Kuiper belt: Planet X: a new member of the Solar System club? | United States

Paraphrasing Rutger Hauer’s soliloquy at the end of Ridley Scott’s 1982 sci-fi classic Blade runner, we can say, and it would be true, that we saw things that we would not believe: bodies of ice beyond the orbit of Neptune, dwarf planets, objects that move with orbits elongated, orbital planets which display the same angle of inclination, perihelions which extend beyond the gravitational influence of Neptune… but all this information will not be lost in time, like tears in the rain. And now, the time has come to understand what exactly is going on with Planet 9 or Planet X.

From childhood, we are sensitized and devote songs to the architecture of our largest home, the solar system: a star surrounded by eight planets, the closest to the Sun, Mercury, and the furthest, Neptune. The majority of the planets (with the exception of Uranus and Neptune) were known to science in antiquity and in this sense we have made little progress since the invention of the telescope. In recent years, however, we have discovered a series of huge rock objects beyond Neptune which we have grouped together as Trans-Neptunian Objects, also known as the Kuiper Belt in honor. by astronomer Gerard Kuiper, who predicted its existence. in 1951. The belt is made up of thousands of icy bodies, the majority of which are smaller than Texas (if three-dimensional) and which are, literally, the debris of the formation of the solar system. The Kuiper Belt contains a few very well-known objects: one is Pluto, the other is Arrokoth (which means sky or cloud in the Powhatan language), formerly known as Ultima Thule, and the most distant object studied. in space by a spaceship. to date when New Horizons flew on January 1, 2019.

Planet X would be a large planet with a mass between five and 10 times that of Earth

Most objects in the Kuiper Belt move as one would expect due to the mutual gravitational influence generated by the presence of the eight planets and the Sun. Until then, everything is in order. However, a problem arises because since 2004 a series of objects have been identified performing particular movements in this area of ​​the solar system. It’s like watching a swing moving in a tree with no one sitting on it: we know someone has to push it. These “strange” movements gave rise to a thesis, put forward in 2016, of the existence of an additional planet beyond the orbit of Neptune which has not yet been detected. This potential planet has become colloquially known as Planet 9 or Planet X.

This is not the first time that the abnormal orbital behavior of known objects has led to a new discovery. Nor will it be the first time that it has only resulted in an improved review of measures. But since we have news that tells us failures every day, let’s focus on a success story that began with William Herschel’s discovery in 1781 of a new member of the solar system, Uranus. The newly discovered planet had a long orbit – 84 years – and within 60 years of the Herschel Telescope landing on it, enthusiastic astronomers set out to calculate its ephemeris (a table of values ​​that provides the position astrological objects in the sky at a given time), depending on the positions of the planets known up to that point.

The problem was that the calculations and observations did not match, which led the French mathematician Urbain Le Verrier to propose, in 1846, the existence of another planet further away to explain the differences. The planet causing these anomalies was discovered the same year, very close to its predicted position, and was named Neptune.

With the mathematical discovery of Neptune, we were on a roll, and the unexplained movements of objects in the solar system continued to inspire predictions of the existence, and often the location, of other objects in our immediate vicinity. As such, and despite the addition of Neptune to the calculations, small deviations in the observed and calculated orbits of the giant planets remained, leading to the search for Planet X and the construction of the Lowell Observatory in Arizona, this which ultimately led to the discovery of Pluto.

Pluto was downgraded to a dwarf planet in 2006 and, going back to current history, it had considerably less mass – about 3,200 times less – than the wanted planet X. Finally, the revised measurements of Neptune’s size provided by the Traveler 2 The probe unraveled the gaps in the orbits of giant planets and eliminated the need for a massive additional body within the confines of the solar system. Until a few years ago.

These “strange” movements of objects in the Kupier belt gave rise to a thesis of the existence of an additional planet beyond the orbit of Neptune.

In recent years, data has been compiled on particular orbital models in some objects beyond the orbital sphere of Neptune. These are bodies that move with elongated orbits, in ellipses oriented in the same direction, on plains tilted at the same angle and with orbits, in some cases, that go in the opposite direction to normal. This is not explained by the influence of the massive bodies that we know of and suggests the possible existence of a planet that we have not yet seen but which is between 300 and 800 times farther from the Sun than it is. is Earth. It would be a large planet with a mass between five and 10 times greater than ours, with a moderately tilted (15-20 degrees) and elongated orbit. Above all, it would be a planet that will be very difficult – but not impossible – to detect over the next decade and whose process of formation, due to the great distance that separates it from the Sun, also poses a formidable problem. .

It is in this population of scattered debris, scattered between the orbit of Neptune and the confines of the solar system – the heliosphere – where at this moment, like the devil in detail, the history of the solar system, its dynamic evolution and maybe a new planet are hidden. As is so often the case in life, it’s not uncommon for us not to find something that could be, perhaps literally, right under our noses.

Eva villaver is an astrophysicist and researcher at the Spanish Center for Astrobiology, part of the Spanish National Research Council and the National Institute of Aerospace Technology (CAB / CSIC-INTA).

English version by Rob Train.