American scientists have come to the conclusion that the potential ninth planet of the solar system, known as planet X, is 5-10 times heavier than Earth, that is, it belongs to the class of super-earths, and not gas giants, as previously thought. The astronomers' research is aimed at publication in the journal Physics Reports and is available in the arXiv.org electronic preprint library.
Analysis of the motion of trans-Neptunian celestial bodies showed that planet X is about one and a half times closer to the Sun than previously thought. Scientists believe that the potential ninth planet is in orbit with a semi-major axis of 400-800 astronomical units and an inclination of 15-25 degrees. Eccentricity (characterizes the degree of elongation of the orbit) is estimated at 0.2-0.5.
The study was attended by Michael Brown and Konstantin Batygin of the California Institute of Technology (Pasadena, USA), who reported in January 2016 that a Neptune-sized object 10 times heavier than Earth was found outside Pluto's orbit.
In June 2017, astronomers from the University of Arizona (USA) admitted the existence of a 10th planet in the solar system, comparable in size and mass to Mars.
In March 2016, astronomers from Sweden and France suggested that Planet X may have previously been an exoplanet that the Sun has captured from a nearby star.
There are currently eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.