can make."

Untangling this problem will require further  observations that lead to knowledge of an  increasing number of transneptunian  objects, to determine once and for all whether or not the accumulation that led  to the hypothesis of Planet Nine is there. The ninth planet will continue to keep  astronomers busy for a long time to come, but new data to settle their diatribe  could arrive within a few years. Because the planet is expected to be moving in  the northern celestial hemisphere, the primary search is for now being conducted with the Subaru  telescope at Mauna Kea, Hawaii, which has both an aperture large enough to see faint objects and  a wide field of view to shorten the search time. Then, in Chile, construction is underway on the  Vera Rubin Observatory, equipped with a powerful telescope (Large Synoptic Survey Telescope) that  will conduct observational campaigns to photograph  the night sky of the Southern Hemisphere.  It will allow precise mapping of objects in the Kuiper belt and will likely lead to the  discovery of many more transneptunian objects. U.S. astronomer Vera Rubin, after whom the new  telescope is named, was a pioneer in the study  of galaxy rotation and in defining "dark matter,"  the part that is invisible to us and is thought to occupy about 85 percent of the Universe.  Commenting on the complexity of his studies,he once said, "Many mysteries of the Universe  are still hidden from us. Their discovery awaits the adventurous scientists of the future." The  ninth planet is certainly one of these mysteries.

If you like my content and want more in the future please subscribe to my blog. I try to upload quite consistently.