Lecture Five Flashcards
What forces of attraction act upon particles in a nebula?
Particles in a nebula are attracted to one another by gravity, when something is bigger than another thing in space, the gravity of the larger object attracts smaller objects.
They are also either attracted to, or repelled from one another by electrostatic forces.
What points must be explained by a theory of the solar system?
- All planets orbit approximately in the same plane (ecliptic plane).
- Planets all orbit the sun in the same direction as the suns rotation.
- Planetary orbits are nearly circular.
- Planets contain most of the angular momentum of the solar system.
- The sun contains most of the mass of the solar system (~99.8%).
- Distance of a planet from the sun follows a simple rule (Titus-Bode’s Law), except for Neptune.
- Planets differ in composition as you move out from the sun in a constant manner - moons of gas giants do the same. Dense planets closer to the sun and as you move away from the sun, planets become less dense.
- Difference in density between inner (rocky) planets and outer (gas giant) planets.
What is Descartes theory of the solar system?
Solar system formed in a vortex in space - the universe is full of them, our universe is one.
Explained condensation of vortex particles in to planets, and heavier matter in inner solar system, and lighter matter in outer solar system.
Problem!
Universe is not full of vortices.
But…
He was on the right track regarding condensation of planets and predicted that other stars would have planets i.e. star = planets surrounding it.
What is Leplace’s Nebular Hypothesis?
Gaseous clouds - nebula - rotate and collapse under gravity to form stars and planets.
As cloud contracts it spins more rapidly, flattens and throws off a series of gas rings.
Planets (and moons and asteroids etc.) form from material in these rings - asteroids are just bodies that didn’t quite make it to being a planet :(.
Centre of cloud forms sun.
Problem!
Planets in our solar system have 99% of its angular momentum, this cannot be explained by this theory, which suggests that the sun is the lease massive thing in the solar system.
What is the protoplanet theory?
Sun and planets form at the same time within same interstellar cloud, the sun then captures planets, which orbit around it.
Moons and asteroids form from droplets that spin off larger rotating planets when they are still molten.
Problem!
Does not explain why everything orbits int he same direction on the same plane.
Predicts that rock planets should not have moons - we know this is not the case.
Needs new, undiscovered, physical phenomenon “magnetic breaking” to slow down the spin of the sun.
What is the Encounter hypothesis formed by Woolfson?
Sun and wandering protostar get close to each other.
Sun and protostar draw filaments of material out of each other.
That material formes planets - Suns material forms inner planets, protostar material forms outer planets, hence why inner planets are rocky and outer planets are gaseous.
Problem!
This assumes that the sun is older than the planets, which is not the case.
Assumes that the outer planets are composed of different material to the inner planets, not the case, they’re made of the same/similar materials, just in different percentage compositions.
What is the Nebula (condensation) theory? (More correctly known as the Solar Nebula Disc Model - SNDM).
Collapse of interstellar gas cloud to form a disc.
Collapse possibly due to the shock wave of a near by supernova or a merging with another cloud.
Rotational speed increases as cloud collapses under gravity.
Central portion collapses faster to form a protostar.
Elements with high melting points (stable at high temperatures) (refectory elements) condense near the sun.
Elements with lower melting points condense further away from the sun.
Condensed matter accretes under gravitational influence to form planetismals.
Planetismals collide to form planets.
Gas giants act like mini solar systems, but clouds of condensed icy material collapse to form central gassy planets and icy moons.
Problem!
Doesn’t explain angular momentum of planets.
Doesn’t explain how sun keeps 99% of the mass in the solar system.
Doesn’t really explain why and how planets orbit the sun in the same plane and direction.
What is the Modern Laplacian Theory?
Modification of Laplace’s Nebula Theory.
Cooling loud throws off gas rings as it spins.
Each gas ring forms a planet.
Composition of ring and the distance from the sun determines composition of the planet that forms.
Gas giants repeat process, throwing off own rings.
Ring formation explained by “supersonic turbulence” in early sun.
Throwing off gas rings can allow sun to retain most of mass in the solar system, but still have slow rotation.
Problem!
Gas rings may not last long enough to form planets.
What are the common themes in all theories of the formation of the solar system?
Sun and planets formed from contraction of gas clouds under own gravitational pull.
Rotation of cloud forms disc around central mass.
Central mass eventually becomes sun, rest of mass forms planets or is blown away when star switches on.
What happened immediately after the Earth was formed?
Earth was hit by a Mars - Earth sized planet, causing the outer crust to fall off the Earth.
The crust was caught in the Earths gravitational pull, to eventually condense and become the moon.
Solid inner core and liquid outer core contain the planet that hit the Earth.
Crust is thinner than it was supposed to be. This allows for plate tectonics to have formed.
Plate tectonics cause environmental stress, which causes natural selection and evolution.
