Mysterious Earth-sized planet could be hiding in plain sight in our Solar System

Astronomers have found likely evidence of an Earth-like planet in the Solar System that may be circling the Sun in an orbit beyond Neptune.

Physicists, including those from the National Astronomical Observatory of Japan, said the planet could be much closer than the hypothetical Planet Nine thought to exist in the far outer edges of the Solar System.

Several studies in the past have suggested there is likely a yet-undiscovered planet beyond the Kuiper Belt – a stellar disk of materials such as asteroids, space rocks, comets around the Sun in the outer Solar System past the orbit of Neptune.

In the new research, published recently in The Astronomical Journal, scientists found that some of the objects in the Kuiper Belt behave in a way indicative of the presence of a small planet among them.

One such object, they said, is about 500 astronomical units (AU) from the Sun, where 1 AU is the distance between the Sun and the Earth.

In comparison Neptune is at a distance of 30 AUs from the Sun.

Some of these were also found to have “odd” orbits suggesting they are being pull by the gravity of a cosmic entity larger than those that typically influence such objects.

Computer simulations run by the scientists indicate that the most likely explanation for the observations was another hidden planet in the Kuiper Belt.

“We predict the existence of an Earth-like planet,” researchers wrote in the study.

“It is plausible that a primordial planetary body could survive in the distant Kuiper Belt as a Kuiper Belt planet (KBP), as many such bodies existed in the early solar system,” they added.

If such a planet exists, researchers say it would have a mass about 1.5 to 3 times that of Earth with an inclination of about 30 degrees.

They say the theorised planet’s orbit would likely place it between 250 and 500 AU from the Sun.

Researchers say the discovery of such a planet close to the Kuiper Belt can unravel new constraints on planet formation and evolution.

“In conclusion, the results of the KBP scenario support the existence of a yet-undiscovered planet in the far outer solar system,” scientists noted.