Origin of the Solar System Part 1: Solar System Survey and Testing the SNT
1. For the Solar Nebula Theory (SNT), what must it explain?
For the SNT to be successful, it must successfully explain all the phenomena we encounter in our
solar system. If the mechanisms on which it depends fail to do so, then, like Laplace’s, Buffon’s, and
Descartes’ theories, it will be replaced by a theory that is more robust – more predictive.
2.
How is the fact that the planets revolve around the sun in a common plane support for the Solar
Nebula Theory?
Because the SNT states that the solar system formed from a flattened nebular disk of gas and dust.
If the planets were not in the same plane, then that would be important evidence against the SNT.
3.
In what direction do all planets revolve and in what direction do most of the planets rotate?
What are the exceptions? Conjecture as to how the exceptions might have occurred.
All of the planets revolve counterclockwise around the sun and almost all of the planets and the sun
rotate counterclockwise on their axes. The two exceptions to this rule, Uranus and Venus, were
probably rocked by a collision which altered their rotations.
4. How does the existence of two types of planets in our solar system provide evidence supporting
the SNT? How does the “frost line” affect where the two types of planets formed?
The frost line is the point at which materials, which are gases in the inner solar system, are able to
freeze and become ice due to very low temperatures. The SNT predicts that, based on temperature
(distance from the sun), there should be two types of planets. In the inner solar system, the planets
should be rocky (due to the condensation of metals and silicates) and dense, while the planets
beyond the frost line should be less dense (made up of hydrogen compounds) and much more
massive.
5. What are the primary distinctions between the two types of planets? What are the similarities, if
any?
The inner planets are rocky, small, and dense worlds made up of condensed metals and silicates. The
outer planets are massive, have liquid or ice interiors, and are low-density. In addition, the Jovian
planets have lots of moons, all have rings, and their atmospheres are turbulent with “great” storms.
All of the planets have been marked by collisions with space debris (and possibly other planets in
their remote past.
6.
Besides planets, what are some of the other, smaller, bodies (also referred to as space debris)
that share our solar system? What evidence do they contribute to the SNT?
Smaller bodies such as comets, asteroids, and meteoroids also are found our solar system.
Asteroids are small rocky “worlds” that are the result of a failed planet between Mars and Jupiter.
The planet failed to coalesce due to Jupiter’s gravitational force. Most orbit the sun between Jupiter
and Mars, though there are a significant number that stray into the inner solar system and represent
collision risks.
Comets are small (up to 10km in diameter), ice-rich bodies (also called dirty snowballs) that are
leftovers from the period of planet formation. They are evidence that the solar nebula had abundant
icy material.
Meteoroids are small bits of rock and metal that occasionally enter our atmosphere – then we call
them meteors (meteorites if they actually make it to earth). Meteorites have given us the
opportunity to age the solar system since they are also leftovers from the solar system’s formation.
7. Where are craters found in the solar system? What is the significance of their existence to testing
the SNT? What do they tell us?
Craters are found on all surfaces in the solar system that are strong enough to retain them (i.e. the
terrestrial planets). When astronomers see a rocky or icy surface with few craters, they know that
the surface is new. For example, the moon and Mercury are very old surfaces – they are marked with
craters – while Europa and the Earth show far fewer craters. Earth’s and Europa’s surfaces are, due
to geological forces, relatively new. The craters also give us insight into how the early solar system
would have been formed by collisions.
8. What is the Kuiper Belt and where is it found?
In 1992 >1,000 small, dark, icy bodies orbiting the outer fringes of the solar system, beyond Neptune,
were discovered by Gerard Kuiper. The dwarf planet Pluto is the largest object in the Kuiper Belt.
The Kuiper Belt is found out beyond the orbit of Neptune and is still little studied. The NASA mission
New Horizons will be arriving to Pluto and the Kuiper Belt in 2015.