The Solar System

1
The Solar System

• Planetary Orbits
• Fundamental Physics
• Kepler's Laws

• Comets and Asteroids
• Fundamental Nature
• Impacts and Mass Extinction

• Origins of the Solar System

• Planets
• Overview
• Terrestrial Planets
• Jovian Planets
• Pluto

• Other Planetary Systems
• Methods for Detecting
• Examples

2
Planetary Orbits

• Planets orbit the sun in response to its
  gravitational attraction.

3
Periods

• In addition to orbiting the sun, planets also
  rotate.
• The period of revolution is the time required for
  the planet to complete one orbit.
• The period of rotation is the time required to
  turn once about its axis.
• The rotation period determines the length of the
  planet's day.
• The revolution period determines its year.

4
Types of Rotation

• Most planets rotate in the same sense that they
  revolve around the sun. This is known as
  prograde rotation.
• Two planets (Venus and Uranus) rotate in the
  opposite sense of their revolution. This is
  called retrograde rotation.

Prograde Movie Retrograde Movie
5
Orbital Planes

• Planetary orbits lie in a plane.
• The plane of the earth's orbit is called the
  ecliptic.
• The orbital planes for most planets are very
  close to the ecliptic. The most inclined is
  Pluto's, which has a 17o tilt.

6
Kepler's First Law

• Planetary Orbits are ellipses with the sun at one
  focus.

Perihelion
Aphelion

• Perihelion Point of closest approach to the
  sun.
• Aphelion Point where the planet is most distant
  from the sun.

7
Kepler's Second Law

• A radial line from the planet to the sun sweeps
  out equal areas in equal times.
• Planets move faster as they get closer to the sun
  and more slowly as they move away.

8
3rd Law

• The square of the period of revolution is
  proportional to the cube of distance from the
  sun.
• This happens because as the distance from the sun
  increases, the average orbital speed of the
  planet decreases, while the distance around the
  orbit is also increasing.
• Mercury completes one orbit every 88 days.
• Pluto completes one orbit every 249 years.

9
The Planets

• In order of increasing distance from the sun,
  there are nine named planets

• Mercury
• Venus
• Earth
• Mars

• Jupiter
• Saturn
• Uranus
• Neptune

• Pluto and Beyond

10
Terrestrial Planets

• These planets are
• Mercury
• Venus
• Earth
• Mars

• The bulk of the planet's mass is composed of
  solid materials
• Their atmospheres are fairly shallow (Mercury's
  is practically nonexistent.)
• These planet's are much denser than the jovian
  planets.
• They have few natural satellites. Earth has one
  and Mars has two.

11

Mercury

• Mercury is the closet planet to the sun.
• Its diameter is a little larger than the Moon.
• Surface temperatures at midday can reach 800oF.
• Its rotation period is tidally locked to its
  revolution period in a 32 ratio

12

Venus

• In size and composition, Venus appears similar to
  Earth.
• Its atmosphere is mostly CO2.
• Atmospheric pressure is about 90 X that on Earth.
• Its surface temperature is about 900oF. This is
  hotter than Mercury, and is due to a strong
  greenhouse effect.

13

Earth

• Earth is the largest terrestrial planet, and also
  the densest (due to its large iron core).
• It is the only planet with free oxygen in its
  atmosphere and large amounts of liquid water.
• It is the only planet known to support life.

14

Mars

• The atmospheric pressure on Mars is only about 1
  that on Earth.
• It has no liquid water at present.
• Its polar caps grow and shrink with the seasons.
  They are composed of solid carbon dioxide and
  aren't very thick.

15
Jovian Planets

• Jupiter
• Saturn
• Uranus
• Neptune

• The atmosphere's of these planets are a sizable
  fraction of its diameter (Solid surfaces may not
  exist).
• They are composed mostly of hydrogen and helium.
• All have rings and satellite systems that are
  much more extensive than the terrestrial planets.

