The Planets of the Solar System



The Inner Planets



The Earth/Moon system (a separate file)


The Outer Planets







The Inner (Terrestrial) Planets


The innermost planet

One of the brightest objects in the sky

But rarely seen - WHY? (Never more than 28 deg. from the sun)

Fastest moving of the planets (named for the Greek & Roman God of Speed)

Orbits sun in 88 earth days at 48 km/s

Orbit is most varied of all planets (except Pluto)

Highly eccentric (0.206)

Perihelion: 46 million kilometers

Aphelion: 70 million kilometers

Also, inclined 7 deg. to plane of ecliptic

Very small, but with a similar density to earth (5.5)

Seems to be similar in composition to earth, but different proportions

Core accounts for 60% of its total mass (fig 13.22, pg. 230)

Basically a small metal ball with a thin silicate crust

Surface features

Quite a range of temperatures

Up to 400 deg. C at 'noon'

Proximity to sun supplies the daytime heat

Drops to -175 deg. C just before dawn

Lack of atmosphere allows the heat to escape at night

This would give your heat pump a real workout

Heavily cratered like the moon

With areas that have been flooded by basalt

Volcanics very early in planets history (4 b.y.)

No evidence of plate tectonics

Isolated 'scarps' indicate shrinkage during cooling (fig. 13.25, pg. 232)

General tectonic history indicates:

Early expansion while hot

Releasing basaltic flows

Later shrinkage during cooling

Causing scarps due to compression/contraction



Very similar to earth on overall features

Physical features nearly identical (Table 15.1; pg. 258)

Surface is only lightly cratered

Dominated by volcanic activity

Definite "continents" as on earth (2 of them)

Indirect evidence for surface water in the past

One difference is its retrograde rotation

"One of the most beautiful objects in the night sky"

Named for the Goddess of Love and Beauty

Beauty is clearly "only skin deep" because its a rather ugly place at the surface

Extremely harsh surface conditions

Temperature well above 400 deg. C

Atmospheric pressure 90X that of earth (we would implode!)

Both the result of the extremely dense atmosphere (96% CO2)

Thick cloud cover is the result of H2SO4 droplets in the atmosphere

Probably derived from extensive volcanic activity

Greenhouse effect

DIGRESS TO: runaway greenhouse effect

Venus used to be more like Earth

Almost certainly had large amounts of surface water

Initial slow surface heating due to small increase in atmospheric CO2

Leads to increased evaporation and H2O content in air

Leads to more heat retention, and the "Runaway Greenhouse Effect" cycle

Carried to its logical conclusion...

Leads to evaporation of any surface waters and a "hot water" atmosphere

Water vapor is not stable in UV light and breaks down into atomic form

Hydrogen escapes into space

Oxygen combines with iron, etc. at the surface

Therefore, the loss of surface water is permanent

Could this happen on the earth?



The "red planet" named for the God of War

Much smaller than the earth

Approx. 11% earth's mass

Atmosphere similar to Venus in composition (95% CO2)

But not in density - .006 bar (Mars) to 1 bar (Earth) to 90 bar (Venus)

Surface similar to earth 200 mya when Pangea was complete

Southern highland (continent) which is heavily cratered (probably older)

Surrounded by younger volcanic plains (not covered by water)

Several kilometers lower in elevation than the "continent"

Extensive tectonic and volcanic activity

No direct evidence of plate tectonic activity

Several features indicating tectonic/volcanic activity

Most 1-3 billion years old

Tharsis Bulge - active region the size of North America

Concentration of "recent" volcanic activity

Olympus Mons (fig. 14.8, pg. 241)

Probably largest volcano in solar system (fig. 15.14, pg. 268)

Possibly still intermittently active!

Valles Marineris (fig. 14.10, pg. 243)

A tectonic feature so not really a "valley"

Basically tension cracks on the edge of the Tharsis Bulge

Similar to tensional features in Africa

Big! 5000 km X 100 km X 7 km deep

Possibly plate-style activity may have started long ago

Did not develop like on earth due to smaller mass, quicker overall cooling

Much evidence for surface water (See: photo pg. 234; fig. 14.8b, pg. 241)

Most drainage features limited to older cratered highland areas

Two kinds of drainage patterns

Normal dendritic patterns (fig. 14.12, pg. 244)

Developed on the older cratered upland areas

Evidence for catastrophic floods (fig. 14.21, pg. 250)

From the upland onto the lava plains

Like the Channeled Scablands of Eastern Washington

Evidence for glacial ice ages in the Martian past?

Supports theory that surface water was present during 2 periods in the past

The first 4 billion years ago related to "normal" rainfall/runoff

Then later a sudden release of frozen water by volcanic heating, or?

All surface water now frozen into polar ice caps (fig. 14.2, pg. 236)

Possibility for life in the past (maybe now?)

Mars has been the origin of some of earth's most fearsome alien creatures

Invaders From Mars, War of the Worlds, My Favorite Martian

None identified by any of the Martian probes

Intense UV from sun would make "life as we know it" unlikely

However, "water is life" and Mars has water

Stay tuned for an update


The Outer (Jovian) Planets

General features of Jupiter and Saturn

Largest planets in our solar system

Jupiter is almost a binary partner to the sun

Each has a system of orbiting satellites (moons) and rings

Can be quite extensive

Saturn has an impressive ring structure and 19 moons

Basically mini-suns - Composed of hydrogen and helium

Theoretical internal structure - fig. 16.3, pg. 277

Pressure at depth compresses the hydrogen into liquid, then "metallic" form

With a small "ice and rock" core

Central cores may represent the original rock/ice bodies which accumulated from the nebula

With the hydrogen being "captured" at a later time

Not "rock" as we recognize it due to extreme pressure and temperature

Some form of iron, silica, and oxygen

The "ice" is also probably different from what goes into a glass of Pepsi

Any combination of hydrogen with carbon, nitrogen, or oxygen

Both radiate impressive amounts of heat from 2 sources

Residual heat from the initial condensation of the nebula

Newly generated heat from continued contraction of the gas

Well developed "atmospheres"

Hydrogen and helium, with methane (CH4) and ammonia (NH3)



In orbit: 16 moons, faint ring

Has an extensive cloud cover

Vivid colors (white, orange, red, brown)

Essentially condensed ammonia (anyone for a walk in the rain?)

Great Red Spot (fig. 16.2, pg. 276) and (fig. 16.12, pg. 284)

A large "storm" in the atmosphere - almost 30,000 km across!

Has been "stable" for at least 300 years

How can it last for so long?

Nothing solid to interfere with the circulation of the gas



In orbit: 19 moons. extensive rings



In orbit: 15 moons, intricate system of dark rings



In orbit: 8 moons, faint rings

Great Dark Spot: similar to GRS on Jupiter

Atmospheric storm 10,000 km across



Discovered after a systematic search

Its presence was indicated by "wobbles" in Neptune's orbit

In orbit: a single large moon (Charon)

Essentially a binary system