The ninth planet - is there more to our solarsystem ?

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (and Pluto). These are the eight planets of our solarsystem that everyone knows, but there might be anotherone.

Search for Planet 9

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Are there already 9 planets? Right. Not quite. Pluto was "degraded" to the dwarf planet in 2006 because the term "planet" was redefined, since meanwhile several celestial objects have been found that have the same mass and size as Pluto. Since then, astronomers have assumed that our solar system has only 8 planets.

In recent years, however, more and more asteroids and dwarf planets with very eccentric elliptical orbits have been observed, which cannot be explained beyond the Kuiper belt without a larger source of gravity. In 2016 Konstantin Batygin and Michael E. Brown published a research paper in which they explained these phenomena with a 9th planet, this planet is said to be the sun at a distance of around 700 AU (700 times the distance from the sun <-> earth and 20 times the distance Orbit <-> Neptune), be around 10 earth masses, have a radius 2-4 times larger than the earth and have a solar orbital period of 10-20 thousand earth years. This additional celestial body could also explain how the unstable orbit of the 4 inner planets could survive the initial phase of the solar system. The inclination of the sun's axis of rotation could also be explained with the help of this planet. But how do you find a planet that's so far out in space? After all, because it is so far away, it hardly reflects any radiation, whether in the infrared range (heat) or in the visual range (light). You can measure this radiation on Earth, which was done in 2010 - 2011 with the space telescope "Wise", but data analysis can only be done by humans, since computer programs are not reliable asteroids and dwarf planets, from brown dwarfs (= stars that are too easy for are a nuclear fusion and therefore can only radiate in the infrared range) or distinguish a possible planet 9. The amount of data is also far too large for a handful of scientists, which is why the "Backyard Worlds: Planet 9" program was launched, for which amateur astronomers can be found on the website https://www.zooniverse.org/projects/marckuchner/backyard-worlds -planet-9 get access to the data from the telescope and can search for the planet and other undiscovered objects (such as brown dwarfs) that lie between us and Alpha Centauri. As a reward, there is a mention of being a co-discoverer of the planet. The TESS space telescope could have "accidentally" discovered Planet 9, the telescope is actually supposed to be looking for extrasolar short exoplanets, but it has already been able to discover several asteroids and dwarf planets with the same brightness as Planet 9 probably did. However, there is also an incredibly large amount of data and hardly any possibilities to search it completely. So there remains a search for the needle in the haystack.

But why is it so difficult to specifically search for a single planet in our solar system, whereas we can find planets in rows in other solar systems millions of light years away and in some cases even determine how large they are, what their atmosphere is made of and whether are they habitable?

The problem lies in the perspective, while we look up at other solar systems from “outside” and, among other things, the Doppler effect, the microlens effect or transit effects cannot work in our solar system because "Planet 9" cannot lie between us and the sun.