Ch. 28Our Solar System

Formation of Solar System• Big Bang Nebular theory• Particles Planetesimals Planets• Gas giants: collisions of planetesimals made of lighter

elements found further from Sun, big b/c gravitational pull will attract more materials

• Jupiter (biggest) formed first and gathered much of the materials, rings=disks of gas (result: rest of gas giants smaller in size)

• Terrestrial planets: closer to Sun, made of elements that resist vaporization so are rocky & dense

• Leftovers=comets, asteroid belt (couldn’t form planet due to Jupiter’s gravity

Zones of Solar System:1. Terrestrial planets2. Gas giants 3. Kuiper belt: small, icy balls of frozen gases

leftover from Big Bang

Is this to scale?Relative Sizes of Distance Between Planets Planets

•Watch this video clip to help you imagine distances in space…•Why is difficult to make working models of space using the same scale for sizes of planets AND distances between them? •MAKE A MODEL!

stars

Sizes

Distances (1.2 km Ithaca, NY)

Physics and Motion: Models1. Geocentric model: 100 BC; Earth-centered

model (everything in solar system orbited Earth).– Discarded: couldn’t explain…retrograde motion of planets– Retrograde motion: APPARENT backward

movement of a planet due to different/unlike orbital speeds of planets

(37 pictures each 1 week apart; Mars)

Retrograde Motion: Mars

Physics and Motion2. Heliocentric model: 1543; Nicolaus Copernicus; Sun-centered

model inner planets move faster because proximity to Sun greater gravitational pull!

- explained retrograde motion planets closer to Sun faster =orbit more

– Confirmed by Tycho Brahe & Johannes Kepler• Brahe: star observations/planets positions• Kepler: each planet’s orbit Sun in an ellipse shape

Terms to know:

-Ellipse: oval shape fixed on two points

-Semimajor axis: half of the major axis = average distance between Sun and planet

-Astronomical unit: 1.496 X 108 km, Earth’s average distance from Sun, used frequently for space distances [Au]

Kepler’s Laws of Planetary Motion1st Law:

• The Sun is not at the center of the ellipse, but is instead at one focus (generally there is nothing at the other focus of the ellipse). •The planet then follows the ellipse in its orbit, which means that the Earth-Sun distance is constantly changing as the planet goes around its orbit. •For purpose of illustration we have shown the orbit as rather eccentric; remember that the actual orbits are much less eccentric than this.

Kepler’s Laws of Planetary Motion

•The line joining the Sun and planet sweeps out equal areas in equal times, so the planet moves faster when it is nearer the Sun.

-Thus, a planet executes elliptical motion with constantly changing angular speed as it moves about its orbit. -The point of nearest approach of the planet to the Sun is termed perihelion; the point of greatest separation is termed aphelion. -Hence, by Kepler's second law, the planet moves fastest when it is near perihelion and slowest when it is near aphelion.

Ex: Think about the motorcycle races at an amusement park or circus…

2nd Law:

Kepler’s Laws of Planetary Motion

• The squares of the periodic times are to each other as the cubes of the mean distances.

WHOA!…The time a planet takes to complete one orbit is related to its average distance from the Sun.

P= time measured in Earth years

a= length of semimajor axis measured in Au

3rd Law:

P2=a3

Galileo Galileo!• Galileo Galilei: first person to use telescope to

observe sky.– Supported Copernicus’s ideas– Four moons orbit Jupiter this proved that not

all celestial bodies orbit Earth Earth not center of solar system.

– Underlying explanation for heliocentric model remained unknown until Isaac Newton published his law of universal gravitation!

Newton’s Law of Universal Gravitation• Force between objects determined by:– Masses– Distance between them

• Planets/moons constantly “fall” towards object they orbit (otherwise no orbit!)– Downward acceleration produced by gravity!

