Earth
•Earth Stats:
•Radius = 6378 km
Mass = 6 x 10 24 kg
Density = 5.5 g/cm 3
•Knowledge of the Earth's interior comes from seismology - the study of ground vibrations.
•Seismic waves can be reflected and refracted at boundaries, just like light waves. Using this fact, and other evidence, geologists have modeled the Earth's
Interior.

Earth
Above: Sumatran Earthquakes, April 2012, recorded at the
CSU’s Coca-Cola Space Science Center

Earth
Earth's structure has three primary layers.
•
•
The Core
• About twice the size of the Moon, ~ 3400 km in radius.
Composed mostly of iron & nickel
The inner portion is solid. ~ Moon-sized.
•
•
The outer portion is liquid (very dense).
Convection + rotation = Dynamo effect - Magnetic field
The inner core rotates slightly faster than the outer core. This may contribute to changes in Earth's magnetic field.

•
•
•
Earth
The Mantle
• Layer of composed of dense rock and metal oxides.
The mantle behaves as a plastic - properties of a solid but can flow under pressure.
It is ~ 2900 km thick.
Contains 65% of Earth's mass! (Density ~ 3.5 - 5.8 g/cm 3 )
•
•
The Crust
• A thin layer of silicates - granite(quartz) & basalt(feldspar)
Has a relatively low density, 2.5 - 3.5 g/cm 3
Is only between ~ 10 km & 70 km thick

Earth
Isotopes - atoms of an element with the same properties but different masses (more neutrons)
Some isotopes are unstable and decay radioactively, releasing energy.
Earth's interior is heated by radioactive decay.
Core temp. = 7500 K, hotter than the Sun's surface!
Differentiation - process by which a homogeneous body becomes stratified.
This process gave Earth its layered structure.

Above: Image of
Earth and Moon together from
NASA's Mars
Reconnaissance
Orbiter

Earth
As the Earth was heated, it became molten.
Heavier (more dense) elements sank.
Lighter (less dense) elements rose.
Tides - result from differences in gravitational force depending on distance. Tidal forces are differential forces.
Aurora Borealis - Charged particles guided by Earth's magnetic field toward the North Pole, which hit our atmosphere causing it to glow. Northern Lights: Aurora Australis - southern lights
Magnetosphere - region around the Earth in which the magnetic field keeps out charged particles flowing from the
Sun.

The Moon
•Moon Stats:
Radius 1738 km = R m
Mass 7.4x1022 kg = M
= ¼ R
E m
= 1/81 M
E
Density 3.34 gm/cm 3 = D m
(g
M
= 1/6 g
E
)
•Albedo - ~6%
•Lunar Temperatures: 265 F in sun and -170 F in shade!

Hadley
Rille

The Moon’s Features
•Highlands: ancient, heavily cratered terrain on the moon with higher average elevation.
•Maria: lowlands; large, flat, relatively crater-free plains on the moon. (singular = Mare) Younger terrain. (Latin = “Seas”)
•Mountain Ranges and Valleys: Formed by impacts and debris, not by tectonics as on Earth.
•Crater: circular depression caused by an impact.
• Some lunar craters ~ 300 km across!!!
• Deeper than Grand Canyon!!

Mountain Range
Lunar
Highlands
Mare or “Sea”
Rayed Crater

The Moon
•Terminator: line separating day from night.
•Features more easily observed near the terminator.
Longer shadows!!
•Lunar interior is differentiated.
1.
It has a core with little or no iron (no magnetic field).
2.
It has a large mantle where moonquakes occur.
3.
It has a thick crust ~ 12% of its volume.

The Moon’s Origin
Giant Impact: A Mars-sized impactor hit the proto-
Earth off-center. Lighter debris from the impact was scattered into orbit and coalesced to form the Moon.
• Explains the Moon’s small iron core
•
•
Explains the similarities AND the differences in isotope abundances
Any volatiles would have been driven off the
Moon by the heat of the collision.
• Collision is consistent with the present angular momentum of the Earth-Moon system.

Mercury
•Mercury Stats:
Radius: 2439 km = 0.38 R
Mass: 0.055 M
E
(5.5% M
E
Density: 5.43 g/cm 3
Eccentricity of Orbit: 0.206
)
E
Average distance from the sun: 0.40 AU
Maximum angle from the sun: 28 degrees
• Thus, the sun always rises or sets within ~ 2 hours of Mercury.
• Mercury always viewed in twilight or daylight or through thick turbulent air!

