There's a 7% percent chance an ice giant planet is hiding in our solar system

Could it be you, Planet X?
Sade Agard
A frozen 'unknown' exoplanet lit by a nearby star
A frozen 'unknown' exoplanet lit by a nearby star


Scientists have just calculated that there's a seven percent chance of another neighboring planet within our solar system, according to a new study published to the preprint server arXiv (yet to be peer-reviewed). Although the odds may appear slim, let's focus on the fact that they're not zero either.

This enigmatic world, the researchers speculate, would likely reside in the distant Oort cloud— a spherical region teeming with icy fragments and comets, spanning billions to trillions of miles from the sun.

Where could the ice giant planet be hiding?

Pluto's controversial reclassification as a dwarf planet, reducing our solar system's planet count from nine to eight, hasn't deterred astronomers from their quest for discovery. 

Drawing inspiration from Percival Lowell's relentless pursuit in 1906, a segment of the scientific community remains committed to the existence of a colossal planet, nicknamed "Planet X," lurking beyond Neptune's domain.

Now, in this latest study, an international team simulated the unstable celestial mechanics of the early solar system, proposing there could be an icy giant situated much farther away than Lowell could have predicted.

"It's completely plausible for our solar system to have captured such an Oort cloud planet," co-author Nathan Kaib, told Popular Science.

"These hidden strangers are "a class of planets that should definitely exist but have received relatively little attention," emphasized Kaib, who is an astronomer at the Planetary Science Institute.  

According to the study, giant planets like Jupiter, Saturn, Uranus, and Neptune form twin siblings. However, their powerful gravity leads to turbulent interactions, destabilizing the young solar system. 

Occasionally, a planet gets ejected from the system or pushed to the outer regions, resulting in peculiar orbital characteristics that trace its journey.

"The survivor planets have eccentric orbits, which are like the scars from their violent pasts," said lead author Sean Raymond, a researcher at the University of Bordeaux's Astrophysics Laboratory. 

Raymond explained that an exiled Oort cloud planet would be distant from its star and have an elongated orbit resembling a comet's ellipse, unlike Earth's nearly circular path. Due to the vast distance, detecting such a planet is highly challenging, as it would be faint.

Could the ice giant be Planet X?

Intriguingly, Raymond and his team explained that the Oort cloud planet could not be the 'Planet X' pursued by Lowell.

"The Oort cloud planets in our simulations would be much more distant than the proposed Planet Nine orbit—at least 10 times further away," highlighted Kaib. "Our simulations cannot place planets on Planet-Nine-like orbits."

Did you notice Kaib's use of the term' planets,' implying the presence of multiple hidden celestial bodies? At the least, these findings emphasize the vast untapped potential for discovery within our own solar system.

The complete study was published in Arxiv and can be found here.

Study abstract: 

Dynamical instabilities among giant planets are thought to be nearly ubiquitous, and culminate in the ejection of one or more planets into interstellar space. Here we perform N-body simulations of dynamical instabilities while accounting for torques from the galactic tidal field. We find that a fraction of planets that would otherwise have been ejected are instead trapped on very wide orbits analogous to those of Oort cloud comets. The fraction of ejected planets that are trapped ranges from 1-10%, depending on the initial planetary mass distribution. The local galactic density has a modest effect on the trapping efficiency and the orbital radii of trapped planets. The majority of Oort cloud planets survive for Gyr timescales. Taking into account the demographics of exoplanets, we estimate that one in every 200-3000 stars could host an Oort cloud planet. This value is likely an overestimate, as we do not account for instabilities that take place at early enough times to be affected by their host stars' birth cluster, or planet stripping from passing stars. If the Solar System's dynamical instability happened after birth cluster dissolution, there is a ∼7% chance that an ice giant was captured in the Sun's Oort cloud.

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