Newton’s Univ. Gravitational Equation m1m2

r2

F = Force (in Newtons)

G = gravitational constant; always stays the same (6.6726 x 10-11 m3/kg.s2)

m1

and m2

= masses of bodies in kilograms

r= distance between the two bodies in meters

GF =

• This attractive force explains Kepler’s Laws–Moon’s direction changes because

of gravitational attraction of Earth Moon is constantly “falling towards Earth”

• Center of mass: point between planet and Sun around which a planet orbits

—Center of mass is VERY close to Sun because it’s SO massive (see next slide)

Trying to perfectly balance a large child and a small child on a teeter-totter. If the teeter-totter is

suspended in the center, the larger child will be on the ground, but if you move the larger child very close to the center, both children will be in perfect balance.

Solar System

Chapter 28

Planet: large, round heavenly body that orbits a star and shines with light reflected from the star.

Mercury• Closest to sun • One day equals 2/3 of one year (2 yrs=3 days)• Largest day/night temp differences• Scarps: cliffs, when Mercury’s crust

shrank & broke early in geologic history

Venus• Retrograde rotation: rotates clockwise– Sun would appear to rise in west, set in East– Early collision reversed rotation??

• Very dense atmosphere…as if you were 2700 ft underwater!!

• V. efficient greenhouse effect making it the hottest planet

Earth• Most dense• Most tectonically active• Only planet w/plate tectonics• Water in solid, liquid, gas forms

Mars• Constant wind and dust storms• Ancient volcanoes, canyons• Dried riverbeds suggest water in

history?, ice caps at poles

Jupiter• Largest w/diameter 1/10th the Sun• Mass=70% of all planetary matter in solar sys• High albedo (amt of sunlight reflected off a

surface), faint rings, 60 moons (Io, Europa)• Banded b/c of flow in atmosphere due to rotation

(belts: dark, sinking and zones: light, rising)• Great Red Spot=300 yo atmospheric storm• Shortest day (10hrs)• Low density for its size

Saturn• Layered cloud system• Magnetic field is 1000 times stronger than E.• Thin rings of ice chunks (leftovers from

collisions or broken apart moons)• 55 satellites…Titan largest

Uranus• Methane gas in atmosphere gives blue color• Small, solid core surrounded by fluid• 27 moons, very faint ring system • Rotational axis lies almost in orbital plane– Each pole spends 42 Earth yrs in darkness then 42

Earth years in light– Collision w/asteroid?

Neptune• Radius 4X Earth, smaller & denser than Uranus• Distinct clouds, belts and zones• Great Dark Spot (storm, disappeared in 1994)• 13 moons, largest is Triton (retrograde orbit)• 6 rings of microscopic dust particles, don’t

reflect light well so difficult to see

Dwarf Planets• Characteristics:– Gravity gives it a spherical shape – Must orbit Sun– Has not cleared the area of its orbit of smaller debris

– Is not a satellite (moon)• Ex: Ceres (in asteroid belt), Eris (Kuiper belt)• Pluto: made of rock & ice, highly elliptical orbit (closer

to sun than Neptune at times)

Why do you think Pluto is found at the outer edge of our solar system

when it is a terrestrial ‘planet’?

Leftovers• Asteroids: rocky bodies, pitted/irregular shape

– Called meteoroids in Earth’s atmosphere (-oid=object in space)

– Called meteor when it burns up (“shooting star”) (gets pulled in by E’s gravity)

– Called meteorites when it hits the Earth (-ite=rock)• Kuiper belt: 30-50 AU from Sun, vast disk of objects =/> Pluto. Ex. Eris (2003) • Oort cloud: outermost edge of solar system

– Comets: small, icy, highly eccentric orbits• Within 3 AU of Sun evaporates tail pushed away by Sun radiation comet

tail always away from Sun

– Meteor showers: when Earth passes through comet’s trail

Meteoroid, Meteor, Meteorite...What's the Difference?

Atmosphere

Burns up

Hits Earth

Kuiper Belt

Oort Cloud

Meteoroid

Meteor

Meteorite