The Solar System : Planets
http://www.cs.wright.edu/~tkprasad
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SOLAR SYSTEM
• The Sun
• 8 Planets
• 3+ Dwarf Planets
• Over 150 moons /
satellites of the planets
• Comets, meteors, asteroids,
and interplanetary dust/space
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Simplified Evolution of Solar System
• In the beginning, our Solar System was a
huge disc of dirt, rocks, gas, ice, etc.
• In the middle of this disc, the Sun
formed itself and began to glow.
• In some distances from the centre, the
planets emerged from these rings of dirt,
rocks and gas.
Scale of Solar System : Distances
Scale of Solar System : Sizes
SUN : The Star
• Composition: 75% hydrogen and 25% helium by mass
• Age: The Sun’s age is about 5 billion years.
• Differential rotation duration
– At the equator the surface rotates once every 25.4 days
– while near the poles it rotates once every 36 days
• Core conditions
– Temperature is 15.6 million Kelvin
– Pressure is 250 billion atmospheres
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• Sun’s energy comes from
nuclear fusion (in which hydrogen
is converted to helium within sun’s core).
This energy is released as heat and light.
• Our sun is classified as a yellow main
sequence star.
– A star’s temperature determines its “color.” The
coldest stars are red. The hottest stars are blue.
– Surface temperature (Corona) : 60000 K
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Geocentric vs. Heliocentric Theory
• Geocentric Theory (or “Ptolemaic” Theory –
pronounced “Tole-ah-may-ic”) is an ancient
view of the universe based primarily on
religion, philosophy, and mathematical
ideals.
• Heliocentric Theory (or “Copernican”
Theory) is a revised view of the universe
based on the studies of Nicholas
Copernicus, who was a mathematician in
the 1500’s.
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PLANETS
A planet is a large, round
heavenly body that
orbits a star and shines
with light reflected from
the star.
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The Planets of the Solar System
• Planets are categorized according to
composition and size. There are two main
categories of planets:
– Small rocky planets (Mercury, Venus,
Earth, Mars, and Pluto)
– Gas giants (Jupiter, Saturn, Uranus, and
Neptune)
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PLANETS: Revised Definition
In the Solar System, a planet is a celestial body that:
• is in orbit around the Sun,
• has sufficient mass to assume
hydrostatic equilibrium (a nearly
round shape), and
• has "cleared the neighbourhood"
around its orbit.
A non-satellite body fulfilling only the first two of
these criteria is classified as a "dwarf planet".
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Revised Planets of the Solar System
• 8 Planets
– Small rocky planets (Mercury, Venus,
Earth, and Mars)
– Gas giants (Jupiter, Saturn, Uranus, and
Neptune)
• 5 Dwarf Planets
• Ceres, Pluto, Haumea, Makemake, and Eris.
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The Relative Size of the Planets in the Solar
System
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What are the nine planets?
HINT: My Very Educated Mother Just Showed Us Nine Planets
My Very Educated Mother Just Served Us Nachos
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
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MERCURY
• Closest planet to the sun
• About the size of Earth’s moon
• Takes 88 days to complete one revolution
around the sun
• No atmosphere
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MERCURY
• Orbit
– highly eccentric (oval)
– perihelion (closest point) is 46 million km
– aphelion (farthest point) is 70 million km
• Appears to travel fastest
• 8th largest in size
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VENUS
• 2nd planet from Sun
• 6th largest in size
• Brightest object in the early morning/evening
sky
– Also called “morning star” and “evening star”
• Very dry atmosphere
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VENUS
• Greenhouse Effect:
– Carbon dioxide in the atmosphere traps heat
causing the surface temperature to increase upto
9000 F.
• Inferior/Inner planet
– Shows phases when viewed from Earth
• Galileo observed phases
• Copernicus used data to develop heliocentric theory.
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EARTH: The Blue Planet
•
•
•
•
3rd planet from the Sun
period of rotation: 24 hours
period of revolution: 365.25 days
It is called the blue planet because of water
– Earth’s surface is composed of 71% water
– Oceans help maintain Earth’s stable temperatures.
• Only planet with known life
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• Earth has a distinct atmosphere.
– It screens Earth’s surface from harmful
radiation from the sun.
– It prevents meteorites from reaching
Earth’s surface.
– It traps heat to help maintain Earth’s
stable temperatures.
– Scattering of light by the atmosphere
makes the sky look blue in the day time
and red at sunset/sunrise.
• Otherwise, sky would have looked dark even
in day time.
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EARTH’s Moon
• Earth has one moon, about 1/6 mass of earth.
