Chapter 7 Our Planetary System What Does the Solar System Look Like? What Can We Learn by Comparing the Planets to One Another?

Chapter 7 7.1 Studying the Solar System Our Planetary System • Our goals for learning • What does the solar system look like? • What can we learn by comparing the planets to one another? • What are the major features of the Sun and planets?

Earth, as viewed by the Voyager spacecraft

What does the solar system look • Eight major like? planets with nearly circular orbits

• Pluto is smaller than the major planets and has a more elliptical orbit

What can we learn by comparing the planets to one another? • Planets all orbit in same direction and nearly in same plane

1 Comparative Planetology • Comparing the planets reveals patterns among • We can learn more about a world like our them Earth by studying in context with other worlds in the solar system. • Those patterns • Stay focused on processes common to provide insights multiple worlds instead of individual facts that help us specific to a particular world. understand our own planet

What are the major features of Planets are very tiny the Sun and planets? compared to distances between them.

Sun and planets to scale

Sun Mercury

• Over 99.9% of solar system’s mass • Made of metal and rock; large iron core • Made mostly of H/He gas (plasma) • Desolate, cratered; long, tall, steep cliffs • Converts 4 million tons of mass into energy each second • Very hot and very cold: 425°C (day), –170°C (night)

2 Venus Earth

Earth and Moon to scale • Nearly identical in size to Earth; surface hidden by clouds • Hellish conditions due to an extreme greenhouse effect: • An oasis of life • Even hotter than Mercury: 470°C, day and night • The only surface liquid water in the solar system • A surprisingly large moon

Jupiter Mars

• Much farther from Sun than inner planets • Mostly H/He; no solid surface • 300 times more massive than • Looks almost Earth-like, but don’t go without a spacesuit! Earth • Giant volcanoes, a huge canyon, polar caps, more… • Water flowed in the distant past; could there have been • Many moons, life? rings …

Saturn Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons

• Io (shown here): Active volcanoes all over • Giant and gaseous like Jupiter • Europa: Possible subsurface ocean • Spectacular rings • Ganymede: Largest moon in solar system • Many moons, including cloudy Titan • Callisto: A large, cratered “ice ball” • Cassini spacecraft currently studying it

3 Rings are NOT solid; Cassini probe they are made arrived July of countless 2004 small chunks of ice and (Launched in rock, each 1997) orbiting like a tiny moon.

Artist’s conception

Uranus Neptune • Smaller than Jupiter/Saturn; • Similar to Uranus much larger than (except for axis Earth tilt) • Made of H/He gas & hydrogen • Many moons compounds (including Triton) (H2O, NH3, CH4) • Extreme axis tilt • Moons & rings

Pluto

• Much smaller than other planets • Icy, comet-like composition • Its moon Charon is similar in size

4 What have we learned? What have we learned?

• What does the solar system look like? • What are the major features of the Sun and planets? – Planets orbit Sun in the same direction and in – Sun: Over 99.9% of the mass nearly the same plane. – Mercury: A hot rock • What can we learn by comparing the planets to – Venus: Same size as Earth but much hotter one another? – Earth: Only planet with liquid water on surface – Mars: Could have had liquid water in past – Comparative planetology looks for patterns – Jupiter: A gaseous giant among the planets. – Saturn: Gaseous with spectacular rings – Those patterns give us insight into the general – Uranus: A gas giant with a highly tilted axis processes that govern planets – Neptune: Similar to Uranus but with normal axis – Studying other worlds in this way tells us – Pluto: An icy “misfit” more like a comet than a planet about our own Earth

What features of the solar system 7.2 Patterns in the Solar System provide clues to how it formed?

• Our goals for learning • What features of the solar system provide clues to how it formed?

Motion of Large Bodies Two Main Planet Types

• All large bodies • Terrestrial in the solar planets are system orbit in rocky, relatively the same small, and close direction and in to the Sun nearly the same • Jovian planets plane are gaseous, • Most also rotate larger, and in that direction farther from Sun

5 Swarms of Smaller Bodies Notable Exceptions

• Many rocky • Several asteroids and exceptions to icy comets the normal populate the patterns need to solar system be explained

Special Topic: How did we learn the scale of the Transit of Venus solar system? • Apparent position of Venus on Sun during transit depends on distances in solar system and your position on Earth

Transit of Venus: June 8, 2004

What have we learned? Measuring Distance to Venus • What features of the solar system provide clues • Measure apparent to how it formed? position of Venus – Motions of large bodies: All in same on Sun from two direction and plane locations on Earth – Two main planet types: Terrestrial and jovian • Use trigonometry – Swarms of small bodies: Asteroids and to determine comets Venus’ distance – Notable exceptions: Rotation of Uranus, from the distance Earth’s large moon, etc. between the two locations on Earth

6 7.3 Spacecraft Exploration of the Solar How do robotic spacecraft work? System • Our goals for learning • How do robotic spacecraft work?

Flybys Orbiters

• A flyby mission • Go into orbit around another world flies by a planet • More time to gather data but cannot obtain just once detailed information about world’s surface • Cheaper than other mission but have less time to gather data

Probes or Landers Sample Return Missions

• Land on surface of another world • Gather samples • Spacecraft designed to blast off other world and return to Earth • Land on surface of another world • Apollo missions to Moon are only sample • Explore surface in detail return missions to date

7 What have we learned? Combination Spacecraft • How do robotic spacecraft work? – Flyby: Flies by another world only once. – Orbiter: Goes into orbit around another world – Probe/Lander: Lands on surface – Sample Return Mission: Returns a sample of another world’s surface to Earth

• Cassini/Huygens mission contains both an orbiter (Cassini) and a lander (Huygens)

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