Our Solar System IOur Solar System I

Origins of the Solar System

Astronomy 12

Learning Outcomes (Students will…)

-Explain the theories for the origin of the solar system

-Distinguish between questions that can be answered by science and those

that cannot, and between problems that can be solved by technology and those that cannot with regards to solar system formation.

-Estimate quantities of distances in parsec. Estimate the age of the solar system.

-Describe and apply classification systems and nomenclature used in the sciences. Classify planets as terrestrial vs. Jovian, inner vs. outer, etc.

Classify satellites. Classify meteoroid, asteroid, dwarf planet, planet. Classify comets as long period vs. short period. etc

-Formulate operational definitions of major variables. Given data such as diameter and density describe the properties that divide the planets and

moons into groups.

-Tools and methods used to observe and measure the inner and the outer

planets and the minor members of the solar system

Our Solar SystemOur Solar System

Our solar system is made Our solar system is made

up of:up of:

�� SunSun

�� Eight planets Eight planets

�� Their moonsTheir moons

�� Asteroids & Asteroids & MeteroidsMeteroids

�� CometsComets

Inner PlanetsInner Planets

The inner four rocky planets The inner four rocky planets

at the center of the solar at the center of the solar

system are:system are:

��MercuryMercury

��VenusVenus

��EarthEarth

��MarsMars

MercuryMercury

�� Planet nearest the sunPlanet nearest the sun

�� Second smallest planetSecond smallest planet

�� Covered with cratersCovered with craters

�� Has no moons or ringsHas no moons or rings

�� About size of EarthAbout size of Earth’’s moons moon

VenusVenus

�� Sister planet to EarthSister planet to Earth

�� Has no moons or ringsHas no moons or rings

�� Hot, thick atmosphereHot, thick atmosphere

�� Brightest object in sky besides sun and Brightest object in sky besides sun and

moon (looks like bright star)moon (looks like bright star)

�� Covered with craters, volcanoes, and Covered with craters, volcanoes, and

mountainsmountains

EarthEarth

�� Third planet from sunThird planet from sun

�� Only planet known to have life and Only planet known to have life and

liquid waterliquid water

�� Atmosphere composed of Nitrogen Atmosphere composed of Nitrogen

(78%), Oxygen (21%), and other gases (78%), Oxygen (21%), and other gases

(1%).(1%).

MarsMars

�� Fourth planet from sunFourth planet from sun

�� Appears as bright reddish color in the Appears as bright reddish color in the

night skynight sky

�� Surface features volcanoes and huge Surface features volcanoes and huge

dust stormsdust storms

�� Has 2 moons: Has 2 moons: PhobosPhobos and and DeimosDeimos

Asteroid BeltAsteroid Belt

�� Separates the inner, terrestrial planets Separates the inner, terrestrial planets

from the outer, Jovian planetsfrom the outer, Jovian planets

�� Contains ~100,000 asteroids.Contains ~100,000 asteroids.

�� Largest known asteroid: 4 Largest known asteroid: 4 VestaVesta

�� Largest object : Ceres (dwarf planet)Largest object : Ceres (dwarf planet)

Outer PlanetsOuter Planets

The outer planets composed The outer planets composed

of gas are :of gas are :

��JupiterJupiter

��SaturnSaturn

��UranusUranus

��NeptuneNeptune

JupiterJupiter

�� Largest planet in solar systemLargest planet in solar system

�� Brightest planet in skyBrightest planet in sky

�� At last count, 65 moons: 5 visible from At last count, 65 moons: 5 visible from EarthEarth

�� Strong magnetic fieldStrong magnetic field

�� Giant red spotGiant red spot

�� Rings have 3 parts: Halo Ring, Main Rings have 3 parts: Halo Ring, Main Ring, Gossamer RingRing, Gossamer Ring

SaturnSaturn

�� 66thth planet from sunplanet from sun

�� Beautiful set of rings Beautiful set of rings

�� 62 moons62 moons

�� Largest moon, Titan, Largest moon, Titan,

�� Easily visible in the night Easily visible in the night skysky

�� Voyager explored Saturn Voyager explored Saturn and its rings.and its rings.

UranusUranus

�� 77thth planet from sunplanet from sun

�� Has a faint ring systemHas a faint ring system

�� 27 known moons27 known moons

�� Covered with cloudsCovered with clouds

�� Uranus sits on its side with the north Uranus sits on its side with the north and south poles sticking out the and south poles sticking out the sides.sides.

NeptuneNeptune

�� 88thth planet from sunplanet from sun

�� Discovered through mathDiscovered through math

�� 12 known moons12 known moons

�� Triton largest moonTriton largest moon

�� Great Dark Spot thought to be a Great Dark Spot thought to be a

hole, similar to the hole in the hole, similar to the hole in the

ozone layer on Earthozone layer on Earth

A Dwarf PlanetA Dwarf Planet

�� Pluto is a small solid icy Pluto is a small solid icy

planet is smaller than the planet is smaller than the

Earth's Moon.Earth's Moon.

PlutoPluto

�� Never visited by Never visited by spacecraftspacecraft

�� Orbits very slowlyOrbits very slowly

�� CharonCharon, its moon, is , its moon, is very close to Pluto very close to Pluto and about the same and about the same sizesize

Two Types of Planets: Terrestrial and Jovian

Why?

