Science

The solar system can once again have nine planets

Several studies and new discoveries suggest that it takes a planet 10 times larger than the Earth to explain the orbits of objects beyond Pluto.

Until recently, Pluto was at the frontier of the solar system. In schools all over the world the small planet was studied as the ninth of the family and beyond there seemed to be only the interstellar void. Things got complicated in the nineties with the discovery of a large number of small frozen objects in a region beyond Pluto which was christened the Kuiper Belt. The study of this area also showed that the one that for more than 70 years had been the ninth planet had more to do with the population of the new suburb. In 2006, in a controversial decision by the International Astronomical Union, Pluto was degraded and the solar system became eight planets, but the situation may soon change. In recent weeks, several scientific articles and some astronomical discoveries suggest that we are about to meet the new planet nine.

The suspicion that there is an unknown world beyond Pluto has a close link with the study of that belt that caused the degradation of the dwarf planet. In 2016, Konstantin Batygin and Michael Brown, of the Caltech Institute in California, published an article in which, from the analysis of the movements of these objects, they predicted the existence and certain characteristics of planet nine. It would have 10 times the mass of the Earth, it would need 15,000 years to give a turn to the Sun and in its moment of greater approach to our planet it would be 200 times farther than us from our star. Such a distant orbit would explain why we have not yet seen it.

On February 10, Batygin, Brown and two other colleagues published a review of all the data supporting the existence of the new planet and concluded that it is difficult to explain the movement of the frozen rocks of the Kuiper belt without the existence of a large planet that causes its strange movements. Brown, known for being one of the main responsible for relegating Pluto to the dwarf planet, believes that, with the available technology, the new planet should be detected in the next ten years or at least know better its probable orbit.

Another front in the search for the new planet of the solar system, which would be the first discovered since the nineteenth century and only the third since antiquity, is the search for new objects in the Kuiper belt that can expand indirect information about the unknown world. This research has so far been led by a trio of American astronomers. Scott Sheppard of the Carnegie Institution, David Tholen of the University of Hawaii, and Chad Trujillo of the University of Northern Arizona have discovered 80 percent of the new worlds in this distant region more than 9 billion kilometers from the Sun.

In December, this trio discovered Farout, a body three times farther from the Sun than Pluto, and in January they broke their own record by adding Farfarout to the catalogue. A few months earlier, in October, they had identified El Duende, a dwarf planet barely 300 kilometres in diameter, so eccentric that it takes 40,000 years to complete a return to the Sun. Its eccentricity, according to Shepard and his colleagues, could be explained by the presence of the ninth planet.

If it is finally located from its gravitational effects, it would join Neptune. In the 1840s there were still seven known planets of the solar system. The last discovered had been Uranus, in 1781, and despite the time elapsed, the astronomers had not been able to explain the irregularities of its orbit. This changed when mathematician Urbain Le Verrier analyzed their movements and deduced that there must be some other planet disturbing Uranus. Shortly after Le Verrier made his study public, astronomers in Germany used their calculations to locate Neptune exactly where the French predicted it would be.

Le Verrier’s prowess pushed other astronomers to try to make similar conjectures, but these kinds of searches have had resounding failures. In the 19th century, an anomaly in Mercury’s orbit was attempted with a planet called Vulcan, and in the 1980s, a brown dwarf star was proposed to be trapped by the Sun 1.5 light years away. Neither the planet nor the star has ever been found. Halfway between success and failure was the effort of Percival Lowell, who built an observatory in Arizona (USA) to look for planets beyond Neptune. The calculations on which he based his researches were erroneous, but from one of his telescopes was observed for the first time, in 1930, Pluto. It was not exactly what they were looking for, but it maintained its category of planet nine for more than seven decades.

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