Detailed Notes on the Solar System and its Formation

Definition: The solar system consists of the sun and everything in orbit around it.
- Nearly all mass (~99.8%) is in the Sun.
- Remaining mass is in planets, moons, and smaller celestial bodies.
- Plutoids: Icy and rocky objects located in the Kuiper Belt.
- Asteroids: Rocky bodies, primarily found between Mars and Jupiter.
- Comets: Composed of ice and rock, often visible with tails when close to the sun.
- Meteoroids: Small fragments from comets and asteroids.

Orbital Direction: Planets orbit the sun from west to east, counterclockwise when viewed from Earth's North Pole.
Orbit Shape: While Kepler describes orbits as elliptical, they are nearly circular for all planets except Pluto.
Planet Classification:
- Terrestrial Planets: Inner planets (Mercury, Venus, Earth, Mars)
- Composition: Rock and iron.
- Characteristics: High density, smaller size (~10,000 km in diameter).
- Jovian Planets: Outer planets (Jupiter, Saturn, Uranus, Neptune)
- Composition: Gases like hydrogen, helium, methane, and ammonia.
- Characteristics: Lower density, significantly larger size (~100,000 km in diameter).

Density Definition: Density = mass / volume.
Common Materials Densities:
- Water: ~1000 kg/m³
- Metal: ~5000 kg/m³
Celestial Bodies:
- Density for bodies like the Sun, Jupiter, Saturn: ~1000 kg/m³.
- Density for terrestrial bodies: closer to 5000 kg/m³.

Evolution of Large Bodies: Understanding the historical context of the solar system entails focusing on small celestial bodies.
Key Clues from Small Bodies:
- Asteroids and Comets: Hold records of the solar system's evolution.
- Meteorites: Fragments that hit Earth; primarily come from asteroids.

Characteristics:
- Rocky bodies bound by gravity, mostly found in the asteroid belt between Mars and Jupiter.
- Ceres: Largest asteroid with a diameter of ~1000 km.
- Near-Earth asteroids (NEAs) have orbits crossing Earth's path.
- Trojan Asteroids: Orbit alongside a planet in stable regions.
Composition:
- Varied: Some have iron cores and rock or icy exteriors.
- Carbonaceous Asteroids: Dark, contain water ices and organic materials.
- Silicate Asteroids: Reflective, mostly rocky.

Definition: Composed of icy and rocky materials; often referred to as "dirty snowballs".
Size: Typically 1 to 10 km.
Coma and Tail:
- Coma: Halo of gas and dust created when ices sublimate near the sun.
- Tails: Composed of gas and dust, always point away from the sun due to solar wind.
Orbits: Usually thousands of years long, originating from the Oort cloud or Kuiper belt.

Definition: Small rocky or metallic bodies in the solar system.
Transformations:
- Meteors: Burning meteoroids in Earth's atmosphere.
- Meteorites: Meteors that reach the ground.
Commonality: 95% of meteorites are rocky; the rest include iron and rare carbonaceous chondrites.

Impact Frequency: Varies from monthly to every million years for significant impacts.
Evidence of Extinction Events:
- Iridium-rich clay layer correlating with a major asteroid strike 65 million years ago, thought to have contributed to dinosaur extinction.
- Chicxulub crater: Evidence of the impact's location.

Nebular Hypothesis: Proposes the solar system formed from a collapsing gas cloud into a disk.
Key Features:
- Most mass is in the Sun.
- Planets formed in a rotating disk, resulting in nearly circular and coplanar orbits.
Protoplanet Formation:
- Dust and gas condense, clumping into planetesimals, then evolving into protoplanets.
Accretion: Cores gather more material; heavier elements differentiate to form structural layers in terrestrial planets.

Moon formation likely resulted from a giant impact with a Mars-sized body during Earth's early stages, ejecting material into orbit.

Formation involves gathering gas onto rocky cores, with significant growth occurring past the snow line where ice could form.

Early solar system dynamics involved significant ejection and scattering of planetesimals, primarily influenced by Jupiter's gravity.

The solar system's structure and formation can be understood through the interplay of gravitational forces, gas dynamics, and the history of impacts.