To determine whether something could have been a planet, we should consider its characteristics and how they align with the criteria that define a planet. According to the International Astronomical Union (IAU), a celestial body must meet the following criteria to be considered a planet:
It must orbit the Sun or another star.
It must be spherical in shape, achieved by reaching hydrostatic equilibrium, which occurs when the body’s gravity pulls it into a nearly round form.
It must have cleared its orbital path of other debris, meaning it is gravitationally dominant in its vicinity.
If the object in question was part of a solar system and displayed these characteristics at some point in its history, then it might have been classified as a planet. For instance, it could have been a protoplanet during the early formation stages of a solar system, potentially losing its status due to events like collisional disruption, gravitational perturbations, or significant mass loss that caused it to lose its spherical shape.
In evaluating whether it could have been a planet, one would also take into account the object’s current and past size, composition, and orbital dynamics. Observations or models would help in understanding its history and the processes it underwent. If evidence suggests adherence to these criteria at some time, then it is plausible that it was once a planet.