In the role of the ninth planet of the solar system - vacated by Pluto since its demotion to the rank of "dwarf" in August 2006 - the candidates follow one another but are not alike... While the existence of the hypothetical planet nine postulated in 2016 by American astronomers Mike Brown and Konstantin Batyguine is now proving less and less probable, two Japanese researchers in turn suggest the existence of a hidden planet well beyond the orbit of Neptune, in what astronomers call the Kuiper belt.
This area of our planetary system, which is located at a distance from our star of between 30 and 55 astronomical units (AU) – approximately 30 to 55 times the Earth-Sun distance – is populated by icy rocks and dwarf planets such as Pluto, Ceres, Eris, Hauméa and Makemaké.
It is also the study of the orbits of some of these small bodies that scientists call trans-Neptunian objects (TNO), which suggests that the gravity exerted by an unknown planet disrupts their celestial courses. Because it is indeed on mathematical calculations and not on any detection that the work of Patryk Sofia Lykawka of Kindai University in Japan and Takashi Ito of the National Astronomical Observatory of Japan, recently published in The Astronomical Journal, is based. . This in no way reduces their interest since this is how Urbain Le Verrier, in his time, discovered the planet Neptune based on its gravitational influence on Uranus.
But back to this new hypothetical ninth planet. By carefully examining how trans-Neptunian objects behave, the two astronomers determined several of its characteristics. According to their calculations, it should be 1.5 to 3 times the mass of the Earth and would evolve between 200 and 500 astronomical units (AU) from the Sun (or approximately 200 to 500 times the Earth-Moon distance). As for its orbit, it would be inclined by approximately 30 degrees relative to the ecliptic plane in which our planet orbits the Sun. It is therefore a very different planet from that envisaged by Batyguine and Brown, both larger (5 to 10 Earth masses) and more distant (between 200 and 1,000 AU).