Chapter 27 PLANETS OF THE SOLAR SYSTEM



Chapter 27 PLANETS OF THE SOLAR SYSTEM

Read pp 685-7 and 695-708.

27.1 Formation of the Solar System (key terms: p 685)

The Nebular Hypothesis (Laplace, French mathematician 1796)

The sun and planets condensed at about the same time out of a rotating cloud of gas and dust approx. 5 billion years ago. (Rotating cloud from which sun &planets formed is called the solar nebula.) Center became hotter and denser due to forces from collisions and gravity. When temp=107 oC, hydrogen fusion began &Sol (THE SUN) formed. The sun contains 99% of the mass of the former solar nebula. (Fig 1 shown Orian nebula-not yet a solar system.)

Formation of the Planets (Fig 2 shows steps.)

Small bodies from which planet forms=planetesimals. Clumping planetesimals for larger bodies called protoplanets. Clumping protoplanets and planetesimals eventually may become planets and moons.

Inner Planets (Mercury, Venus, Earth, Mars)

Contain large %’s of heavy elements (ex: iron, nickel). Inner planets lost their dense gases because at the temperature of the gases, gravity wasn’t strong enough to hold onto them; solar radiation may have blown or boiled away gases. As densest materials sank, layers formed. Inner planets are smaller, denser, rockier than outer planets.

Outer Planets (Jupiter, Saturn, Uranus, Neptune; NOT Pluto)

Colder B/C they are further from the sun, so they didn’t lose their gaseous atmospheres. (Gases include helium, hydrogen, water (ice), methane (ice), ammonia (ice). Outer planets are gas giants; Jupiter is 24%as dense as Earth, but has diameter 11x larger than Earth.

The Different Planet—Pluto (NOT considered a planet by the astronomy community)

Pluto is smaller than Earth’s moon. It is an ice ball made of frozen gases and rocks.

27.3 The Inner Planets

|Mercury: 1 |Venus: 2 |Earth: 3 |Mars: 4 |

|Closest to the Sun |Second from Sun |Third from Sun |Fourth from the Sun |

|Orbits in 88 days |Orbits in 225 days |Orbits in 365 ¼ days |(50% further from Sun than |

|Rotates 1x in 58 days |Rotates 1x in 234 days |Rotates 1x in 1 day |Earth) |

|Many craters/cliffs |Atmosphere=96%CO2! |Has one moon |Orbits in 687 days |

|No significant atmosphere |SO2 in upper atmosphere strongly|LIQUID water@ surface |Rotates 1x in 24h37min. |

|Day temp=427oC |reflects light; |Atmosphere is 80%N2, 16%O2. Also|Geologically active in past. |

|Night temp=-173oC |Commonly called the evening star|CO2, H2O. |Has mountains, BIG |

| |or morning star. |Supports life. Geology similar |volcanoes,erosion/canyons |

|P695/fig1 |Average temp=464 oC |to Venus; but plate tectonics |No significant atmosphere |

| |Surface has basalt and granite |prevent formation of huge |Temperatures range from 20oC nr |

| |rocks |volcanoes. |equator (summer) to -130oC nr |

| |Has mountains, BIG volcanoes, | |poles(winter) |

| |lava plains, sand dunes p696/fig|P698/fig 4 | |

| |2 | |P699/fig 5 |

27.4 The Outer Planets (Gas Giants; see fig 1) (Pluto is not a planet.) [ starts p 701]

Gases : ________________ and _________________

Core: _________________ and __________________

Rings=_______________________________________ from _____________________

Jupiter: 5

Largest planet in solar system (SS)

Orbits in 12 yrs

Rotates 1x in 9h50min

Has 60 moons, 4which are the size of planets

Has thin rings

Hydrogen, helium are 92%of atmosphere

Rocky iron core?

Not enough mass to become a star

Bands=organic molecules, methane, ammonia, water (g) patterns due to rotation.

Avg. temp=-160oC

HUGE storms (Great red spot=BIG hurricane)

Galileo probe:

winds>540 km/h

Jupiter’s internal heat affects weather more than solar heat.

P702/fig 2

Moons: Gannymede, Callisto, Europa, Io |Saturn: 6

Orbits in 29.5 yrs

Rotates in 10hr30min

Rings=2x Saturn’s dia

Rings made of ice /dust

fr comets&other bodies

60+moons, Titan=1/2dia of earth

Atmosphere similar to 5

Least dense planet in SS

Bands parallel to equator due to rotation

Equatorial bulge

NASA Cassini (7/1/04)

And ESA Huygens probes sent to study Saturn and its moons.

P 704/fig 4 |Uranus: 7

Orbits in 84 yrs

Rotates in 17 hr

3rd largest planet

at least 24 moons, 11 rings

Rotational axis is nearly parallel to orbital plane

(Voyager 2 discovery, 1986)

Atmosphere is mostly hydrogen, helium; blue-green=methane

Avg cloud t =-214oC; planet may be much hotter

(Core temp7000oC)

Hubble Space Telescope used to study Uranus

p705/fig 5 |Neptune: 8

Orbits in 164 yrs

Rotates in 16h

Similar to Uranus (size, mass)

At least 8 moons, 4 rings(?)

