Simulations suggest an Earth or Mars size planet may be lurking out beyond Neptune

Phys.org ^ | October 4, 2021 | Bob Yirka ,

[BenLurkin]

As scientists continue to study the solar system, they are still trying to understand not only how the planets came to exist but why they occupy their current orbits. In this new effort, the authors note that simulations of the evolution of the solar system are not yet able to explain the current configuration due to missing information. And they suspect that the missing information involves a planet that once circled the sun in the outer solar system (where the gas giants, Jupiter, Saturn, Uranus and Neptune reside) but now exists out beyond the edges of the solar system or even in deep space.

The authors note that there is something odd about the current configuration of the planets, which has four inner rocky planets, an asteroid belt and then four gas giants in the outer solar system. Past the giants are dwarf planets and other objects such as comets.

The researchers...contend that it is unlikely that the natural evolution of our solar system would have four gas giants and then nothing but dwarfs.

Adding another Earth- or Mars-sized planet to the outer solar system, perhaps between two of the gas giants, produces a more accurate model—at least during the early stages of development. Eventually, such a planet would have been pushed farther out into space, either joining the dwarfs, or was driven all the way out into interstellar space, where it would travel alone.

...[N]ew telescopes under construction may be able to spot it and thus confirm their theory.

[SunkenCiv]

Dr. Sako is currently hunting for the putative giant planet -- Planet Nine -- that might be lurking in the outskirts of our Solar System. Planet Nine, if real, could be as large as ten Earth masses, but will only appear as a faint little dot due to its vast distance from the Sun. Dr. Sako and students use supercomputers to sift through the many millions of detections and background stars, galaxy, and other minor bodies in the solar neighborhood. Its discovery and nature will teach us about the history and formation of our Solar System. Masao Sako is an astrophysicist using large telescopes, supercomputers, and big data to study the Universe. He is the recipient of numerous teaching awards at the University of Pennsylvania, including the Lindback Award for Distinguished Teaching and the Dean’s Award for Innovation in Teaching. This talk was given at a TEDx event using the TED conference format but independently organized by a local community.

The Search for Planet Nine | Masao Sako | TEDxPenn | May 31, 2018 | TEDx Talks

[glennaro]

There sure is (admittedly a bit smaller) ... it's called "Pluto".
(I can't help it, I'm a Pluto-is-the-ninth-planet fan, escaped moon or not!)