Celestial Definitions and Solar System Origins

Fundamental Astronomical Definitions

• Dwarf Planet: A celestial body orbiting the Sun that has sufficient mass to assume a nearly spherical shape, but has not cleared its orbital path.
• Sun: The star of our planetary system. It has an average size among stars and derives its energy from thermonuclear reactions occurring in its core.
• Planets: Celestial bodies orbiting the Sun. They can be inner (closer to the Sun) or outer (further from the Sun).
• Satellites: Celestial bodies that revolve around planets.
• Asteroids: Smaller rocky bodies. Most are located in the asteroid belt; others include Trojans and Centaurs.
• Comets: Small celestial bodies composed of ice and dust particles.
• Star: A celestial body that shines in the sky with its own light.
• Nebula: Interstellar masses of dust and gas. Their visibility from Earth can vary based on their density and the presence of star formation within them.
• Galaxy: Each of the vast clusters of stars, nebulae, dust, and gas that are scattered throughout the universe.
• Universe: The totality of all existing matter, including stars, galaxies, planets, nebulae, and dust, created within the overall cosmos.

Criteria for a Scientific Theory

For a theory to be considered scientific, it must meet three essential conditions:

• Based on Fact: It must be founded upon verifiable facts and empirical evidence.
• Explanatory Power: It must effectively explain observed facts and phenomena, making logical sense.
• Falsifiability: It must be possible to test the theory and potentially prove it incorrect through experimentation or observation.

The Planetesimal Theory of Solar System Formation

The Planetesimal Theory describes the formation of our solar system through a series of stages:

1. Initial Nebula: Approximately 4.6 billion years ago, a rotating nebula of gas and dust, larger than our current Solar System, began to contract.
2. Gravitational Collapse: This contraction led to the formation of a central mass and a rotating disk surrounding it.
3. Formation of the Protosun: Collisions of particles within the central mass released significant heat. Nuclear fusion of hydrogen then began, marking the birth of the star (the Sun) within the nebula.
4. Formation of Planetesimals: Dust and gas particles in the rotating disk around the protosun underwent a process of aggregation. This formed granules, then through collisions and mergers, larger bodies called planetesimals, ranging in size from hundreds of meters to kilometers.
5. Formation of Protoplanets: Further collisions and mergers of planetesimals led to the formation of primitive planets, or protoplanets.
6. Orbital Clearing: Through the process of accretion, each protoplanet gradually cleared its orbital zone of remaining planetesimals.