The Structure & Origin of the Solar System
In this section, the notes describe …
1. The Sun
2. The structure of the solar system
3. The appearance of the Moon in the sky and related phenomena like
eclipses and tides
4. The origin of the solar system
However, this presentation will focus on
• The properties of the Sun, and
• The basic tenants of Solar Nebula Theory
For 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
Corona
The
Sun’s
Atmosphere
The
Photosphere
The Chromosphere
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 Ivins
Taken 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.
• Theoretical Calculations: show that material drawn out of the Sun or
ejected in a collision would disperse rather than form planets by
condensation.
• Also, only by a few "solar systems" would form in a galaxy by the
above models since collisions and near collisions are rare!
• 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