Origins and Our Solar System

The Solar System

The 8 planets form 2 different families. The four closest to the Sun represent

the terrestrial planets – Mercury, Venus, Earth and Mars.

The four farthest from the Sun are sometimes referred to as the gas giants, the Outer Planets, the Jovian planets – Jupiter, Saturn, Uranus, Neptune.

The Families Differ

The families differ in the compositions of their cores and atmospheres.

Terrestrial planets have ____________ Surrounding the inner ______ core is a

outer core of silicates (rocks) Range in a diameter of 4880 km –

12800 km

The Outer Planets

Enormous when compared to the Terrestrial planets.

Jupiter is the largest with diameter of 143,000 km, Saturn 121,000 km, Uranus 51,000 km, Neptune 49,500 km

The Outer planets also have cores composed of Ni and Fe, but the vast majority of their enormous mass is from Hydrogen or hydrogen compounds such as Methane.

The Outer Planets

Because of their HUGE masses the gravitational pull is very great.

Due to the low temperature and pressure these compounds are in liquid form.

Besides hydrocarbons the most common element is Helium other elements such as N, and S are also present.

Even though there is such great variation between the planets the elements that we find on all the celestial bodies are similar.

The commonality of elements that are found on all the planets, moons, asteroids and celestial bodies leads us to ask the question: “How did they all get here?”

Theories Regarding the Origin of the Solar System

Catastrophe Theories –

(also called the planetesimal hypothesis or condensation theory) – Before the Sun and planets were formed, the material that became the Solar system was part of a large diffuse cloud of interstellar gas and dust comprised of H and He. The nebula became unstable and started to collapse in on itself because of gravity.

Origins of the Solar System – Solar Nebula Theory (cont.)

The center of the Nebula became the Sun as Temperature and pressure increased and thermonuclear reactions began.

As the Sun rotated and the presence of a weak magnetic field, the nebula began to flatten to form a disc with the Sun in the center.

As Temperatures decreased material cooled and condensed from a gas to a solid.

Due to the high temperature closer to the Sun different elements solidified. This caused the differing amounts of Fe and Ni in the cores of the Terrestrial planets and the Jovian planets.

Origins of the Solar System – Solar Nebula Theory (cont.)

The grains of elements collided with each other and formed larger and larger pieces.

were formed – small moon sized planets that then formed the terrestrial planets.

(small planets that coalesced into the Jovian planets) were formed in the outer solar system because temperatures were much colder and allowed gases like He and H to solidify and become parts of the larger Jovian planets.

Some Evidence Supporting the Nebula Theory

Components of the Solar System

– A star composed of 71% Hydrogen and 21% Helium. Contains small amounts of every other element in vaporous form.

Ball of H and He that generates light because of nuclear reactions in the core

Largest body in the Solar System 700x the mass of everything else combined.

More about Stars later

The Terrestrial Planets

We will discuss the different planets in the future chapters.

Basic information regarding the two families:

Terrestrial = Composed of rock Rock – Silicates, which have a mix of Oxygen

and Silicon as well as other heavier elements. Distinct solid “ground” If there is an atmosphere, it is gaseous.

Terrestrial planets

The Outer Planets - Jovian

Jovian Planets = composed of ice Ice – frozen liquids and gases.

Examples: water, Carbon Dioxide, ammonia, and methane

All have a ring system No distinct boundary between crust and

atmosphere. As you go deeper into the planet the

gases become more dense, may turn into liquids, and possibly a solid core.

The transition is not sharply defined

The Jovian Planets

Satellites

Every planet in the solar system EXCEPT Mercury and Venus has at least one satellite (moons).

As we send more probes to the outer planets, more moons (satellites) have been discovered Planets # of Moons

Jupiter 39 Saturn 30 Uranus 21 Neptune 8 Mars 2 Earth 1 Pluto 1

Answer the questions in your notes. I will come around to check

What is the relationship between planetary size and the number of moons?

Can you hypothesize why Venus does not have any moons? Please provide 2.

Asteroids

– Rocky or metallic bodies ranging in size from a few meters to 1,000km in diameter.

Most asteroids are located in the asteroid belt located between Mars and Jupiter.

The asteroid belt circles the Sun and is most likely materials that would have coalesced into a planet, but Jupiter’s gravity prevented it from occurring.

Comets

Comets – Icy bodies about 10 km in diameter. A tail of gas and dust extends off the comet as it vaporizes when it nears the Sun.

Most comets are located far beyond the object once known as Pluto in an area called the Oort Cloud, which is a spherical region 40,000-100,000 AU from the Sun.

If a comet doesn’t originate in the Oort Cloud it probably came from the Kuiper Belt. Which is a disk shaped area beyond Neptune. Pluto and its satellite are most likely Kuiper belt objects that “escaped” the belt.

Bode’s Law

A numerical expression for approximate distances of most of the planets from the Sun.

Yet to be explained, each planet is (VERY ROUGHLY) about twice as far from the Sun as its inner neighbor.

We are unsure if this is just a major coincidence or a physical property affecting Solar system formation.

Odds and ends of the chapter

Age of the solar system: 4.5 billion years old. The outer planets’ composition is similar to

the Sun. The inner planets lack some gases that only

form solids at VERY low temperatures (this does not include the atmospheres of the planets)

The solar system developed from the solar nebula- the rotating disk of gas and dust from which the Sun and planets formed. (imagine a spinning pizza crust).

Odds and ends of the chapter

Condensation – when a gas cools enough to form a solid or a liquid.

There are various theories regarding when and how the different moons were formed

Other planetary systems

There are other stars with planets orbiting them.

Planets orbiting another star are called extra-solar planets.

Difficult to see because they are small and any light they reflect is often “drowned out” by the light of their sun.

Figure 7.12 lists some of the known extra-solar planets.