In addition to the eight planets (excluding dwarf planet Pluto) in our solar system, scientists have hypothesized that there is another planet, provisionally called “Planet Nine.” This hypothetical giant planet would be on the edge of the Solar System. The existence of the planet would explain the unusual orbital configuration of a trans-Neptunian object group (OTN).
About Planet Nine
On January 20th, 2016, researchers Konstantin Batygin and Michael E. Brown of the California Institute of Technology announced that there is additional indirect evidence of the existence of a new planet beyond the orbit of Neptune.
It would orbit around the Sun in between 10,000 and 20,000 years. According to the study published in the Astronomical Journal, “Planet Nine” would have a mass about ten times larger than Earth and would be at least 200 AU far.
Our Solar System
The system is located in one of the outer arms of the Milky Way galaxy (more precisely in the Orion Arm), a galaxy that has approx. 200 billion stars.
Our solar system formed about 4.6 billion years ago as a result of the gravitational collapse of a giant molecular cloud. The most massive space object is the central star – the Sun, while the second object by mass is the planet Jupiter.
The four small inner planets, Mercury, Venus, Earth, and Mars, called terrestrial planets / telluric planets (or rocky planets), are mainly composed of rocks and metal. The four outer planets, called gas giants, are much more massive than the telluric ones.
The two most massive planets, Jupiter and Saturn, are mainly composed of hydrogen and helium; the two furthest planets, Uranus and Neptune, are primarily composed of substances with a relatively high melting temperature (compared to hydrogen and helium), such as ice, water, ammonia, and methane. They are called “ice giants” (a term distinct from that of “gas giant”). All planets have near-circular orbits arranged in an almost flat disk called an ecliptic plane.
Why Planets Have Their Size Limits
In short, that happens because of the way the planets form and behave in their early formation stages. Accordingly, a planet either stays small or grows large. If it remains small, it most likely will become a rocky planet. On the other hand, if it grows large, it accumulates gas in its atmosphere so that it will become a gas giant, such as Jupiter and Saturn in our solar system.
The orbit of a forming planet is also essential for its development. If a planet gets closer to its host star, the molecules in its atmosphere will heat up and disappear. Accordingly, many small rocky planets are just the inner cores of gas giants that got to close to their respective sun.
In conclusion, planets have their size limits because of the circumstances present during their formation. In accordance, a world as big as Planet Nine could exist, hypothetically speaking. Judging on its wide orbit, however, it might be impossible for it to be there for real.