Formation of the Solar System

Origin of the Solar System

• Theories of solar system formation must explain key facts such as each planet's isolation and the nearly circular orbits.
• Planetary orbits lie in a common plane and rotate in the same direction as the Sun's rotation.
• The Nebular Theory proposes that the solar system originated from a collapsing cloud of dust and gas, leading to the Sun's formation at the center.

Nebular Theory

• The interstellar cloud collapses under its own gravity, forming protoplanetary nebulae.
• Angular momentum conservation leads the collapsing cloud to spin faster and flatten into a disk.
• This theory accounts for major solar system characteristics and exceptions.

Condensation Theory

• The gas in the nebula does not clump into planets without interstellar dust acting as condensation nuclei.
• Dust grains, remnants of old stars, allow other atoms to attach and start the planet formation process.

Characteristics of the Solar System

• All planets orbit in the same direction and plane, with closer planets being smaller and rocky, while outer planets are larger and gas-rich.
• Most moons orbit their planets in the same direction as their planets orbit the Sun.
• The oldest meteorites date to about 4.566 billion years old.

Galaxies and the Milky Way

• The Sun is one of trillions of stars in the universe, grouped into galaxies.
• The solar system is part of the Milky Way galaxy.

Spinning Planets: Rotation and Revolution

• The period of rotation is the time taken for a planet to complete one spin (e.g., 1 Earth day).
• The period of revolution is the time taken to orbit the sun once (e.g., 1 Earth year).

Inner Planets (Terrestrial Planets)

• Mercury: Fastest orbit, extreme temperature variations, weighs 38% less than on Earth.
• Venus: High atmospheric pressure, volcanic activity, known as the "evening star," and rotates in the opposite direction to Earth.
• Earth: Perfect temperature range supports liquid water, unique for life, 365-day revolution.
• Mars: Thin atmosphere, evidence of historical water, features the tallest volcano (Olympus Mons), and has two moons.

Outer Planets (Gas Giants)

• Jupiter: Largest planet, features a massive storm (Great Red Spot), short rotation period.
• Saturn: Known for its extensive ring system, largest rings made of icy particles, 18 moons.
• Uranus: Unique axial tilt of 90 degrees, blue-green color, 21 moons named after Shakespearean works.
• Neptune: Discovered in 1846, visible cloud belts, has seven thin rings and eight moons.

Differences in Planet Types

• Giant (Jovian) Planets: Composed mainly of gases, form quickly, and have massive cores.
• Terrestrial (Earth-like) Planets: Composed of solid material, form slower, and have rocky cores.

Gravity and Inertia

• Gravity pulls objects toward each other; inertia is the tendency of objects in motion to remain in motion.
• Both forces work together to maintain the orbits of planets and moons within the solar system.

Other Space Objects

• Comets: Composed of dust, rock, gas, and ice; originate from distant regions.
• Asteroids: Large irregularly shaped rocks primarily in the asteroid belt between Mars and Jupiter; can collide with other bodies and create craters.
• Meteoroids: Small rock or dust particles; when entering Earth's atmosphere, they produce meteors, and if they land, they become meteorites.