Sunplanet

Sunplanet is a hypothetical celestial body used in speculative astronomy and science fiction to denote a planet that orbits the Sun. Unlike confirmed planets, it is not anchored to observable data and appears primarily in thought experiments and narrative contexts. The term is occasionally used as a placeholder name in discussions about solar system architecture.

In most treatments, Sunplanet is imagined as distant from the Sun, at tens to hundreds of astronomical units, with an orbital period spanning centuries or millennia. Its orbit may be highly eccentric or inclined, which helps illustrate the effects of gravitational interactions with outer solar-system bodies on long-term stability.

The physical characteristics of Sunplanet vary. Some depictions describe a rocky super-Earth or ice giant with a substantial atmosphere, while others portray a gas giant with complex weather systems and possibly strong magnetospheres. The ambiguous nature of the concept makes standardized composition unlikely.

The concept is used in discussions of planetary formation and migration, to explore how distant planets could form or be perturbed into distant orbits. It also serves as a narrative device in speculative fiction, enabling explorations of isolation, climate extremes, and long-term solar evolution.

In scholarly contexts, Sunplanet is treated as a hypothetical case study rather than a detected object. Researchers emphasize the importance of robust detection methods for identifying distant solar-system bodies and the challenges in distinguishing such objects from observational biases.