Composition and Formation of the Universe and Solar System

Formation of the Universe

• Cosmology Hypothesis: Scientific study of the universe's beginning based on current physical and chemical properties.

• Big Bang Theory: The prevailing model for early development. It is supported by Cosmic Microwave Background (CMB), considered the oldest light (released $380\,000\text{ years}$ after the big bang).

• CMB Characteristics:

  • Detected as a "glow" or remnant radiation.
  • Suggests the early universe was denser and hotter ($5.5 \times 10^9\,^{\circ}\text{C}$) with hydrogen plasma, neutrons, electrons, and protons.
  • Current measured age of the universe is $13.82 \times 10^9\text{ years}$.

• Cosmic Inflation Theory: Proposed by Alan Guth and Andrei Linde (1980s).

  • Suggests the early universe was a bubble of pure vacuum energy that underwent rapid expansion.
  • Explains the homogeneity (uniformity) and flatness (lack of curvature) of the universe.
  • Density fluctuations during expansion led to the formation of stars and galaxies.

• Steady State Theory: Proposed by Sir James Jeans (1920) and revised by Sir Fred Hoyle, Sir Hermann Bondi, and Thomas Gold (1948).

  • Claims the universe has no beginning or end and maintains a constant appearance despite expansion.
  • Now considered obsolete due to the discovery of distant ancient bodies like quasars and radio galaxies, proving the universe is dynamic.

Origin of Star Systems

• Nebular Hypothesis: Developed by Immanuel Kant and Pierre-Simon Laplace.

  • Suggests the solar system formed $\sim 4.5 \times 10^9\text{ years}$ ago from a rotating cloud of hot gas (nebula) that shrunk and cast off rings of gas to form planets.

• Planetesimal Theory: Proposed by Viktor S. Safronov (1941) and developed by T. C. Chamberlin and F.R. Moulton.

  • Planets formed via the accretion of small space bodies until their gravity increased their size.

• Tidal Theory: Developed by James Jeans and Sir Harold Jeffreys (1917).

  • A passing star pulled matter from the sun through tidal forces, which cooled into solid planetesimals.

Planetary Categories

• Inner Planets (Terrestrial/Telluric): Mercury, Venus, Earth, and Mars.

  • Located between the sun and the asteroid belt.
  • Characterized by compact, rocky surfaces ($\text{silicate rocks}$) and metallic cores.

• Outer Planets (Jovian/Gas Giants): Jupiter, Saturn, Uranus, and Neptune.

  • Located beyond the "frost line."
  • Composed primarily of $H_2$ and $He$.
  • Massive and less dense due to gas condensation in lower temperatures.

The Terrestrial Planets

• Mercury: Smallest and closest to the Sun ($57\,910\,000\,km$).

  • Lacks a substantial atmosphere.
  • Massive iron core; features a "cometary tail" $2.5 \times 10^6\,km$ long.
  • Atmosphere composition Includes: OXYGEN $420\%$, 500IUM $29.0\%$, and HYDROGEN $22.0\%$.

• Venus: "Earth's twin" in size and mass.

  • Atmosphere is dense $CO_2$ causing a runaway greenhouse effect; surface temp averages $462\,^{\circ}\text{C}$.
  • Exhibits retrograde motion (Sun rises in the west).

• Earth: Unique for abundant liquid water ($70\%$ coverage) and life.

  • Atmosphere rich in $N_2$ and $O_2$.
  • Only terrestrial planet with a substantial global magnetic field due to a liquid metal outer core.
  • Features active plate tectonics.

• Mars: The "Red Planet" due to $iron\,oxide$ (rust).

  • Atmosphere is $95.3\%$ $CO_2$ with low pressure ($0.6\%$ of Earth's).
  • Two moons: Phobos and Deimos (captured asteroids).
  • Major features: Olympus Mons (largest volcano) and Valles Marineris (canyon system).