Chapter 29. Early Ideas – Geocentric Model: “Earth-Centered” The Sun, planets, and stars...

The Solar System

Chapter 29

Overview of Our Solar System

• Early Ideas– Geocentric Model: “Earth-Centered” • The Sun, planets, and stars orbited a

stationary Earth.


• The normal motion for all planets, as observed from Earth, is toward the east. -> Occasionally, a planet will move in the

opposite direction across the sky

• Retrograde Motion: A planet’s backward motion in the sky

Retrograde Motion


• Nicolaus Copernicus suggested the sun was the center of the solar system.– Heliocentric Model: “Sun-Centered”

• The Earth and the other planets orbit the Sun.

• Explained retrograde motion…-> the inner planets move faster in their

orbits than the outer planets do. -> when Earth passes a slower moving outer

planet, it appears that the outer planet temporarily moves backward in the sky

Heliocentric Model


• Kepler’s First Law– Johannes Kepler demonstrated that each

planet orbits the Sun in a shape called an ellipse.

– An ellipse is an oval shape that is centered on two points called foci.


• The major axis is the line that runs through both foci; it’s the maximum diameter of the ellipse.

• Astronomical Unit (AU): The average distance between the Sun and the Earth - 1.496 x 10^8 km = 1 AU

• The average distances between the Sun and planets are measured in astronomical units


• Eccentricity: The shape of a planet’s orbit is defined by eccentricity, which is the ratio of the distance between the foci to the length of the major axis.– Eccentricity values range from 0 to 1

• 0 is a perfect circle; 1 is a very elongated oval (parabola)


• Perihelion: when a planet is closest to the Sun in its orbit.

• Aphelion: when a planet is furthest from the Sun in its orbit.


• Kepler’s Second Law– An imaginary line between the Sun and a

planet sweeps out equal amounts of area in equal amounts of time

• Kepler’s Third Law– Mathematical relationship between the size of

a planet’s ellipse and its orbital period. P^2 = a^3• The square of the orbital period (P) = the

cube of the semimajor axis of the orbital ellipse (a)• P is measured in Earth years and a is

measured in AU


• Galileo Galilei1. Became the first person to use a

telescope to observe the sky which supported Copernicus’s idea the planets orbit the Sun.

2. Discovered that four moons orbit the planet Jupiter.

- Proved that not all celestial bodies orbit Earth,therefore, Earth is not the center of the solar system.


• Isaac Newton– Law of Universal Gravitation:• Any two bodies attract each other with a

force that depends on their masses and the distance between the two bodies • F = G m1m2

r^2


• Isaac Newton– Center of Mass: Each planet orbits a

point between it and the Sun.• The center mass is the balance point

between two orbiting bodies• ie: if one of two bodies orbiting each other is

more massive than the other, the center of mass is closer to the more massive body.

Formation of Our Solar System

• Stars and clouds form from clouds of dust and gas called interstellar clouds– Consist mostly of gas, hydrogen & helium

• Density of interstellar gas is very low, however, it can condense as a result of gravity and become concentrated enough to form a star and possibly planets– Astronomers hypothesize this is how the

solar system formed.


Nebular Theory

• The solar system formed from a rotating cloud of dust and gas.

• The sun formed at the center of the rotating disk.

• Planetesimals collided, eventually gaining enough mass to be planets.


• Planetesimals are small, irregularly shaped bodies formed by colliding matter.

Nebular Theory


• Comets – Comets are small icy bodies made of

rocky and metallic pieces held together by frozen gases.

– Comets generally revolve about the sun in elongated orbits.


Features of a Comet: A. Coma

- A coma is the fuzzy, gaseous component of a comet’s head.

B. Nucleus- The small solid core- When the nucleus is heated, it releases gases and

dust particles that form the coma and tails

C. Tail - Tails are pushed away from the coma by particles

and ions coming from the sum, as well as by the pressure of radiation from the Sun

Comet’s Tail Points Away from the Sun


Two clusters of comets:1. Kuiper Belt The Kuiper Belt is made up of millionsof icy and rocky objects that orbit ourSun beyond the orbits of Neptune andPluto. (30-50 AU from the Sun)


2. Oort CloudThe Oort Cloud is a sphere of cometssurrounding the sun and planets

(100,000AU from the Sun)


• Occasionally, a comet is disturbed by the gravity of another object and is thrown into the inner solar system.

