A “red planet” surprised, a blow for the theory of the planet X?
Illustration of 2017 of201 (in medallion at the bottom right). © Mounting (Grok/Cheng et al, Arxiv 2025)
A team of astronomers, working in particular at Princeton University (United States), has just announced the discovery in the solar system of a new planet of the same type as Pluto. These scientists studied its orbit from data from 2011 to 2018 and were able to observe it for 13 nights.
Trajectory of the star from 2011 to 2018. The predicted trajectories perfectly agree with those observed for two weeks. © Cheng et al, 2025, Arxiv
Called 2017 of201, the star measures approximately 700 km in diameter, which allows it to enter the category of so -called dwarf planets, in the sense of Definition established by the International Astronomical Union In 2006. It belongs to transneptunian objects (or TNO), because located beyond the orbit of the planet Neptune. Its mass is estimated at 1/20,000 of that of the earth.
Probably frozen since located in the borders of the solar system, this dwarf planet has a very eccentric orbit, that is to say that it is very close to the sun and moves away just as much. Its perihelion, point closest to our star, is estimated at around 45 astronomical units (AU), more or less the distance from Pluto. His aphelia, where 2017 of201 sink the most into the Kuiper belt, ventures to more than 1600 AUs, an absolutely dizzying distance.
In addition, as the orbital speeds of the stars decrease with their distance from the star, this dwarf planet performs its complete orbit in approximately 25,000 years. Astronomers at the origin of this announcement believe that the star must have a very pronounced red color, like other Transneptunian bodies like Sedna.
Different shots of 2017 of201. © Cheng et al, 2025, Arxiv
This new dwarf planet has things to say about the solar system
Whatever the future that the nomenclature reserves in 2017 of201 (officially recognized in the same way as Pluto and Ceres, or in the anteroom of dwarf planets like other similar stars), its discovery is fascinating. Indeed, its existence could have strong implications on the past and the composition of the solar system.
First of all, the area of space where 2017 of201 was so far considered to be particularly empty and devoid of large stars. His discovery even had only 1 % chance of occurring, her orbit so eccentric making it practically undetectable 99 % of the time. Another very interesting aspect, 2017 of201 deviates considerably from the area in which this type of object is generally discovered, it should therefore have cousins and cousins not far.
Its extreme orbit could also explain as follows: “2017 of201 must have experienced close meetings with a giant planet, making it eject on a large orbit”indicates Eritas Yang of the Princeton and Co-author of the study Department of Astrophysical Sciences. “There may have been more than one stage in its migration. It is possible that this object was first ejected, then returned to the Oort cloud, the region most distant from our solar system, which houses many comets”in turn supposes Sihao Cheng of the Princeton Advanced Research Institute, the main author of the study.
And the planet X in all of this?
Nevertheless, 2017 of201 will not please everyone, because its presence makes the planet X more doubtful. Indeed, this supposed planet should have, at a time in the history of the solar system, eject our new dwarf planet candidate! For the authors, the presence of 2017 of201, as well as the high probability of a whole population of its fellow men, makes the existence of a massive X planet. And now legendary?
If the planet X existed, the most likely is that it should have ejecting 2017 of201. © Cheng et al, 2025, Arxiv
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