What is a defining feature of a planet in our solar system?

A defining feature of a planet in our solar system is that it must orbit a star. This criterion is fundamental to the definition of a planet, as it distinguishes planets from other celestial objects. In our solar system, the star is the Sun, and all planets, including Earth, Mars, and Jupiter, revolve around it due to gravitational forces. This orbital relationship is essential for the classification of an object as a planet.

Other choices do not accurately define what constitutes a planet. For instance, visibility to the naked eye can vary depending on several factors, including light pollution and the observer's location, making it an unreliable criterion. The presence of moons is also not a requirement, as there are planets without any moons, like Mercury and Venus. Additionally, while planets have diverse compositions—ranging from gaseous giants to rocky terrestrial bodies—having a specific composition of rock and gas is not a strict requirement for defining a planet; it’s their orbital pattern around a star that is the primary characteristic.