• It takes the same amount of time for the
moon to rotate once on its axis as it does for
it to orbit the earth (27.3 days).
– Thus, the same side of the moon always faces us.
• The moon’s surface is covered in dust and
rocky debris from meteor impacts.
– It has no water or atmosphere.
– The dark areas of the moon are large craters
called maria (Latin: “seas”).
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• The moon reflects light from the sun
onto the earth’s surface. Sometimes
the moon may appear reddish-brown in
color as the sunlight is deflected
through dust in the earth’s atmosphere.
• The moon’s gravitational effects on the
earth are most apparent in the
“coming” and “going” of the tides .
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EARTH
• Age: At least 4 1/2 billion years
• Mass: 6,600,000,000,000,000,000,000
(6.6 sextillion) tons (6.0 sextillion metric
tons).
• Surface features: Highest land—Mount
Everest, 29,035 feet (8,850 meters)
above sea level. Lowest land—shore of
Dead Sea, about 1,310 feet (399 meters)
below sea.
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• Temperature: Highest, 134 °F (56.7 °C) at
Greenland Ranch in Death Valley, CA on
July 10, 1913. Lowest, -128.6 °F (-89.6 °C)
at Vostok Station in Antarctica. Average
surface temperature, 59 °F (15 °C).
• Chemical makeup of the earth's crust (in
percent of the crust's weight): oxygen
46.6, silicon 27.7, aluminum 8.1, iron 5.0,
calcium 3.6, sodium 2.8, potassium 2.6,
magnesium 2.0, and other elements
totaling 1.6.
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Size Comparison: Radius
• Radius of Sun ~ 440,000 miles
• Radius of Earth ~ 4000 miles
• Radius of Moon ~ 1080 miles
• Radius of Sun is 110 times the radius of Earth
(10 times the radius of Jupiter), and radius of
Earth is 4 times the radius of Moon.
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MARS: The Red planet
• Mars is the 4th Planet from the Sun
• Solid carbon dioxide is found at the poles
• Mars is known as the Red Planet because its
soil is red colored
• Mons Olympus –
largest volcano
• Moons:
Phobos and Deimos
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Asteroid Belt : Between Mars and Jupiter
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JUPITER
• 5th planet from the sun
• Largest planet in the solar system
– Jupiter contains over 70% of the mass in the solar
system outside the Sun.
• It is about 11 times the radius and 330
times the mass of the earth.
– One-tenth the radius of the sun
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Giant red spot
• 2nd brightest planet in the sky
• It is the first representative of the outer
solar system.
• Unlike the inner planets, Jupiter is not a
solid body, but instead is a ball of gas and
liquid (mostly hydrogen and helium).
• Galeilian Moons: Io, Europa, Callisto,
Ganymede
Io
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Europa
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SATURN
• Sixth planet from the sun.
• Saturn is a gas giant with strong surface
winds (500 m/sec).
• Saturn is less dense than water.
• Saturn’s magnetic field is 20x less than
Jupiter's, but its core rotation period
(10.5 hours) is similar.
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SATURN’s Moons
• Titan is larger than planet Mercury!
• Mimas has a huge crater.
• Epimetheus and Janus, just inside the
orbit of Mimas, are continually
exchanging orbits with one another in
a "waltz" -- they are called the
co-orbital satellites.
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URANUS
• Seventh planet from the sun
• Most distant planet you can see without using
a telescope
• Has faint rings
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NEPTUNE
• Eighth planet from the sun
• The blue coloration of Neptune is probably
due to the presence of methane
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Discovery of Uranus and Neptune
• Sir William Herschel in England discovered
Uranus on March 13, 1781.
• Irregularities in the predicted orbit of Uranus led
astronomers Urbain Le Verrier in Paris and John
Couch Adams in Cambridge to separately begin
calculations to determine the nature and position
of a new planet. Eventually, Neptune was
discovered on September 23, 1846 by Berlin
Observatory.
– It was a sensational moment for 19th century science
and dramatic confirmation of Newton’s gravitational
theory.
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PLUTO : Dwarf planet
• Formerly, ninth planet from the sun
– Pluto used to be the farthest and the
smallest planet from the sun
– Rocky surface surrounded by frozen gases
• Pluto was located by 24-year old Clyde
Tombaugh and named in 1930.
• The name Pluto was proposed by Venetia
Burney, a eleven-year-old schoolgirl in
Oxford, England, after the name for the god
of the underworld.
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• Pluto has only one moon, Charon,
and was discovered only in 1978.
