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The Solar System : Planets

http://www.cs.wright.edu/~tkprasad

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SOLAR SYSTEM

• The Sun

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• 3+ Dwarf Planets

• Over 150 moons / satellites of the planets• Comets, meteors, asteroids, and interplanetary dust/space

• 8 Planets

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

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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 KPrasad

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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

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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

MercuryVenusEarthMars

JupiterSaturnUranus

NeptunePluto

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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 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”).

EARTH’s Moon

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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 DeimosPrasad U3_SolarSystem

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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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• 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

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Io

Europa

Giant red spot

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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.

Planet Temp. (C)Mercury 150Venus 450Earth 0Mars -50

Jupiter -150Saturn -190Uranus -210

Neptune -230Pluto -250

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Planet’s Distance from the Sun

Distance from the Sun (millions)

36 67.2 93 141.6483.6

886.7

1,784

2794.4

3674.5

0

500

1000

1500

2000

2500

3000

3500

4000

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

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Number of Moons for Each PlanetEach planet has a different number of moons.

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Planet Moons

Mercury, Venus 0Earth 1Mars 2

Jupiter 63Saturn 61Uranus 27

Neptune 13

Pluto has 3 moons.

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

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If the mass of the staris much higher thanthe mass of the planet,then the distance ofthe center of the massis much closer to the starthan to the planet.

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

Solar System Debris : Comets

Comet Halley (1986) Comet Hale-Bopp (1997)

Short Period Comets Long Period Comets

•50-200 year orbits

• Halley’s period : 76 year

•Orbits close to ecliptic

•Originate in Kuiper Belt

•105 or 106 year orbits

•Orbits: random orientations

and large ellipticities

•Originate in Oort Cloud

Comet Trajectory

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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 ?

Rotational Velocity

Orbital Velocity

Midnight

Two Showers for Halley