The Planets & the Solar System

Chapter 27

The Solar System Ch. 27 Sec 1

• What are the 2 “planetary neighborhoods”?– inner planets– outer planets

• What separates these 2 “neighborhoods?”– asteroid belt

• What are the inner planets?– 4 closest to sun

• Mercury• Venus• Earth• Mars

– What is another name for the inner planets?

• “terrestrial” planets– b/c earthlike characteristics

» rocky crusts» dense mantle layers» very dense cores

Distance Between Planets Visualization

The Solar System

• What are asteroids?– solid, rocklike

masses that orbit the sun in same direction as planets

• Where are asteroids located?– between Mars &

Jupiter in asteroid belt that separates inner planets from outer planets

The Solar System

• What are the outer planets?– remaining 4 planets

• Jupiter• Saturn• Uranus• Neptune

• What is another name for the outer planets?– “Jovian” planets or Gas Giants

• How do they compare to the terrestrial planets?– considerably larger than Earth– gaseous

– less dense– have ring systems

The Solar System

• What about Pluto???– oddity of the solar system

• Not dense enough to be considered “terrestrial”.• Too small to be “Jovian”.

The Solar System

Inner Planets: Fun Facts• Mercury

– surface = many craters & smooth plains• formed by lava flowing from cracks in surface

– extremely hot day temps (400+°C) & extremely cold night temps (-200°C)

– no atmosphere b/c weak gravity

• Venus– “Earth’s twin/ sister planet”

• similar diameter, mass, & gravity

– Unlike other planets rotates from east to west (clockwise)

– day (243 Earth days) is longer than year (225 Earth days)

– atmosphere = mostly carbon dioxide (CO2)

• “runaway” greenhouse effect (~475°C)

– yellow clouds = sulfuric acid

Inner Planets: Fun Facts

• Mars (4th from sun)– 1st planet outside Earth’s orbit– period of rotation 1 day = ~24 ½ hrs – period of revolution (orbit) 1 yr = 687 Earth days

• …~2x as long as Earth’s year

– Axis tilted at almost same angle & in same direction as Earth’s

• similar 4 seasons but ~2x as long

– largest volcano in the solar system Olympus Mons– Valles Marineris canyon system (as long as the

United States is wide)

Inner Planets: Fun Facts

• Jupiter (5th from sun)– Largest planet

• More than 2x mass of all other planets combined

– Colored zones & belts– “Great Red Spot”

• May be calm area that rotates slowly in turbulent atmosphere

Outer Planets: Fun Facts Ch. 27 Sec. 2

• Saturn (6th from sun)– lowest density (0.7 g/cm3)

• less dense than water (1g/cm3)

– would float

– most visible ring system• believed to be chunks of ice

– colored zones & belts• rising & sinking gases• fewer than Jupiter

Outer Planets: Fun Facts

• Uranus (7th from sun)– inclination (tilt) of axis almost 90°

• So… rotates on its side• May have been tipped by collision

with Earth-sized mass early in history of the solar system

– Methane gives it its blue tint

Outer Planets: Fun Facts

• Neptune (8th from sun)– most distant Jovian planet

• occasionally outside Pluto’s orbit– b/c Pluto’s orbit sometimes brings

Pluto closer to the sun than Neptune

– Astronomers predicted existence mathematically

• in 1846

Outer Planets: Fun Facts

• Pluto (9th from sun)– occasionally 8th “planet” b/c

orbit sometimes brings it closer to Sun than Neptune

– Smallest “planet”• Smaller than 7 moons in our solar

system (including our moon)– Pluto & Charon (one of its moons)

are similar in mass» some scientists consider them to be a

“double planet” rather than a planet-moon system

Outer Planets: Fun Facts

• Pluto (continued)– New Horizons probe to Pluto launched Jan. 2006

• will fly by Pluto and Charon– Will take advantage of Jupiter's gravity (planned 2007 flyby)

which will boost the probe's velocity by 9,000 mph & get it to Pluto by 2015

– CBS Video of Pluto Probe

– No longer considered a “true” planet• Now considered one of over 40 “dwarf” planets

– Article on Why Pluto is No Longer Considered a Planet

Outer Planets: Fun Facts

Planetary Satellites Ch. 27 Sec. 3

• What is a satellite?– an object that orbits a planet– Example of natural satellites?

• moons

– Example of artificial satellite?• TV satellite, GPS satellite, etc.

• Earth moon = only natural satellite

• Mars 2 tiny irregularly shaped moons– Phobos– Deimos

• Jupiter at least 63 moons– 4 largest

• Galilean satellites (in honor of discoverer Galileo)– Io– Europa– Ganymede– Callisto

Planetary Satellites

• Saturn at least 61 moons– Titan

• only moon known to have substantial atmosphere

• Uranus at least 27 moons– 5 major moons

• Titania• Oberon• Umbriel• Ariel• Miranda

• Neptune at least 13 moons– Triton

Planetary Satellites

• What are comets?– “dirty snowballs”

• dust particles trapped in mixture of frozen water, carbon dioxide, methane, & ammonia

• Where are comets usually found?– spend most of their time beyond

Neptune’s orbit• consist only of solid main body

(nucleus)

• What are Trans-Neptunian Objects (TNOs)?– orbit beyond Neptune in Kuiper Belt

& Oort Cloud

Solar System Debris Ch. 27 Sec. 4

• comets (continued)– A few comets have highly

elliptical orbits that take them closer to the sun

• can become visible at night• Energy from the sun heats the

comet’s icy surface– Forms a coma (cloud of gas & dust that

expands into space)– solar wind pushes coma into space forming

tail pointing away from the sun

– Halley’s Comet (after astronomer Edmund Halley who noticed & predicted pattern of return)

• 76 years

Solar System Debris

• What are asteroids?– solid, rocklike masses probably left over from

formation of solar system

• How do asteroids orbit?– around sun in same direction as planets

• most have nearly circular orbits within asteroid belt between Mars & Jupiter

Solar System Debris

• What are meteors, meteoroids, & meteorites?– rocky or icy fragments;

smaller than asteroids• meteoroid traveling in

space• meteor passing through

Earth’s atmosphere– “shooting star”

• meteorites hit Earth’s surface

– What are the 3 basic types?» stony

» iron

» stony-iron

Solar System Debris

• What are impact craters?– bowl-shaped

depressions that remain after meteor or other object hits Earth, other planet, moon

• one of best known = Arizona’s Barringer Meteor Crater

Solar System Debris