• Comets that repeatedly orbit into the inner solar system are known as periodic comets. – Comet Halley is a well-known short-

period comet with a 76 year period


• Meteor Showers:–When Earth intersects a cometary orbit,

we experience a meteor shower as particles from the comet burn up upon entering Earth’s atmosphere


Asteroids • Asteroids are small, rocky bodies that orbit the

sun- They are thought to be leftover planetesimal

pieces from the time of the solar system’s formation that never formed planets

• Most of them lie between the orbits of Mars and Jupiter. (Asteroid Belt) – On the inner edge of this main belt, asteroids

take about three years to orbit the Sun. – Those near the outer limit of the main belt take

twice as long.

Irregular Orbits of Asteroids


• MeteoroidsA. A meteoroid is a piece of interplanetary

material that falls toward Earth and enters its atmosphere.

B. A meteor is the luminous phenomenon observed when a meteoroid enters Earth’s atmosphere and burns up, popularly called a shooting star.

C. A meteorite is any portion of a meteoroid that does not completely burn up in Earth’s atmosphere and strikes Earth’s surface.


• Most meteoroids originate from any one of the following three sources:

(1)interplanetary debris that was not gravitationally swept up by the planets during the formation of the solar system,

(2) material from the asteroid belt, or

(3) the solid remains of comets that once traveled near Earth’s orbit.

The Sun

• Our sun accounts for 99.85% of the mass of the Solar System

The Planets

• The planets make up most of the other.15% of the solar system

Planet Classification • Terrestrial = “Earth Like”–Mercury, Venus, Earth and Mars• Dense, consisting mostly of rocky and

metallic substances and only minor amounts of gases and ices.

• Jovian = “Jupiter Like”– Jupiter, Saturn, Uranus, Neptune• Contain large amounts of gases

(hydrogen & helium) and ices (mostly water, ammonia, and methane).

Terrestrial Planets • Terrestrial planets are small and

rocky. *Mercury, Venus, Earth & Mars*

Jovian Planets

• Jovian planets are huge gas giants. *Jupiter, Saturn Uranus &

Neptune*

The Interiors of the Planets

• The substances that make up the interiors

• of planets are divided into three groups:

• gases, rocks, and ices.

The Atmosphere of the Planets

• A planet’s ability to retain an atmosphere depends on its mass and temperature, which accounts for the difference between Jovian and the Terrestrial planets.


• The Jovian planets have very thick atmospheres of hydrogen, helium, methane, &ammonia.


• The terrestrial planets, including Earth, have meager atmospheres at best.

The Terrestrial Planets• Mercury “The Swift Planet”

– The innermost planet and second smallest planet in the solar system (slightly larger than Earth’s moon).

– has no moons – Slow spin – 1,407.6 hours

• After one spin, Mercury has orbited the Sun 1 ½ times • In two of Mercury’s years, three of Mercury’s days have

passed

A. Atmosphere - Essentially no atmosphere- Daytime surface temperatures 427°C- Nighttime temperatures -173°C

The Terrestrial Planets

B. Surface Features - Cratered highlands and vast smooth

terrains that resemble maria on the moon. - Planetwide system of cliffs, called scarps

C. Interior- High density suggests an extensive iron-

nickel core - Magnetic field suggests that there is a

molten zone in its interior

Mercury

• Venus “The Veiled Planet” – Venus is similar to Earth in size, density, mass,

and location in the solar system.• referred to as “Earth’s twin.”

– No moons– Brightest planet in the sky because it is close

and its albedo is 0.75– Thick clouds – Slow spin

• One day on Venus is 246 Earth days

– Clockwise spin is opposite most planets • Retrograde rotation• Caused by collision between Venus & another body



A. Atmosphere- Average surface temp is extremely hot: hottest in

the solar system- 464°C hot enough to melt lead!

- Atmospheric pressure is 92 atm. would make you feel like you were in 915m of water

- Primarily carbon dioxide and nitrogen - Clouds are composed of sulfuric acid & are 35km

thick- Greenhouse gas (CO2) prevent infrared radiation

from escaping & keeps the surface hot• liquid water cant exist


B. Surface Features -About 80% of Venus’ surface consists of plains covered by lava flow.-Only a few compact craters- Relatively young, last volcanic activity occurred 500 million years ago- Little evidence of tectonic activity

C. Interior - Size and density is similar to Earth so most likely internal structure is similar (no seismic evidence to prove this )- Liquid metal core that extends halfway to the surface - No measurable magnetic field due to slow rotation rate

Venus


• Earth “The Blue Planet”- nearly circular orbit allow liquid water to

exist on its surface in all three states: solid, liquid, gas

- 1. Abundance of water, 2. moderately dense atmosphere & 3. mild greenhouse effect support conditions suitable for life