16

Jupiter

• Jupiter is the largest planet in the solar
  system.
• Its mass is about 1 of the suns mass.
• A prominent feature on Jupiter is the Great Red
  Spot, a cyclonic storm (hurricane) that has
  persisted for hundreds of years (at least).

17

Saturn

• All Jovian planets have rings, but Saturn's are
  the brightest.
• The rings are composed of dust, gravel, and ice.
• Saturn is the least dense of all the planets, its
  density is actually less than water's.

18

Uranus

• Uranus was discovered by William Herschel in
  1781.
• Although difficult to see, its atmosphere shows
  the same banding as other Jovian planets.
• Uranus has an axial tilt so great (82o), that it
  seems to be rolling on its side as it moves
  around its orbit.

19

Neptune

• Neptune's existence was predicted in advance.
• The prediction was based on its affect on the
  orbit of Uranus.
• Only one spacecraft (Voyager 2) has visited the
  planet. If found a storm (the Great Dark Spot)
  similar to the one on Jupiter.

20

Pluto

• Pluto is the smallest planet in the solar system.
• It was discovered by Clyde Tombaugh in 1930.
• Pluto's orbit is the most elliptical of all the
  planets. At times, it is closer to the sun than
  Neptune.
• Pluto has one satellite, named Charon.

21
A 10th Planet?

• A new object, tentatively known as 2002 UB313 has
  been found in the outer solar system.
• It is approximately 3,000 km in diameter (larger
  than Pluto)

22
Sedna

• Sedna is currently the second most distant object
  in the solar system.
• It has a highly eccentric orbit with a very long
  orbital period (10,500 y).

23
Comets

• Comets are small bodies that contain some dust
  and gravel, but are mostly composed of various
  ices (water, ammonia, methane).
• Most are believe to orbit the sun in a region far
  beyond Pluto's orbit, called the Oort cloud.
• These are too small to be seen directly.

24
Visible Comets

• A few comets are in highly eccentric orbits that
  bring them fairly close to the sun.
• When these get close to the sun, some of the ices
  evaporate to form the comet's tail.

25
Famous Comets

• The most famous comet is Halley's comet, which
  returns to the inner solar system every 76 years.
• Two recent visitors Hyatuke-2 (1995) and
  Hale-Bopp (1997) have orbital periods of 18,000 y
  and 4,000 y, respectively.

26
Asteroids

• Asteroids are small objects, usually rocky or
  metallic.
• The largest known asteroid is Ceres it is about
  600 miles in diameter.
• The image on the left was taken by the NEAR
  spacecraft.

27
Asteroid Belt

• Most asteriods orbit the Sun in a zone between
  Mars and Jupiter. This zone is called the
  asteroid belt.
• Jupiter's gravity occasionally can eject
  asteroids from this zone.

28
Near Earth Asteroids

• Some asteroids have orbit that cross the Earth's
  orbit.
• Many of these are known, but most go undetected
  until they actually collide with Earth.

29
Meteors

• Most colliding objects are so small that they
  burn up in the atmosphere before reaching the
  ground.
• These objects are called meteors.

30
Meteorites

• A few objects are large enough to survive until
  atmospheric friction slows them to a reasonable
  speed.
• These impact the ground as meteorites.
• Main meteorite types are
• Nickel-iron
• Chondrite (stoney)
• Carbonaceous Chondrite

Iron Chondrite Carbonaceous Chrondrite
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Destructive Impacts

• Large object (gt100 ft diameter) carry as much
  kinetic energy as an H-bomb.
• Chrondite objects (and comets) generally explode
  at high altitudes.
• Iron objects will reach the ground.
• In both cases, the impacts can be highly
  destructive.

32
Barringer Site

• About 50,000 years ago, a nickel-iron meteorite
  struck the earth near Winslow, Arizona.
• It was about 150 ft across and its speed was
  about 40,000 mph.

33
Barringer Crater

• The impact was equivalent to the explosion of a
  25 megaton H-bomb.
• The resulting crater is 4,000 ft across and 700
  ft deep.

