The Structure & Origin of the Solar System

In this section, the notes describe …

1.The Sun2.The structure of the solar system 3.The appearance of the Moon in the sky and related phenomena like eclipses and tides4.The origin of the solar system

However, this presentation will focus on •The properties of the Sun, and•The basic tenants of Solar Nebula TheoryFor the rest of the concepts in this sections, please see the online notes.

The Sun - The central star (body) of our solar system.•It powers our planet and makes life possible.•It is approximately 8 light minutes away. (1.5x108 km, or nearly 93 million miles)

(Always use caution when viewing the Sun. Never use unfiltered telescopes, binoculars or cameras to observe the Sun!)

The Sun

The Photosphere – “Light” Sphere

The effective surface of the Sun.

It is the layer from which most of the Sun's light is emitted.

It is approximately 106 miles in diameter,

It has a temperature of ~ 5800 K.

Note: the Sun doesn't end here!

The Chromosphere – “Color” Sphere

The thin (~ 10,000 km) layer of the Sun's atmosphere just above the photosphere.

This layer glows with a pinkish light, due to hydrogen emission.

It can only be seen during a total eclipse or with special filters.

The Corona – Latin for Crown

Corona - The uppermost level of the Sun's gases.

It is visible as a "halo" around the Moon during a total solar eclipse.

It is extremely hot, ~ 106 K!

It emits mostly x-rays.

The Sun’s AtmosphereThe PhotosphereThe Chromosphere

The Corona

European Southern Observatory

The Solar Wind

Stream of charged particles (protons, electrons, alpha particle, etc.) released by the Sun as the corona continually

expands into space.

Particles from the solar wind interact with the Earth and cause magnetic disturbances and the Aurora.

The solar wind stream can be enhanced by either: 1.Solar Flares (which trigger coronal mass ejections, or CME’s)

2.Coronal Holes

These phenomena on the Sun cause stronger geomagnetic storms on earth and lead to greater Auroral Activity

Sunspots

Sunspots are dark, relatively cool spots visible on the surface of the Sun.

Their temperatures are about 4500 K as compared to the

5800 K temperature of the photosphere.

These spots are associated with strong magnetic disturbances on the Sun, and are dark because they

suppress the Sun's convective flow.

Sunspot groups are often the locations for strong solar activity, including solar flares.

The darkest central region of sunspot groups are called the umbra.The lighter surrounding regions are known as the penumbra.

Sunspots

•Umbra

•Penumbra

High Resolution Image of a Sunspot Group

From CSU’s Mead Observatory

Solar Flare on July 15, 2002

Photographed by Shawn & Christian Cruzen

CSU’s Mead Observatory

Large Coronal Mass Ejection

Caused by a solar flare on the Photosphere.

Aurora Borealis 4-6-00 Randy & Betty Ivins – Taken in Manchester, GA

Aurora Borealis 11-20-03 Randy & Betty IvinsTaken in Manchester, GA

Origin of the Solar System

Cosmogony - The study of the origin of the solar system.

Theories or models must take into account the many characteristics and regularities in the solar system.

Solar System Regularities:1. The planets' orbits are almost circular.2. The planets' orbits lie nearly in the same plane. (Ecliptic)3. All the planets revolve in the same direction around the Sun - counter clockwise as viewed from north.4. The Sun rotates in the same direction.5. Almost all the planets rotate in the same direction. (Exceptions?)

6. Some of the planets have families of satellites that revolve around them in a manner similar to the planets around the Sun.

Models of Cosmogony must also account for:1.The spacing of the planets' orbits

2.The distribution of sizes

3.The composition of the planets.

Early "Possible" Models:1.Catastrophe Theories: The Sun collided with another star or other large

body and created the planets.2.Tidal Theory: A passing star gravitationally pulled the material out of the

Sun and formed the planets.3.Capture Theory: The Sun’s gravity captured passing planetary bodies.

3.Theoretical Calculations: show that material drawn out of the Sun or ejected in a collision would disperse rather than form planets by

condensation.4.Also, only by a few "solar systems" would form in a galaxy by the above

models since collisions and near collisions are rare!5.Recent observational evidence suggests that "solar systems" are

common. (At Least 560!)

Solar Nebula Theory

Solar Nebula Theory

The Nebular Hypothesis: The beginnings of this model

(Nebula – gas cloud in space)

•Proposed separately by Immanuel Kant (in 1755) and Pierre-Simon Laplace (in 1796)

•The sun and planets formed a spinning cloud of gas; the Primeval Solar Nebula.

The mechanism that caused the collapse (maybe a supernova) would give the cloud a net spin.

I. In the plane of rotation, spin works to counteract gravity.

II. In the other dimension, gravity collapses the clouds into a disk (plane) with a net spin

direction. (revolution & rotation).

Solar Nebula Theory

Protosun: The sun in formation; no nuclear

fusion, yet.

Planetesimals: objects ~ 102 km across which

formed from interstellar dust by clumping. (sticking together, then gravity).

Protoplanets: accreted out of planetesimals after ~ 107

years.

The sun condensed and fusion reactions turned on ~

105 years.

Planets not massive enough for fusion to initiate.

Protoplanets either: 1. Condensed to form planets

2. Collided with other protoplanets and were absorbed

3.Were captured by planets to form moons. (most moons simply accreted in mini-solar systems.)4.Were ejected from our Solar system by gravtational interactions

Collisions with planetesimals may have: 1. Fragmented and stripped off the outer layers of Mercury.

2. Slowed Venus’s rotation.

3. Tipped Uranus on its side.

4. Formed the moon from the Earth.

• Lighter elements were probably blown to the outer solar system by violent solar winds (T Tauri winds) from the young

Sun.

•Billions of unused planetesimals may have become comets.

• Temperature decreased with distance in solar nebula. This effected composition of planets.

•e.g. Little or no ice or volatiles on terrestial (inner) planets •Plenty of ice and volatiles where the gas giants formed

•Terrestrial ices and atmospheres were probably enhanced by later comet impacts!

•Evidence of this process of solar system formation has been observed elsewhere in our galaxy.

Examples: Beta Pictoris; Protoplanetary Disks in Orion Nebula

Protoplanetary Disk around Beta Pictoris

Protoplanetary Disks in Orion Nebula