14-02-2013, 11:49 AM
Origin of the Solar System
Origin.doc (Size: 56.5 KB / Downloads: 24)
Introduction.
The basic premise in the understanding of our origins, and the properties of all the planets we have studied this term, is that natural forces created and shaped the Solar System. And that there is continuity to that process, i.e. it is not a sequence of random events.
Any model or theory for the formation of the Solar System must have a set of explanations for large-scale and small-scale properties.
Large-Scale:
1. the planets are isolated in orderly intervals
2. orbits are nearly circular
3. orbits are in the same plane
4. all planets revolve prograde
Small-Scale:
1. most planets rotate prograde
2. the systems of moons can be divided into regular objects (spherical) with direct orbits versus irregular objects with eccentric orbits
3. terrestrial planets have
i. high densities
ii. thin or no atmospheres
iii. rotate slowly
iv. rocky, poor in ices and H/He
4. Jovian worlds have
i. low densities
ii. thick atmospheres
iii. rotate rapidly
iv. many moons
v. fluid interiors, rich in ices, H/He
5. Most of outer SS objects (not just Jovian worlds) are ice-rich
Also note that the overall architecture of our Solar System is orderly and the ages of its member’s uniform. All indicators point to a single formation event about 4.6 billion years ago.
The above is not to ignore the fact that a great deal of evolution occurred in the Solar System after it formed (see below). For example, the origin secondary atmospheres of the terrestrial worlds underwent a large amount of chemical processing (Venus was baked, Mars was frozen, Earth developed life). There was also orbital evolution as well, rings were formed, moons captured, tidal locking between worlds (e.g. Pluto and Charon). So the Solar System is not a static system, it is dynamic.
How does one test a hypothesis?
To answer scientific questions requires the formulation of a hypothesis. The hypothesis is tested against the facts to look for contradictions that rule out or require modification to the hypothesis. Note that the process of hypothesis formulation and then theory building is a lengthy, career dependent operation. So the sociology of science requires that a hypothesis be tested and confirmed by many scientists since the creator of the hypothesis has a strong psychological attachment to his work.
Encounter Hypothesis:
One of the earliest theories for the formation of the planets was called the encounter hypothesis. In this scenario, a rogue star passes close to the Sun about 5 billion years ago. Material, in the form of hot gas, is tidally stripped from the Sun and the rogue star. This material fragments into smaller lumps which form the planets. This hypothesis has the advantage of explaining why the planets all revolve in the same direction (from the encounter geometry) and also provides an explanation for why the inner worlds are denser than the outer worlds.
However, there are two major problems for a theory of this type. One is that hot gas expands, not contracts. So lumps of hot gas would not form planets. The second is that encounters between stars are extremely rare, so rare as to be improbable in the lifetime of the Universe (15 billion years).
Nebular Hypothesis:
A second theory is called the nebular hypothesis. In this theory, the whole Solar System starts as a large cloud of gas that contracts under self-gravity. Conservation of angular momentum requires that a rotating disk form with a large concentration at the centre (the proto-Sun). Within the disk, planets form.
While this theory incorporates more basic physics, there are several unsolved problems. For example, a majority of the angular momentum in the Solar System is held by the outer planets. For comparison, 99% of the Solar System's mass is in the Sun, but 99% of its angular momentum is in the planets. Another flaw is the mechanism from which the disk turns into individual planets.
Protoplanet Hypothesis:
The current working model for the formation of the Solar System is called the protoplanet hypothesis. It incorporates many of the components of the nebular hypothesis, but adds some new aspects from modern knowledge of fluids and states of matter.
Meanwhile in the inner Solar System:
Note that as the planets began to form they grew in mass by accreting planetesimals. Since force of gravity is proportional to mass, the largest planetesimals are accreted first. The early proto-planets are able to sweep the early Solar System clean of large bodies.
CONCLUSION.
The basic premise in the understanding of our origins, and the properties of all the planets we have studied this term, is that natural forces created and shaped the Solar System.
Any model or theory for the formation of the Solar System must have a set of explanations for large-scale and small-scale properties.
Also, the overall architecture of our Solar System is orderly and the ages of its member’s uniform. All indicators point to a single formation event about 4.6 billion years ago.
Moreover, the planets in the solar system are divided into terrestrial and Jovian/Exterrestrial planets and are different in their position, composition and other features and each feature makes each of them unique in its character.