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Earth / Environmental Science
Ch. 23 – Touring Our Solar System
THE SOLAR SYSTEM
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Every planet travels in the same direction, and moves in an elliptical
orbit
Mercury is the closest planet to the Sun
Pluto is the farthest planet from the Sun
The Planets: An Overview
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Terrestrial planets - relatively small and rocky (Mercury, Venus,
Earth, Mars)- also known as the inner planets
Jovian planets - huge gas giants (Jupiter, Saturn, Uranus, Neptune)also known as the outer planets (and Pluto)
Terrestrial and Jovian planets differ by size, density, chemical makeup
and rates of rotation.
The Interiors of the Planets
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Substances that make up the planets are divided into 3 groups:
1. The gases- hydrogen and helium- have melting points near
absolute zero
2. The rocks- mainly silicate minerals and metallic iron- melting
point above 700 degrees Celsius
3. The ices- include ammonia, methane, carbon dioxide and water
Terrestrial planets are dense and mostly rocky and metallic substances
Jovian planets contain large amounts of gases and ices
The Atmospheres of the Planets
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Jovian planets have thick atmospheres (hydrogen, helium, methane,
ammonia)
Terrestrial planets have little atmosphere
A planet’s ability to retain an atmosphere depends on it’s mass and
temperature
More massive terrestrial planets (Earth, Mars, Venus) hold heavy
gases
Jovian planets have greater surface gravities
Formation of the Solar System
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Nebula- a cloud of dust and gas in space
A nebula is made of 92% hydrogen, 7% helium, and less than 1% of
remaining heavier elements
The Nebular Theory states that the sun and planets formed from a
rotating disk of dust and gases
Planetesimals
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Planetesimals- small, irregularly shaped bodies
The growth of planets began as solid bits of matter collided and
clumped together through a process called accretion
THE TERRESTRIAL PLANETS
Mercury: The Innermost Planet
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Mercury is the innermost and second smallest planet (hardly larger
than Earth’s moon)
Has cratered highlands, smooth terrains, and deep slopes
One full rotation of Mercury takes 59 Earth-days, therefore, one night
on Mercury lasts about 3 months
Temperatures drop to about –173o Celsius at night and reach 427 o
Celsius during noontime
Mercury has the greatest temperature extremes of any other planet
Venus: The Veiled Planet
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Named for the goddess of love and beauty
Orbits around the sun every 255 Earth-days
Similar to Earth in size, density, mass and location in the solar system
Covered in thick clouds that cannot be penetrated by visible light
Venus’ surface is shaped by basaltic volcanism and tectonic activity
About 80% of the surface consists of plains covered by volcanic flows
and 8% consists of highlands that might be similar to the ones on
Earth
Tectonic activity may be driven by upwelling and downwelling of
materials in the planet’s interior
The temperature reaches 475 o Celsius and the atmosphere is 97%
carbon dioxide
Mars: The Red Planet
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Known as The Red Planet because it looks like a reddish ball when
seen through a telescope
The atmosphere has 1% the density of Earth’s, and many dust storms
occur even though it has a thin atmosphere
Has hurricane-force winds up to 270 km per hour that can go on for
weeks
There are many canyons that are much bigger than the Grand Canyon
There are many giant volcanoes, one is about the size of Ohio
The first spacecraft that orbited Mars found many large volcanoes,
about the size of Ohio
There was evidence of liquid water found on the planet
Temperatures range from –70 degrees Celsius to –100 degrees Celsius
THE JOVIAN PLANETS
The Outer Planets- Jupiter
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Jupiter’s mass is 2½ times greater than the mass of all of the other
planets and moons combined
Rotates more rapidly than any other planet
Atmosphere is made of hydrogen and helium (contains small amounts
of methane, ammonia, water and sulfur compounds)
The interior heat of Jupiter produces huge convection currents in the
atmosphere
Is thought to be a gigantic ocean of liquid hydrogen
Has 28 discovered moons
Galileo discovered the 4 largest moons
One of the moons, Io, is one of the three volcanically-active bodies in
our solar system
The planet’s rings are made of fine, dark particles
The rings are thought to be fragments dispersed by by meteorite
impacts from the surfaces of Metis and Adrastea, two small moons of
Jupiter.
Saturn
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Almost twice as far from the sun as Jupiter
The first rings found on Saturn were discovered by Galileo
Saturn has very strong winds and big cyclone storms
Saturn has seven rings that are all made of different individual
particles
The 2 main rings contain particles called “moonlets” that are very thin
and collide as they orbit the planet
Saturn’s satellite system contains 31 moons
Titan is the largest moon (second biggest in the solar system) and is
bigger than the planet Mercury
Uranus
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Uranus’ axis of rotation lies almost parallel of its orbit, instead of lying
perpendicular
Has 9 distinct ring belts
Has long, deep canyons and linear scars
Neptune
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Has very strong winds (over 1000 kilometers per hour)
Has a large, rotating storm called the Great Dark Spot
Contains cirrus-like clouds over the main cloud deck
Triton is the largest of Neptune’s 13 moons
Pluto
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About 40 times farther from the sun than Earth
It takes around 248 Earth-years to orbit the sun
Has a diameter of about 2300 kilometers, which makes it the smallest
planet
The average temperature is –210 degrees Celsius
MINOR MEMBERS OF THE SOLAR SYSTEM
Asteroids: Microplanets
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Asteroids are small rocky bodies that have been likened to “flying
mountains”
Most asteroids lie between the orbits of Mars and Jupiter
Some asteroids travel near the sun and some travel near the Earth
Many asteroids have irregular shapes
Comets
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Comets are pieces of rocky and metallic materials held together by
frozen gases(such as ammonia, water, methane, carbon dioxide and
carbon monoxide)
Travel in elongated orbits
Take hundreds of thousands of years to complete a single orbit around
the sun
Coma
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A coma is a fuzzy, gaseous component of a comet’s head
A small glowing nucleus can be detected in a coma
Radiation pressure and solar wind contribute to the formation of a
coma
As comets move away from the sun, the gases forming a coma
recondense
Kuiper Belt, Oort Cloud and Halley’s Comet
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Short orbital periods are thought to orbit in a region called the Kuiper
belt
Most Kuiper belt comets move in almost circular orbits
A spherical shell around the solar system is called an Oort cloud
Tiny portions of oort clouds pass into the inner solar system
The most famous short-period comet is Halley’s comet
Its orbital period is about 76 years
Halley’s comet developed a tail about 1.6 million kilometers long
Meteoroids
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A meteoroid is a small solid particle that travels through space
Most meteoroids from one of three sources:
Interplanetary debris that was not gravitationally swept up by the
planets during the formation of the solar system
Material from the asteroid belt
The solid remains of comets that once traveled near Earth’s orbit
The meteoroids that do not enter Earth’s atmosphere and burn up are
called meteors
Meteor sightings are also known as meteor showers
A meteoroid that actually reaches Earth’s surface is called a meteorite