Basic Features of the Solar System

1
Basic Features of the Solar System

• The Sun
• By far the largest body in the solar system
• More than 700 times the mass of all other bodies
  put together
• Gravitational force holds the planets and other
  bodies in the system in their orbital patterns
  about it

2
Basic Features of the Solar System

• The planets
• Inner (or Terrestrial) planets
• Mercury, Venus, Earth, Mars
• Small, rocky bodies with relatively thin or no
  atmospheres
• Rocky composed of silicon and oxygen (SiO2) with
  an admixture of other heavy elements such as
  aluminum, magnesium, sulfur, and iron.

3
Basic Features of the Solar System

• The Planets
• The outer (or Jovian) planets
• Jupiter, Saturn, Uranus, Neptune
• Gaseous and Liquid
• Gas giants have deep, hydrogen-rich atmospheres
• No true surface atmospheres thicken with depth
  and eventually liquefy

4
Basic Features of the Solar System

• Other objects
• Satellites
• moons
• Only Mercury and Venus are moonless
• Comets
• Rocky or Icy bodies around 10km or less in
  diameter
• Extremely elliptical orbits
• Long tails of gas and dust
• Originate from Oort Cloud

5
Basic Features of the Solar System

• Asteroids
• Rocky or metallic bodies orbiting sun
• Diameters range from few meters to 1000 km
• Many populate the Asteroid Belt between the
  orbits of Mars and Jupiter
• Most likely asteroids are material that failed to
  form a planet

6
Basic Features of the Solar System

• Dwarf Planets
• Pluto, Ceres, Xena, Sedna
• (a) is in orbit around the Sun
• (b) has sufficient mass for its self-gravity to
  assume a nearly round shape
• (c) has not cleared the neighborhood around its
  orbit and
• (d) is not a satellite
• Binary Planets
• Many scientists belive Pluto and Charon are a
  binary planet

7
Basic Features of the Solar System

• Oort Cloud
• A spherical cloud of comets that completely
  surrounds the Solar System.
• Extends from about 40,000 AU to about 100,000 AU
  from the Sun.
• Possibly up to 100 billion objects inhabit the
  Oort Cloud
• Possibly made up of leftover matter from the
  formation of the Solar System
• Total mass about 100 Earth masses

8
Basic Features of the Solar System

• Kuiper Belt
• Disk-shaped belt of comets and other objects
  around 30-50 AU from the Sun
• Total mass about the same as the Earth
• Pluto believed to be Kuiper Belt object instead
  of a planet by many scientists.
• Sedna and Quaoar are recently discovered Kuiper
  Belt objects similar in size to Pluto.

9
Basic Features of the Solar System

• Orbits of planets
• Nearly circular and nearly on same plane
  (Ecliptic)
• Tilts of Planets
• Most planets tilt less than 30 degrees
• Only Uranus tilts more than 30 degrees.

10
Origin of the Solar System

• Theories
• Nebular hypothesis
• A vast cloud of interstellar gas collapsed to
  form the Sun and planets.
• Once contraction started, the gravitational force
  of the cloud acting on itself would accelerate
  its collapse into a virtually small volume
• Cloud begins to spin faster as it contracts
  (Conservation of Angular Momentum)

11
Origin of the Solar System

• Theories
• Nebular hypothesis
• At some stage, the rotating cloud of gas assumes
  a disklike shape.
• The collapsing mass of gas would leave behind a
  ring of material
• Rings of material would eventually coalesce into
  a planet
• As mass of gas collapsed further, more rings
  would be left behind.

12
Origin of the Solar System

• Theories
• Three fatal flaws of Nebular hypothesis as
  originally presented
• First Difficult to think of a way for gaseous
  material left behind in rings to coalesce into
  planets
• Second The high spin rate needed to throw off
  rings of material would result in a Sun spinning
  must faster than ours.
• Third Does not explain differences between
  Terrestrial and Jovian planets

13
Origin of the Solar System

• Theories
• Collision hypotheses
• One states that the planets formed when a comet
  collided with the Sun
• Another states that a star passing very close to
  the sun pulled gas away that eventually formed
  the planets
• Another states that the Sun was initally part of
  a binary and that a passing star disrupted the
  partner, creating the planets

14
Origin of the Solar System

• Theories
• Accretion hypothesis
• Planets formed by accretion formed from
  interstellar material swept up by the Sun
• Hypotheses differ in the number of stars needed
  and the number of interstellar clouds needed.
• One hypothesis says that the Sun encountered a
  protostar and pulled the required material away.
• None of these theories are accepted today

15
Origin of the Solar System

• Modern Accepted Theories
• Very similar to the nebular hypothesis
• Interstellar gas clouds coalesce into a flattened
  disk
• Differ from original nebular hypothesis in that
  the modern theories throw out the idea of the
  disk forming rings
• Modern theories state that turbulence within the
  disk helps matter condensate into protoplanets

16
Origin of the Solar System

• Modern Accepted Theories
• Dust played a huge part in the formation of
  planets.
• Most scientists believe planets formed from the
  accumulation of dust instead of the collapse of
  gases.
• Temperature differences caused the different
  types of planets (Terrestrial and Jovian) to form
  at different distances from the protosun.