solars system 1

Planet Earth is considered habitable because of the following reasons:

  • it has the right distance from the sun

  • it is protected from harmful solar radiation by its magnetic field

  • it is kept warm by an insulating atmosphere

  • it has the right amount of ingredients for life, including water and carbon.

Earth, Venus, and Mars have differences

  • Venus has no water

  • Venus and Mars don’t have oxygen;

  • Earth has life forms.

Earth, Venus, and Mars may have similarities

  • They all are terrestrial planets, made of solid rocks and silicates

  • They all have an atmosphere

  • They all almost have the same time to rotate on their axes

  • Earth and Mars both have water

  • They all have carbon dioxide

  • All have landforms.

Big Bang Theory

  • Proposed by Georges Lemaître

  • It suggests that the universe began as a singular, extremely dense point that expanded rapidly about 13.8 billion years ago.

  • It led to the formation of galaxies, stars. and planets

Expanding Universe Theory

  • By Edwin Hubble

  • It suggests that the universe has been expanding since its explosive beginning around 13.8 billion years ago

  • The expansion means that galaxies are moving away from each other, which is supported by redshift in light in distant galaxies

Steady State Theory

  • It suggests that the universe has always existed in a constant state, with new matter being created as the universe expands

Rare Earth Hypothesis

  • It argues that complex life is rare in the universe because it requires a specific combination of conditions such as: earth’s stable orbit, plate tectonics, and a large moon to stabilize its tilt, leading to a relatively mild climate.

Multiverse Theory

  • It suggests that the universe is just one of many, each with different physical laws and constants

Gaia Hypothesis

  • It proposes that earth’s living organisms interact with their inorganic surroundings to maintain conditions favorable for life, treating the plant as a self-regulating system

Panspermia Theory

  • It suggests that the earth may have originated from microorganisms or chemical precursors of life, which were brought here by comets, asteroids, or space dust

Theories about Solor System

Nebular Hypothesis

  • Proposed by Immanuel Kant

  • It suggests that the solar system formed around 4.6 billion years ago from a giant cloud of gas and dust known as solar nebula

  • Under the influence of gravity, the nebula began to collapse, forming a spinning disk. The materials were pulled toward the center, creating the sun, while the rest of the disk turned into other celestial bodies

  • This explains why the planets orbit the sun in the same direction and lies roughly in the same plane

Planetesimal Hypothesis

  • Proposed by Thomas Chrowder Chamberlin and Forest Ray Moulton

  • It expands the nebular hypothesis, suggesting that planets formed form from small, solid objects called planetesimals.

  • These planetesimals collided and stuck together gradually growing into larger bodies.

Protoplanet Hypothesis

  • Proposed by William Hunter McCrea

  • A variation of nebular hypothesis, the protoplanet hypothesis proposes that the solar system began as a cloud of gas and dust that collapsed into a rotating disk. Within this disk, eddies of gas and dust formed and grew into protoplanets which eventually became into planets

  • This explains the difference between the inner rocky planets and outer gas giants

Capture theory

  • Proposed by Michael Mark Woolfson

  • It suggests that the sun captured rouge planets or planetesimals that were floating in space

  • This could explain the irregular orbits of some moons and small bodies in the solar system but this could not explain the orderly structure of the planet’s orbits.

Modern Laplacian theory

  • Proposed by Pierre-Simon Laplace

  • It suggests that the solar system formed a contracting and cooling rotating cloud of gas and dust. As the cloud contracted it spun faster leading to the formation of the central mass/sun and a surrounding disk that eventually became planets

  • Emphasizes the angular momentum in the formation process

Solar Fission theory

  • Proposed by George Darwin

  • It suggests that the planets were once part of the sun and were flung off due to the Sun’s rapid motion

  • This theory has largely been discredited because it does not account for the differences in composition between the sun and planet