• Charon is half the size of Pluto itself,
which is unusually large for a moon.
– Because they are so close in size,
sometimes Pluto and Charon are
considered to be double-planet.
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Planets and Greek Mythology
• Mercury (Hermes) is the god of commerce, travel
and thievery in Roman mythology.
– The planet probably received this name because it
moves so quickly across the sky.
• Venus (Aphrodite) is the Roman goddess of love and
beauty.
– The planet is aptly named since it makes a beautiful
sight in the sky, with only the Sun and the Moon being
brighter.
• Earth (Gaia) is the only planet whose English name
does not derive from Greek/Roman mythology.
– The name derives from Old English and Germanic.
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Planets and Greek Mythology
• Mars (Ares) is the Roman god of War.
The planet probably got this name due
to its red color.
• Jupiter (Zeus) was the King of the Gods
in Roman mythology, making the name
a good choice for the largest planet in
our solar system.
• Saturn (Cronus) is the Roman god of
agriculture.
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Planets and Greek Mythology
• Uranus is the ancient Roman deity of the
Heavens, the earliest supreme god.
• Neptune (Poseidon), was the Roman god of
the Sea. Given the beautiful blue color of this
planet, the name is an excellent choice!
• Pluto (Hades) is the Roman god of the
underworld in Roman mythology. Perhaps the
planet received this name because it's so far
from the Sun that it is in perpetual darkness.
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Planet Temperatures
• All planets revolve around the
sun and are all at different
distances from the sun.
• The farther the planet is
away from the sun, the
colder it will be.
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Planet
Temp. (C)
Mercury
150
Venus
450
Earth
0
Mars
-50
Jupiter
-150
Saturn
-190
Uranus
-210
Neptune
-230
Pluto
-250
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Planet’s Distance
from the Sun
Distance from the Sun (millions)
4000
3674.5
3500
2794.4
3000
2500
1,784
2000
1500
886.7
1000
500
483.6
36
67.2
93
141.6
Mercury
Venus
Earth
Mars
0
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Saturn
Uranus
Neptune
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Number of Moons for Each Planet
Each planet has a different number of moons.
Planet
Moons
Mercury, Venus
Earth
0
1
Mars
Jupiter
Saturn
2
63
61
Uranus
Neptune
27
13
Pluto has 3 moons.
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Two ways of Discovering
Planets of other stars
• Observe a slight “wobble” of the star due
to gravitational effects of the planet.
• Observe variation in the brightness of
star due to eclipse as the planet passes
between us and the star (or in total light
received as star eclipses the planet).
Wobble Amplified:
Motion of two revolving bodies under mutual gravity
If the mass of the star
is much higher than
the mass of the planet,
then the distance of
the center of the mass
is much closer to the star
than to the planet.
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Wobble Amplified:
Motion of two revolving bodies under mutual gravity
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Telltale Tug of a Planet
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Star eclipsing planet, reducing total light
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Planet eclipsing star, reducing total light
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Examples
• http://antwrp.gsfc.nasa.gov/apod/ap050510.html
– First image of a extra-solar planet.
• http://antwrp.gsfc.nasa.gov/apod/ap000807.html
– The planet was discovered by the gravitational wobble it
created on its parent star, Epsilon Eridani.
• http://apod.nasa.gov/apod/ap090923.html
– CoRoT-7b was discovered by noting a predictable slight
decrease in the brightness of its parent star
• http://antwrp.gsfc.nasa.gov/apod/ap991115.html
– Combination of wobble and partial eclipse.
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Beyond Planets: Kuiper Belt
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Kuiper belt (30-100 AU)
contains 100,000 comets
Oort cloud extends out
to about 50,000 AU
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Solar System Debris : Comets
Comet Halley (1986)
Short Period Comets
•50-200 year orbits
•Halley’s period : 76 year
Comet Hale-Bopp (1997)
Long Period Comets
•105 or 106 year orbits
•Orbits: random orientations
•Orbits close to ecliptic
and large ellipticities
•Originate in Kuiper Belt
•Originate in Oort Cloud
Comet Trajectory
Perseid Meteor Shower in August
• http://www.youtube.com/watch?v=6XTBrYWrey0
• http://www.youtube.com/watch?v=8XVjT1gnYLg
• http://www.youtube.com/watch?v=7lIhQNvLkaY
&NR=1
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Leonid Meteor Shower:
Debris from Comet Tempel Tuttle
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Leonid Meteor Shower in November
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Why Meteor Shower is best after Midnight ?
Midnight
Rotational
Velocity
Orbital
Velocity
Two Showers for Halley