Mercury
•The sidereal rotation period to be ~ 59 days.
•The revolution period is 88 days. (88/3 = 29.3)
•This is a 2:3 relationship.
•Albedo – the fraction of sunlight hitting a planet that is reflected.
•The albedo of a planet can be compared with the albedos of materials on Earth to determine of what material the surface of the planet is made.
•Mercury and the moon both have low albedos ~ 6%.

Mercury
•Mercury has a large core: Made of iron
~ 42% of its volume
~ 70% of its mass
• Mercury undergoes the greatest surface temperature variations in the solar system: during the day 427 C (800 F) at night -183 C (-300 F)
•Mercury has almost no atmosphere.
•Mercury has no moons.

Mercury
•Mercury’s Surface:
1.
Heavily cratered in general
2.
Has large, smooth plains (like Maria)
3.
Has heavily cratered terrain (like Highlands)
4.
Has lightly cratered intercrater plains in between.
•Mercury has very long scarps – lines of cliffs formed as Mercury’s core cooled and shrank – “wrinkles.”
(Much longer than on the moon).
•Caloris Basin: 1300 km wide impact plain (like Mare
Imbrium) bounded by 2 km high mountains.

Image from
MESSENGER
Spacecraft

Mercury
•Mercury has a very slight atmosphere, consisting of
Hydrogen, Helium (from the sun – solar wind), oxygen, argon, sodium and potassium (Sodium is the major constituent of Mercury’s atmosphere) Both sodium and potassium are found because of
“sputtering” by solar wind).
•Mercury has a magnetc field = 0.1% BE – a partially molten core.

Venus
•Earth’s “sister” planet
•“Evil step sister” --Dr. C.
•Approximately equal sizes masses and densities.
•Venus Stats
Radius – 6,052 km ~ 0.95 R
E
Mass – 0.82 M
E
Density – 5.24 g/cm 3
Orbital Period – 225 days (sidereal!!)
Rotational Period – 243 days (retrograde!) (sidereal!)
Ave. Orbital Radius: 0.7 AU
Surface Temperature: ~ 900 F (would melt lead!!!)

Venus
• Spectra reveal the composition of the atmosphere: carbon dioxide ~96% (<0.1% on Earth); nitrogen nearly 4% with 0
2 and <1.0% H
2
0
•Atmospheric pressure ~ 90 * P atm -E
(due to CO
2
)
•Where’s the CO
2 on Earth?
It mixed with rain and minerals to form rocks such as limestone. Some organisms aided in this process. It is also trapped in our ocean waters.
•Venus has no oceans and no life; CO
2 is free!

Venus
• What happened to Venus’s H
2
O “Oceans”?
•A.
Closer to the sun
•B.
Lower atmosphere; hotter
•C.
More water vapor rose to the upper atmosphere
•D. Solar UV broke it into H & O
•E.
H is very light and easily escaped into space!!
•F.
O combined with other gasses or with iron on the surface

• Clouds of Venus contain some H
2 but much H
2
SO
4
– Sulfuric Acid
O
•Surface Temperature: intensity of emitted radiation increases with surface temperature (black body radiation)
• Radio waves penetrate Venusian clouds. Radio intensity yields surface temperature 900 F!!
•“Runaway Greenhouse Effect”
•Heat energy, released as I.R. is “trapped” by a nearly opaque atmosphere.
•Surface temperature must climb very high before escaping I.R. = (balances) incoming visible energy.

Red

• MARS STATS
Radius – 3397 km ~ 0.53 R
E
Surface Temperature -- -190 F to 80 F
(~ 1/10 M
E
Mass – 0.11 M
E
)
Density – 3.94 g/cm 3 (Mars has a much smaller core and thicker crust than Earth!)
Orbital Period – 687 days
Rotational Period (sidereal) – 24 hrs. 37 min.
Ave. Orbital Radius -- ~ 1.5 AU (semimajor axis
= 1.523 AU)
Tilt of the Axis – 25 degrees (Thus, Mars has similar seasons! Four seasons twice as long as
Earth’s)
Mars’ atmosphere ~ 1% P atm
E . Mostly CO
2

?
.

