Planetary system

Artist Concept Planetary System

De Revolutionibus manuscript p9b

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Protoplanetary discs observed with SPHERE

Morgan-Keenan spectral classification

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Planetary system refers to a collection of non-stellar objects that orbit a star or stellar remnant. At the core of a planetary system is typically a single star, around which planets, dwarf planets, asteroids, comets, and meteoroids revolve due to gravitational forces. The most well-known planetary system is the Solar System, which includes Earth and other planets orbiting the Sun.

Components of a Planetary System

A planetary system can include various types of bodies, including, but not limited to:

• Planets: Large bodies that orbit a star and have cleared their orbits of other debris. Planets can be either terrestrial planets, with solid rocky surfaces, or gas giants and ice giants, which are primarily composed of gases or ices.
• Dwarf Planets: Bodies that are similar to planets but have not cleared their orbits of other debris.
• Moons: Natural satellites that orbit planets or dwarf planets.
• Asteroids: Small rocky bodies that orbit the star, mainly found in the asteroid belt between Mars and Jupiter in our Solar System.
• Comets: Icy bodies that release gas or dust when close to the star they orbit, often creating visible atmospheres or tails.
• Meteoroids: Smaller rocks or particles in orbit around a star.

Formation and Evolution

Planetary systems are believed to form from the gravitational collapse of a molecular cloud into a protostellar disk, also known as a protoplanetary disk. Over time, particles within the disk collide and stick together, forming larger bodies through a process called accretion. Eventually, these bodies become large enough to form planets and other components of the planetary system.

The evolution of planetary systems is influenced by various factors, including the mass and type of the central star, the distribution of mass in the protoplanetary disk, and interactions between the forming bodies. Over time, planetary systems can undergo significant changes, such as planetary migrations, collisions, and the ejection of bodies from the system.

Detection and Study

The study of planetary systems beyond our own became feasible with the development of various astronomical observation techniques. The most common methods for detecting exoplanets (planets outside the Solar System) include the transit method, which observes the dimming of a star as a planet passes in front of it, and the radial velocity method, which detects changes in a star's velocity due to the gravitational pull of an orbiting planet.

Notable Planetary Systems

Aside from the Solar System, there are many other planetary systems that have been discovered, each with unique characteristics. Some notable examples include:

• The TRAPPIST-1 system, known for having seven Earth-sized planets, three of which are in the habitable zone where liquid water could exist.
• The Kepler-90 system, which has a total of eight known planets, matching the number of planets in our own Solar System.

Challenges and Future Research

The study of planetary systems faces several challenges, including the vast distances to these systems, which make direct observation difficult. Future research aims to improve detection methods, understand the formation and evolution of planetary systems, and potentially identify habitable planets that could support life.