Discovered because it affected Uranus orbit (gravity)

Atmosphere is mostly hydrogen, helium, methane. (Bands)

Great dark spot=storm the size of Earth

(1000 km/h winds)

Avg cloud t=-225oC

P706/fig 6 | |

Pluto (discovered 1930): p707/fig 7

Orbits the Sun in elongated, tilted ellipse. Atmosphere=nitrogen. Surface=methane, rocks, ice.

Avg temp=-235 oC. Moon=Charon, half of Pluto’s size

Kuiper belt=region beyond Pluto containing small bodies (mostly ice). Quaoar=3/4ths Pluto’s size.

Beyond Kuiper belt: Sedna (discovered 3/04) 3x farther from Earth than Pluto.

Exoplanets= (p708/fig 8)Planets circling stars other than the Sun. Exo=______________________

Hard to observe. Detected due to gravity/Doppler shift of light from stars, larger than Uranus.

(Bill Arnett is a software engineer, but his sources include NASA/JPL)

There are moons larger than Pluto. Pluto isn’t considered to be a planet anymore. There are 2 moons larger than Mercury.

is a video comparison on youtube with animated models of Ptolomy’s Solar System model (geocentric) and Copernicus’ Solar System model (Heliocentric)

Inner planets are also called terrestrial planets because they are similar to Earth. (Solid rock with metallic cores. Moons vary from 0-2. Impact craters on surface.

Outer planets are also called Jovian planets (gas giants). Asteroid belt separates inner and outer planets.

is a Penn State video about rotation of gas giants.

Read pages 688-694

Formation of Solid Earth

Collisions of planetesimals, compression of inner layers and radioactivity led to Earth’s extremely high temperature during formation.

Early Solid Earth: Differentiation led to the most dense elements (including iron) sinking to the center to form a molten iron and nickel core. The thick mantle surrounds the core and contains iron and magnesium-rich rocks. The thin crust is less sense silica-rich rocks (ex: quartz, sand). Plate tectonics (shape the Earth) are driven by heat transfer and differences in density below the crust.

Present Solid Earth: Eventually Earth’s surface cooled enough for solid rocks to form. Crust formed during differentiation. Earth’s surface still changing due to heat from Earth’s interior and impacts and interactions with the newly formed atmosphere.

Formation of Earth’s Atmosphere

Original Atmosphere: hydrogen and helium-blown away by solar wind? Earth’s magnetic field may not have been fully developed when Earth formed.

Outgassing released new atmosphere during volcanic eruptions: water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, &ammonia. Solar radiation changed some of the water vapor and ammonia to react leading to release of hydrogen (ended up in space) and oxygen and nitrogen. Some of the oxygen reacted to form ozone in the upper atmosphere. Ozone layer shields the Earth’s surface from UV radiation. Some of the water on Earth’s surface came from collisions of comets, asteroids, but most resulted from outgassing.

Present Atmosphere: Cyanobacteria and early green plants appeared and began to use carbon dioxide during photosynthesis. Oxygen is released as a byproduct of photosynthesis. Fig 5: 78%nitrogen; 21% oxygen; 1% other.

As Earth cooled, water condensed to form rain. Over millions of years the water has cycled from the atmosphere to the oceans. Ocean’s salt content is due to dissolving rocks which are water soluble.

(Fig 6. When ocean water is heated by the sun, water evaporates leaving salt.) Oceans moderate global temperatures. Oceans can dissolve carbon dioxide, but there’s a limit.

Early Models of the Solar System (p 691)

Aristotle (Greek philosopher): proposed geocentric solar system. Ptolomy (Greek philosopher) (130) used epicycles (small circles) to explain why planets “moved backwards” in geocentric orbits around Earth.

Copernicus (Polish astronomer) (1543) proposed a heliocentric solar system. Galileo Galilei (using a telescope) observed 4 moons orbiting Jupiter; confirmed that objects don’t have to orbit Earth.

Tycho Brahe (Danish astronomer) made detailed observations of the solar system before he died. His assistant, Johannes Kepler, discovered patterns to the observations and developed 3 laws which explained the motion of planets.

Kepler’sLaws:

1) Law of Ellipses: Each planet orbits the sun in a path called an ellipse (2 foci, one of which has the Sun at the center) whose eccentricities differ. (Eccentricity defines how noncircular the ellipse is.)

2) Law of Equal Areas: equal areas are covered in equal amounts of time as an object orbits the sun. (See fig 2, p693. Halley’s comet moves fast when it’s close to the sun but slowly when it’s farther away. A line from the center of the sun to the center of an object sweeps through equal areas in equal periods of time. Ex: 2313 days.)

Law of Periods: The cube of the average distance (a) of a planet from the sun is always proportional to the square of the orbital period (p). Orbital period=how long it takes for a planet to orbit the sun. [pic]

The longer the orbital period, the farther the planet is from the sun. (Sample calc for Jupiter@ end of p 693.)

Isaac Newton’s Explanation of Kepler’s Laws

Inertia keeps objects moving with the same speed and direction unless acted on by a force.

The balanced forces of gravity and inertia keep planets in stable orbits. Outer planets are less attracted by the gravity of the sun than inner planets, so their orbits are curved more gently and they have longer periods of revolution.

Newton’s law of universal gravitation:

[pic]

When distance doubles, F[pic] by factor of____

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