multiplanet

Multiplanet is an adjective or noun describing something involving more than one planet. In astronomy it refers to a star system with two or more planets orbiting a common star. In futurism and space policy it is used to discuss humanity extending settlement across multiple planets.

In astronomy, a multiplanet system is a star that hosts two or more confirmed planets. Such systems are common among exoplanets, and many are compact with several planets in close orbits. Examples include the TRAPPIST-1 system, which has seven planets, and Kepler-90, a large family of planets in a single system. Studying these systems informs models of planetary formation and orbital dynamics.

In discussions of space exploration, the term describes the goal of establishing durable human presence beyond Earth on more than one world, notably Mars. It has been popularized by policy and industry leaders who describe humanity as a multiplanetary species. Achieving this objective requires advances in propulsion, life support, habitat design, radiation protection, in-situ resource utilization, and robust planetary protection practices.

Terminology notes: multiplanet is less common than multiplanetary or multi-planet; authors may use hyphenated forms such as multi-planet. The concept spans scientific understanding of real multiplanetary systems and speculative plans for future settlement.