• Groundwater erodes away the topsoil forming an alcove .
• Water gushes downhill from the alcove cutting a channel , and clearing it of debris.
• Material swept out by the water forms an apron debris at the bottom of the formation.
of

Mars has two Moon.
• *Phobos (27 km across) orbits 7h 40 min.
albedos ~ 6%
• *Deimos (15 km across) orbits ~ 30h albedos ~ 6%

In the inner solar nebula, condensation of volatile elements was not possible because of the high temperatures.
Only dust grains of metals, silicates, oxides, etc., were able to survive.
But Jupiter (5.4 AU) is 5 times and Saturn (9.4 AU) is
10 times further from the Sun than is the Earth.
Temperatures were much lower in this part of the solar nebula.
Thus, volatile elements, including hydrogen & helium
(the most abundant) became more important constituents of these planets.

The Jovian planets probably formed in two steps:
1. Dust grains, coated with frozen gasses, accreted quickly to form 4 large protoplanets, each several times more massive than the Earth.
2. The strong gravitational attraction of these protoplanets accreted and retained large amounts of hydrogen, helium and other volatile elements.
Rotation
All of the gas giants rotate in less than 18 hours!
Jupiter, the largest planet in the solar system, rotates in less than 10 hours!
(About 9 hr 55 min).
This rapid rotation makes the Jovian planets more oblate

The Jovian planets experience differential rotation – different latitudes rotate at different rates.
Example: Jupiter
Near the poles 9 hr 55 min
Near the equator 9 hr 50 min
This differential rotation contributes to the banded appearance of the Jovian atmospheres.
Belts and Zones – More easily visible on Jupiter and Saturn.
Zones – bright bands; rising gas; the tops are approximately
20 km higher than the belts; ~ 10K colder than the belts.
Belts – dark bands; falling gas; lower than the zones (thus, about 10K warmer – getting ready to rise up again!).

Jupiter Stats
Radius ~ 71,500 km ~ 11.2 R
E
Mass ~ 318 M
E
Revolution ~ 11.9 years
Jupiter has at least one dark ring.
Jupiter has at least 17 moons, including the 4 Galilean satellites – Io,
Europa, Ganymede & Callisto
Io very few impact craters  young surface
• hundreds of volcanic calderas – many are active
• sulfur dioxide plumes erupt 300 km high!

Europa
• very smooth surface; only a few hundred meters variation in altitude  very young surface.
• Photographs of the surface resemble images of sea ice on Earth.
• There may be liquid H
2
O under the icy surface; 20 km – 50 km deep
Comet Shoemaker-Levy 9
• Collided with Jupiter in 1994 - Original body was 2 – 10 km in diameter.
• It was broken into 21 fragments by Jupiter’s gravity - Largest fragments 1 – 3 km in diameter.
• 1st time a collision between extraterrestrial bodies was “observed” by astronomers.
• The Great Red Spot of Jupiter – A high-pressure, anti-cyclone (rotates counter-clockwise in the Southern Hemisphere) that protrudes above the surrounding cloud tops.The Red Spot is about 12,000 km by 25,000 km (~ 2.5 to 3 D
Earth
) & has lasted for more than 300 years!

•The beautiful rings are easily visible
•Notice the gap in the rings - Cassini Division
•The shadow of the rings on the planet can be seen
•As many as six moons can be seen, including Titan

Radius ~ 60,300 km ~ 9.4 R
E
Mass ~ 95 M
E
Rotation ~ 10 hr 40 min
Revolution ~ 29.4 years
Saturn has thousands of tiny ringlets; combined they form the rings.
Particle size ranges from 10 -2 m to 10 m (a few km sized).
Saturn’s moons include Titan, second largest moon in the solar system.

Radius ~ 25,600 km ~ 4.0 R
E
Mass ~ 14.5 M
E
Rotation ~ 17 hr 14 min
Revolution ~ 83.75 years
Semimajor Axis ~ 19.2 AU
Uranus has (at least) 9 rings. Discovered by Occultation

Radius ~ 24,800 km ~ 3.9 R
E
Mass ~ 17.2 M
E
Rotation ~ 16 hr 7 min
Revolution ~ 163.7 years
Semimajor Axis ~ 30.1 AU
Neptune has at least 3 rings. Discovered by Voyager
Neptune’s Great Dark Spot:
• Half the size of Jupiter’s Great Red Spot
• Photographed in 1989 by Voyager 2