1. Earth Science Ch. 23
The Solar System

2. 23.1 Overview of the Planets
2 Groups of Planets
Terrestrial
Mercury, Venus, Earth, and Mars
Smaller, rocky, inner planets
Jovian
Jupiter, Saturn, Uranus, and Neptune
Huge gas giants, outer planets
Size is the most obvious difference between the terrestrial and jovian planets

3. Density Rate of Rotation Terrestrial planets have higher densities
Jovian planets are less dense because much of their volume consists of gas and ice
Rate of Rotation
Jovian planets have faster rates of rotation

4. Interiors of Planets Gases: hydrogen and helium
The materials that make up the planets are divided into 3 groups:
Gases: hydrogen and helium
Rocks: silicate minerals and metallic iron
Ices: ammonia, methane, CO2, water

5. Rocky and metallic substances Minor amounts of gases and ices
Terrestrial
Dense
Rocky and metallic substances
Minor amounts of gases and ices
Jovian
Less dense
Large amounts of gases and ices
Rocky and metallic materials found in the core

6. Atmospheres of Planets
Jovian
Very dense atmospheres of hydrogen, helium, methane, and ammonia
Maintain atmosphere due to large masses and colder temperatures which increase gravitational force
Terrestrial
Thin atmospheres due to warmer temperatures and smaller masses which decreases gravitational force

7. A gas molecule can escape from a planet if it reaches a speed known as escape velocity
Escape velocity depends on gravitational force
Larger gravitational force = larger escape velocity

8. Formation of the Solar System
Nebula
A cloud of gas and dust in space
A nebula often consists of 90% hydrogen, 9% helium, and a small percentage of heavier element

9. Nebular theory
The sun and planets formed from a rotating disk of dust and gases
Nebular material contracted due to gravity
Most of the material collected in the center
Remaining material formed a thick flattened rotating disk.
Within the disk the material cooled and formed grains and clumps of icy, rocky material

10. The growth of planets began as solid bits of matter collided and clumped together. This process is called accretion.
The accretion formed small irregular shaped bodies called planetesimals
The planetesimals grew larger as collisions and accretion continued
Once the planetesimals grew large enough to exert a gravitational pull they added more mass and became planets

11. The smaller inner planets formed because temperatures were so high that only metals and silicates could form solid grains. It was too hot for ices to form
The outer planets formed because it was cold enough for ices to form. Eventually the outer planets became so large that they could capture even the lightest of gases.

13. 23.2 Terrestrial Planets Mercury Orbital period: 88 days
Rotational period: 59 days
Planet closest to the sun
Slightly larger than Earth’s moon
Weak magnetic field which indicates a liquid core
Physical appearance is similar to the moon
Extremely hot because most solar energy is absorbed
No atmosphere to regulate temperatures
Greatest temperature extremes of any planet

14. Venus Orbital period: 225 days Period of rotation: 244 days
A day is longer than a year
Second planet from the sun
Second brightest natural object in the nighttime sky
Almost the same size as earth (earth’s twin)
Opposite rotation

15. Solid iron core and rocky crust similar to earth
Less craters than mercury but more than earth
Surface is shaped by basaltic volcanism and tectonic activity
Most of the surface is covered by volcanic flows
Densest atmosphere of the terrestrial planets
Extreme greenhouse effect
Most of the atmosphere is composed of CO2

16. Mars Orbital period: 687 days Period of rotation: 25 hours
4th planet from the sun
Half the size of earth
2 moons
Very old surface features
Many large inactive volcanoes
Home to the largest volcano in the solar system – Olympus Mons

17. Very thin atmosphere composed mostly of CO2 Contains polar ice caps
Very cold due to thin atmosphere
It is believed that Mars once had water at the surface. Most is underground now.
Evidence for surface water includes drainage patterns, evaporites, and geologic formations
The red color of Mars is due to the presence of iron oxide or rust

18. 23.3 The Outer Planets Jupiter Orbital Period: 12 years
Period of Rotation: 9 hrs. 50 min. (fastest)
Largest planet
Great pressure as you move toward the core which causes hydrogen gas to be changed into a liquid and then a metal.
Atmosphere contains hydrogen, helium, methane, ammonia, water, and sulfur compounds

19. Wind systems creates light and dark bands
Has a great red spot which is a giant wind storm
At least 64 natural satellites
One of the moons of Jupiter, Io, is very volcanically active.
Volcanic activity is caused by gravitational energy
Has rings

20. Saturn Orbital period: 29 years Period of Rotation: 10 hrs. 14 min.
Most prominent feature is the system of rings
At least 20 rings
Rings are composed of rock and ice particles
Very active atmosphere
Large storms
62 natural satellites
Titan is the largest moon
Only natural satellite to have a dense atmosphere and liquid water at the surface

21. Uranus Orbital period: 84 years Period of rotation: 17 hrs
Rotates on its side
Axis of rotation lies parallel with the plane of the orbit
Atmosphere contains mostly hydrogen, helium, methane, water, and ammonia
27 natural satellites
9 ring belts

22. Neptune Orbital period: 165 years Period of rotation: 16 hrs
Outermost planet
Extreme winds. One of the windiest places in the solar system
Great dark spot that disappeared and reappeared may be a giant storm
Cirrus like clouds found in the atmosphere
Ring system
13 moons
Triton is the largest and is the coldest body in the solar system

23. Pluto Orbital period: 248 years Rotational period: 6 days Dwarf planet
Pluto met 2 of the 3 criteria to be a planet:
Orbits the sun
Sufficient mass for its gravity to produce a round shape
Pluto is not considered a planet because it has not cleared the neighborhood around its orbit

24. Pluto is a dwarf planet. A dwarf planet meets the 3 criteria above and is not the satellite of another planet
3 satellites
Very elliptical orbit. At times during its orbit it is closer to the sun than Neptune
Largest moon is Charon

25. 23.4 Minor Members Asteroids
Orbit the sun in a belt between Mars and Jupiter
Larger than 10 meters in diameter
Orbital period of 3 to 6 years
Many of the most recent impact craters on earth and the moon were probably caused by asteroids
Possibly formed by a pre-existing planet or collisions among large bodies in space

26. Comets Composed of rocky and metallic materials
Held together by frozen water, ammonia, methane, CO2, and CO
Very elongated orbits that carry them beyond Pluto
Orbital periods can range from 100s to 1000s of years
The glowing head of a comet is called the coma
The coma is formed by solar energy

27. Comets originate in 2 regions of the outer solar system
The tail of a comet always points away from the sun because of radiation pressure and solar winds
Comets originate in 2 regions of the outer solar system
Kuiper belt: beyond Neptune, short orbital periods
Oort clouds: long orbital periods, form a shell around the solar system
Comet Halley: most famous (76 years)

28. Meteoroids
Shooting stars occur when a meteoroid enters earth’s atmosphere
Small solid particles that travel through space
Formation:
Interplanetary debris
Asteroid belt material
Remains of a comet

29. Meteorites can be made of iron or silicates (stony)
Meteors
Meteoroids that enter earth’s atmosphere and burn up
Meteor showers are composed of materials lost by comets
Meteorites
meteoroids that reach the earth’s surface
Meteorites can be made of iron or silicates (stony)
Scientists have used evidence from meteoroids to estimate the age of the solar system (4.5 billion years)