• Precession: The wobble in Earth’s rotational axis– Takes Earth’s rotational axis about

26,000 years to go through one cycle of precession

– The sideways pull that causes precession comes from the Moon and Sun’s gravitational force on Earth

• Mars “The Red Planet”

- Red because of its high iron content in the soil. - Smaller and less dense than Earth- Two irregularly shaped moons - Phobos &

Deimos (captured asteroids)

A. Atmosphere- The Martian atmosphere has only 1% of the

density of Earth’s.- Very thin atmosphere- Turbulent - Constant wind, dust storms



B. Surface Features - southern hemisphere is heavily cratered, highland region- Northern hemisphere is dominated by plains that are

sparsely cratered (lava flows covered N. hemi)- 4 large shield volcanoes: largest is Olympus Mons the

largest mountain in the solar system! 3x higher than Mt. Everest & the base would cover the

state of Colorado - Enormous canyon, Valles Marineris- Dried river and lake beds, outflow channels, & runoff

channels Erosional features that suggest liquid water once

existed - Polar ice caps covering both poles

Made of carbon dioxide ice a.k.a. “dry ice”


• C. Interior – Unsure of internal structure– Hypothesize core of iron and nickel and

possibly sulfur– No magnetic field, therefore probably a solid

core– Above core is a mantle– No evidence of current tectonic activity or

tectonic plates

Mars

The Jovian Planets

• I. Jupiter “The Giant Among Planets” – Jupiter has a mass that is 2 1/2 times greater

than the mass of all the other planets and moons combined.

A. Structure of Jupiter 1. Jupiter’s hydrogen-helium atmosphere also contains small amounts of methane, ammonia, water, and sulfur compounds.

B. Jupiter’s Moons 1. Jupiter’s satellite system, including the 67 moons discovered so far, resembles a miniature solar system.• Io – volcanically active• Europa – icy surface• Ganymede – largest Jovian moon, cratered• Callisto – densely cratered

The Jovian Planets

The Jovian Planets

C. Jupiter’s Rings 2. Jupiter’s ring system was one of the most unexpected discoveries made by Voyager 1.• Composed of fine, dark particles similar to smoke

particles

Jupiter

Jupiter’s Moons

The Jovian Planets

• II. Saturn “The Elegant Planet” – The most prominent feature of Saturn is its

system of rings.

A. Features of Saturn1. Saturn’s atmosphere is very active, with winds

roaring at up to 1500 kilometers per hour.2. Large cyclonic “storms” similar to Jupiter’s Great

Red Spot, although smaller, occur in Saturn’s atmosphere.

The Jovian Planets

B. Saturn’s Rings 1. Most rings fall into one of two categories based on particle density.• Each ring is composed of individual particles –

moonlets of ice and rock- that circle the planet while regularly impacting one another.

C. Saturn’s Moons 1. Saturn’s satellite system consists of 62 moons.2. Titan is the largest moon, and it is bigger than Mercury.

Saturn

Cassini Approaching Saturn

The Jovian Planets• III. Uranus “The Sideways Planet” – Instead of being generally perpendicular to the

plane of its orbit like the other planets, Uranus’s axis of rotation lies nearly parallel with the plane of its orbit.

A. Uranus’ Moons1. 27 moons2. Varied terrains of the 5 largest moons

• Miranda = innermost moon has a greater variety of landforms than any body examined in the solar system

Uranus

The Jovian Planets

• IV. Neptune “The Windy Planet”– Winds exceeding 1000 kilometers per hour

encircle Neptune, making it one of the windiest places in the solar system.

A. Neptune’s Rings1. Rings are incomplete (described as arcs)

The Jovian Planets

B. Neptune’s Moons 1. 13 known moons2. Largest moon, Triton, is nearly the size of Earth’s moon• Only moon in solar system that exhibits retrograde

motion • Lowest surface temperature measured on any body

in the solar system -200° C• Displays volcanic-like activity

Neptune

The Jovian Planets

• IV. Pluto “The Dwarf Planet” – Pluto’s orbit is highly eccentric, causing it to

occasionally travel inside the orbit of Neptune, where it resided from 1979 through February 1999.

A. Pluto’s Moons1. Charon is more than ½ the size of Pluto2. Orbits Pluto once every 6.4 days at a distance 20 times closer than Earth’s moon orbits Earth.

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Chapter 29. Early Ideas – Geocentric Model: “Earth-Centered” The Sun, planets, and stars...

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