• Sun, a star, at the center

• Inner (rocky) Planets

(Mercury, Venus, Earth, Mars) ~ 1 AU

• Asteroid Belt ~ 3 AU

• Outer (gaseous) Planets (Jupiter, Saturn, Neptune,

Uranus) ~ 5-40 AU

• Kuiper Belt ~ 30 to 50 AU

-includes Pluto

• Oort Cloud ~ 50,000 AU

What does the solar system look like from far away?

Bode’s Law•A rough rule that predicts the spacing of the planets in the Solar System

•To find the mean distances of the planets, beginning with the following simple sequence of numbers:

0 3 6 12 24 48 96 192 384

•With the exception of the first two, the others are simple twice the value of the preceding number.

•Add 4 to each number:4 7 10 16 28 52 100 196 388

•Then divide by 10:0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 38.8

PlanetPlanet Actual Distance (AU)Actual Distance (AU) BodeBode’’ss LawLaw

Mercury 0.39 0.4

Venus 0.72 0.7

Earth 1.00 1.0

Mars 1.52 1.6

Jupiter 5.20 5.2

Saturn 9.54 10.0

Uranus 19.2 19.6

Neptune 30.1 38.8

Works for

moons too!

AsteroidsAsteroids

�� Small bodies Small bodies

�� Believed to be left over Believed to be left over from the beginning of from the beginning of the solar system the solar system billions of years agobillions of years ago

�� 100,000 asteroids lie in 100,000 asteroids lie in belt between Mars and belt between Mars and JupiterJupiter

�� Largest asteroids have Largest asteroids have been given namesbeen given names

Most asteroids are

located in two regions:

•Asteroid belt

•Orbit of Jupiter… the Hildas (the orange

"triangle" just inside the orbit of Jupiter) and the

Jovian Trojans (green). The group that leads

Jupiter are called the "Greeks" and the trailing

group are called the "Trojans"

Where are the asteroids?

CometsComets

�� Small icy bodiesSmall icy bodies

�� Travel past the SunTravel past the Sun

�� Give off gas and dust as Give off gas and dust as

they pass bythey pass by

Anatomy of a Comet

Where are the comets?

Kuiper BeltA large body of small

objects orbiting (the short

period comets <200 years) the Sun in a radial zone

extending outward from the

orbit of Neptune (30 AU) to about 100 AU. Pluto maybe

the biggest of the KuiperBelt object.

Oort CloudLong Period Comets

(period > 200 years) seems to come mostly from a

spherical region at about

50,000 AU from the Sun.

Key Ideas

� Properties of the Planets: All of the planets orbit the Sun in the same direction and in almost the same plane. Most of the planets have nearly circular orbits.

� The four inner planets are called terrestrial planets. They are relatively small (with diameters of 5000 to 13,000 km), have high average densities (4000 to 5500 kg/m3), and are composed primarily of rocky materials.

� The four giant outer planets are called Jovian planets. They have large diameters (50,000 to 143,000 km) and low average densities (700 to 1700 kg/m3) and are composed primarily of light elements such as hydrogen and helium.

Key Ideas

� Satellites and Small Bodies in the Solar System:Besides the planets, the solar system includes satellites of the planets, asteroids, comets, and trans-Neptunian objects.

� Seven large planetary satellites (one of which is our Moon) are comparable in size to the planet Mercury. The remaining satellites of the solar system are much smaller.

Key Ideas

� Asteroids are small, rocky objects, while comets and trans-Neptunian objects are made of ice and rock. All are remnants left over from the formation of the planets.

� Most asteroids are found in the asteroid belt between the orbits of Mars and Jupiter, and most trans-Neptunian objects lie in the Kuiper belt outside the orbit of Neptune. Pluto is one of the largest members of the Kuiper belt.

Key Ideas

� Spectroscopy and the Composition of the Planets:Spectroscopy, the study of spectra, provides information about the chemical composition of objects in the solar system.

� The spectrum of a planet or satellite with an atmosphere reveals the atmosphere’s composition. If there is no atmosphere, the spectrum indicates the composition of the surface.

� The substances that make up the planets can be classified as gases, ices, or rock, depending on the temperatures at which they solidify.

Key Ideas

� Impact Craters: When an asteroid, comet, or meteoroid collides with the surface of a terrestrial planet or satellite, the result is an impact crater.

� Geologic activity renews the surface and erases craters, so a terrestrial world with extensive cratering has an old surface and little or no geologic activity.

� Because geologic activity is powered by internal heat, and smaller worlds lose heat more rapidly, as a general rule smaller terrestrial worlds are more extensively cratered.

Key Ideas

� Magnetic Fields and Planetary Interiors: Planetary magnetic fields are produced by the motion of electrically conducting liquids inside the planet. This mechanism is called a dynamo. If a planet has no magnetic field, that is evidence that there is little such liquid material in the planet’s interior or that the liquid is not in a state of motion.

� The magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state. The stronger fields of the Jovian planets are generated by liquid metallic hydrogen or by water with ionized molecules dissolved in it.