Planet nine may exist on the far reaches of the solar system, frigid and dark, as it orbits well beyond the rounded path of Neptune. Although the world has not yet been observed, astronomers are starting to theorize what conditions may be like on the mysterious planet.

Gravitational forces from the distant planet could explain some observations made of objects in the depths of the solar system.

Researchers speculate the world would have a diameter roughly 3.7 times that of our own home world, and a mass equal to 10 times here on Earth. The planet should, theoretically, orbit in an egg-shaped orbit, between 200 and 1,200 times further away from the sun than does our home world. Planet nine would likely be a smaller version of a gas giant, looking much like Uranus or Neptune. This model would suggest an icy core, surrounded by a thick atmosphere containing the two most abundant elements in the Universe, hydrogen and helium.

If planet nine exists, temperatures on the world could dive down to 375 degrees below zero Fahrenheit. This is significantly warmer than would be expected if the main energy released by the planet were reflected from the distant sun.

"This means that the planet's emission is dominated by the cooling of its core, otherwise the temperature would only be 10 Kelvin. Its intrinsic power is about 1000 times bigger than its absorbed power," said Esther Linder of the University of Bern.

Calculations seem to suggest the mystery world may be at its apogee, or greatest distance from the sun, making it particularly hard to find at this time. However, there have been a few tantalizing clues from various observatories which seem to show some bizarre objects beyond Neptune. The Wide-Field Infrared Survey Explorer may have found a body possessing 50 times the mass of Earth at the outskirts of the solar system.

In January 2016, a pair of astronomers from Caltech, Mike Brown and Konstantin Batygin, reported their discovery that some Kuiper Belt objects (KBO's) were following strange orbits that could be explained by the presence of an unseen world beyond Neptune.

In 1846, the eighth planet, Neptune, was discovered after astronomers found gravitational evidence of its existence. Today, astronomers are even studying the movement of the New Horizons spacecraft, traveling beyond the orbit of Pluto, to see if the distant world might exist.

Analysis of the potential physical properties of a planet nine are due to be published in the journal Astronomy & Astrophysics.

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