The chances of a massive object larger than Jupiter orbiting our Sun in the outer regions of the solar system and remaining undiscovered are difficult to estimate definitively. However, it is important to note that the existence of such a hypothetical object, often referred to as "Planet Nine" or "Planet X," is a topic of ongoing scientific investigation and debate.
The idea of a hidden, massive planet beyond the orbit of Neptune has been proposed to explain certain peculiarities observed in the outer solar system. These include the clustering of the orbits of some distant Kuiper Belt objects and other indirect evidence suggesting the presence of a large, undiscovered celestial body.
While the existence of Planet Nine remains unconfirmed, astronomers continue to search for evidence through various methods, including direct observation and analysis of the gravitational effects on other objects. However, the vastness of the outer solar system and the inherent challenges of detecting and characterizing distant objects make the search a complex task.
As for the chances of an undiscovered massive object existing in the outer solar system, it is difficult to provide a precise estimation. The search for such objects is ongoing, and new discoveries are being made regularly. It is worth noting that in recent years, several large and distant objects, such as Eris and Sedna, have been discovered beyond Neptune, expanding our knowledge of the outer solar system.
While it is scientifically plausible for a massive object to remain undetected in the outer regions of our solar system, the exact probability is uncertain. Future advancements in observational techniques, technologies, and theoretical models may shed more light on this intriguing question and refine our understanding of the outer solar system.