perihelion of roughly 80 AU, which led them to suggest that it offered evidence of a potential trans-Neptunian planet. Trujillo and Sheppard argued that the orbital clustering of arguments of perihelia for and other extremely distant TNOs suggests the existence of a "super-Earth" of between 2 and 15 Earth masses beyond 200 AU and possibly on an inclined orbit at 1,500 AU. In 2014 astronomers at the Universidad Complutense in Madrid suggested that the available data actually indicates more than one trans-Neptunian planet; subsequent work further suggests that the evidence is robust enough but rather than connected with Ω and ω, semi-major axes and nodal distances could be the signposts. Additional work based on improved orbits of 39 objects still indicates that more than one perturber could be present and that one of them could orbit the Sun at 300-400 AU. Further analysis and Planet Nine hypothesis On January 20, 2016, Brown and Konstantin Batygin published an article corroborating Trujillo and Sheppard's initial findings; proposing a super-Earth (dubbed Planet Nine) based on a statistical clustering of the arguments of perihelia (noted before) near zero and also ascending nodes near 113° of six distant trans-Neptunian objects. They estimated it to be ten times the mass of Earth (about 60% the mass of Neptune) with a semimajor axis of approximately 400–1500 AU. Probability Even without gravitational evidence, Mike Brown, the discoverer of Sedna, has argued that Sedna's 12,000-year orbit means that probability alone suggests that an Earth-sized object exists beyond Neptune. Sedna's orbit is so eccentric that it spends only a small fraction of its orbital period near the Sun, where it can be easily observed. This means that unless its discovery was a freak accident, there is probably a substantial population of objects roughly Sedna's diameter yet to be observed in its orbital region. Mike Brown noted that However, Brown notes that even though it might approach or exceed Earth in size, should such an object be found it would still be a "dwarf planet" by the current definition, because it would not have cleared its neighbourhood sufficiently. Kuiper cliff and "Planet Ten" Additionally, speculation of a possible trans-Neptunian planet has revolved around the so-called "Kuiper cliff". The Kuiper belt terminates suddenly at a distance of from the Sun. Brunini and Melita have speculated that this sudden drop-off may be attributed to the presence of an object with a mass between