Two dwarf planets beyond Pluto in our solar system?

At least two unknown dwarf planets may be hiding in our solar system beyond Pluto, a new study suggests.
According to calculations by scientists at the Complutense University of Madrid (UCM, Spain) and the University of Cambridge (UK) not one, but at least two planets must exist to explain the orbital behaviour of extreme trans-Neptunian objects (ETNO).
The most accepted theory establishes that the orbits of these objects, which travel beyond Neptune, should be distributed randomly, and by an observational bias, their paths must fulfil a series of characteristics: have a semi-major axis with a value close to 150 AU (astronomical units or times the distance between the Earth and the Sun), an inclination of almost 0 degrees and an argument or angle of perihelion (closest point of the orbit to our Sun) also close to 0 degrees or 180 degrees.

Yet what is observed in a dozen of these bodies is quite different: the values of the semi-major axis are very disperse (between 150 AU and 525 AU), the average inclination of their orbit is around 20 degrees and argument of Perihelion -31 degrees, without appearing in any case close to 180 degrees.
"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNO and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto," said Carlos de la Fuente Marcos, scientist at the UCM and co-author of the study.

"The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system," he said.
To carry out the study, published as two articles in the journal Monthly Notices of the Royal Astronomical Society Letters, the researchers have analysed the effects of the so-called 'Kozai mechanism', related to the gravitational perturbation that a large body exerts on the orbit of another much smaller and further away object.
As a reference they have considered how this mechanism works in the case of comet 96P/Machholz1 under the influence of Jupiter.