Vistor center
34
Tunguska Event

• At 717 a.m. On June 30, 1907, the earth was
  struck by an object near the Tunguska river in
  Siberia.
• The explosion was equivalent to a 15 megaton
  H-bomb.
• Because no crater has been found, the object is
  thought to be a chondrite or comet.

35
Large Impacts

• Although rare, really large objects (gt 1 km) have
  occasionally struck the earth.
• Energies released in these impacts are much
  larger than any H-bomb.
• The largest of these may be responsible for some
  episodes of mass extinction.

36
Mass Extinctions

• Geologist divide the Earth's past history into
  eras based on the fossils they find.
• Major divisions occur when large numbers of
  extinctions occur simultaneously.

37
The K-T extinction

• The K-T extinction occurred at the end of the
  Cretaceous period about 65 million years ago.
• Between 50-70 of all species were wiped out at
  this time.

38
K-T Boundary

• The boundary between the Cretaceous and Tertiary
  periods is marked by a thin layer of iridium-rich
  clay.
• No dinosaur fossils are found above this layer.
• While iridium is rare in Earth's crust, it is
  much more abundant in nickel-iron meteorites.

Guibo, Italy site Raton, NM site
39
The Cause

• 65 million years ago, the Earth was struck by a
  nickel iron meteorite about 10 km in diameter.
• The impact site was on the continential shelf
  near the area that is now the Yucutan peninsula
  in Mexico.

40
The Effects

• The energy released in the impact was about 5
  trillion megatons!
• The resulting crater now called Chixulub is
  between 150 and 200 miles across.
• The impact severely disrupted world ecology for
  thousands of years.

41
Origins

• The current theory about the origin of the solar
  system is called the protoplanet hypothesis.
• In this theory, the planets formed as a
  by-product of the process that formed the sun.

42
The Nebula

• The solar system formed from a large rotating
  cloud of dust and gas (a nebula).
• Some unknown external event, possibly the
  shockwave from a nearby supernova, compressed the
  cloud and caused it to collapse.

43
Birth of the sun

• As the cloud collapses, gravity would flatten it
  into a disk.
• As it contracts, it would spin faster, but the
  sense of the spin would not change.
• Eventually, the center of the cloud becomes so
  hot and dense that hydrogen fusion begins in its
  core. This is how the sun formed.

44
Formation of the Terrestrial Planets

• Planets form from secondary concentrations of
  material.
• The newly formed sun would drive most of the
  hydrogen and helium out of the inner parts of the
  cloud.
• The inner planets are therefore deficient in
  these materials.

45
Birth of the Jovian Planets

• The jovian planets formed in regions cool enough
  to retain hydrogen and helium.
• These planets are therefore larger than the inner
  planets, because of the relative abundances of
  these substances.

46
Supporting Evidence

• All planets revolve and most rotate in the same
  sense as the sun's rotation. This is a relic of
  the cloud's original rotation.
• Planets and satellites that retain their original
  surfaces are heavily cratered. This is a result
  of the last stages of the accretion process.

47
More Evidence

• Dusty disks have been identified around young
  stars using infrared light.
• These appear to be solar systems that are now
  forming.

48
Other Solar Systems

• Current technology does not make it possible to
  directly image a planet orbiting another star.
• Methods of detecting other solar systems rely on
  the effect of a planet's gravity on the star.

49
Detection Methods

• Direct observation of a star's motion in the sky
  has so far not produced conclusive evidence of
  other planets.
• Doppler shifts in the light emitted by the star,
  however, have found many examples.
• The latter method can give the planet's mass and
  the period of its orbit, and its probable
  distance from the star.

50
Examples

• The first confirmed extra-solar planet orbits the
  star 51 Pegasi. It has a mass about ½ of
  Jupiters and an orbital period of 4 days!
• A planet with 9 times Jupiter's mass orbits the
  star 70 Virginis with a period of 161 days.
• A planet with 3 times Jupiter's mass orbits 47
  Ursa Majoris with a period of 3 years.
• Currently, there are 101 known planets in 88
  systems, with 11 stars known to have multiple
  planets.