Formation of the Solar System

Scientific Theories on Formation of the Solar System

Nebular Hypothesis (Modern Nebular Theory)

• Massive molecular cloud collapsed under gravity to form the solar system around 4.6 billion years ago
• Sun originated at the center of the collapsing mass, with the remaining mass flattening into a protoplanetary disc
• Planets, moons, and other objects formed from this disc through accretion
• Angular momentum played a crucial role in forming the disc
• Disc temperature variations impacted planet makeup
• The "frost line" divides the development of rocky and gaseous planets

Theories on Formation of the Planets

• Modern Nebular Theory: solar nebula collapsed to form the Sun and planets
• Rocky materials formed terrestrial planets (Mercury, Venus, Earth, and Mars) near the Sun
• Gas giants (Jupiter and Saturn) formed further away from the Sun
• Alternative theories: encounter hypothesis, protoplanet hypothesis, and migration idea

Theory on Formation of the Moons (Giant Impact Hypothesis)

• Oblique collision between proto-Earth and Theia (a planetary body the size of Mars) around 4.5 billion years ago
• Impact launched debris into orbit, which gradually formed the Moon over weeks to years
• Moon's composition is iron-depleted, similar to Earth's mantle
• Supporting evidence: identical oxygen isotope ratios in rocks from Earth and Moon

Theory on Formation of Asteroids (Asteroid Belt Formation Theory)

• Asteroid belt was initially empty and formed from excess rocky material during the formation of terrestrial planets
• Material was gravitationally flung outward, implanting S-type (stony) asteroids into the inner main belt
• Gas giants' formation destabilized neighboring planetesimals, injecting C-type (carbon-rich) asteroids into the outer main belt

Theories on the Formation of Comets

• Comets likely formed in outer areas beyond the "frost line" around 4.6 billion years ago
• Comets come from the Kuiper Belt and Oort Cloud
• Comet composition: solid bodies made of ice, dust, and small rock fragments
• Comets are a mixture of water ice and other volatile substances that evaporate when approaching the Sun