New Earth-Like Planet Hiding in Outer Solar System, Astronomers Suggest

An artist's rendering shows a moon with a diameter roughly 2.6 times that of Earth orbiting a large gas giant planet in another solar system located about 5,700 light years from our solar system, in an undated handout illustration. Helena Valenzuela Widerstrom/Handout via Reuters

Two astronomers in Japan have recently uncovered possible evidence that points to the existence of an Earth-like planet, referred to as “Planet Nine,” in the outer solar system beyond Neptune.

The two astronomers—Patryk Sofia Lykawka of Japan’s Kindai University and Takashi Ito of Japan’s National Astronomical Observatory—published their research study in the Astronomical Journal on Aug. 25.

The study unveils the possible presence of a massive Earth-like planet in the Kuiper Belt—“a doughnut-shaped ring of icy objects” that encircles the sun, stretching beyond the orbit of Neptune, according to NASA.

“We predict the existence of an Earth-like planet and several TNOs [trans-Neptunian objects] on peculiar orbits in the outer solar system, which can serve as observationally testable signatures of the putative planet’s perturbations,” the scientists said.

The scientists projected that Planet Nine would have a mass of 1.5 to 3 times that of Earth, located 500 astronomical units (AU) from the sun, with an orbit inclination of 30 degrees, if it indeed exists.

They believe that the discovery of such a planet can help unravel fundamental properties of the Kuiper Belt, including “a prominent population of trans-Neptunian objects with orbits beyond Neptune’s gravitational influence, a significant population of high-inclination objects, and the existence of some extreme objects with peculiar orbits.”

“It is plausible that a primordial planetary body could survive in the distant Kuiper Belt as a KBP [Kuiper Belt planet], as many such bodies existed in the early solar system,” the researchers wrote in the study.

“More detailed knowledge of the orbital structure in the distant Kuiper Belt can reveal or rule out the existence of any hypothetical planet in the outer solar system.

“The existence of a Kuiper belt planet may also offer new constraints on planet formation and dynamical evolution in the trans-Jovian region.”

According to NASA, astronomers have been studying the potential existence of a ninth planet that could explain the peculiar orbits of several Kuiper Belt objects.

‘Bizarre, Highly Elongated Orbit’

In 2016, California Institute of Technology researchers found evidence of a planet “tracing a bizarre, highly elongated orbit” in the outer solar system, which has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than Neptune does.

The researchers, Konstantin Batygin and Mike Brown, estimated that this new planet would take 10,000 to 20,000 years to make just one full orbit around the sun.

The planet hasn’t been observed directly. The researchers discovered the planet’s existence through mathematical modeling and computer simulations.

Mr. Brown said the putative ninth planet, which is 5,000 times bigger than Pluto, is sufficiently large enough that there should be no debate about whether it’s a true planet.

“This would be a real ninth planet,” he said.

“There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.”