1 Structure & Formation of the Solar System What is the Solar System? –The Sun and everything gravitationally bound to it. There is a certain order to the Solar System. This gives us information on its formation. The planets to scale with a portion of the Sun visible in the background.

2 Part 1: Structure of the Solar System All the planets orbit the Sun in the same direction. All the planets orbit within nearly the same plane. Like a disk. Two type of planets –Solid, rocky, small planets close to the Sun (like Earth) –Gaseous, large planets far from the Sun (like Jupiter)

3 The Sun The Sun is a star. It is completely gaseous. It emits light and heat through nuclear fusion in its core. It is by far the largest object in the Solar System. 700 times more massive than all of the other objects in the Solar System put together. It is composed mostly of Hydrogen and Helium gas and traces of many other elements. The Sun spins on its axis counter-clockwise.

4 The Planets In order of increasing distance from the Sun: –Mercury –Venus –Earth –Mars –Jupiter –Saturn –Uranus –Neptune –Pluto

5 The Planets All the planets orbit in the same direction counter- clockwise as seen from above Earth’s North Pole. All the planets spin counter- clockwise too except for Venus, Uranus and Pluto.

6 The Inner or Terrestrial Planets Mercury, Venus, Earth and Mars share certain characteristics: –All are rocky bodies. –All have solid surfaces. –Except for Mercury all have at least a thin atmosphere They are called Terrestrial planets because of their resemblance to Earth.

7 The Outer or Jovian Planets Jupiter, Saturn, Uranus and Neptune share certain characteristics: –All are large, gaseous bodies. –All have very thick atmospheres, with possibly liquid interiors and solid cores –All have rings They are called Jovian planets because of their resemblance to Jupiter.

8 Pluto Pluto is unlike any of the terrestrial or jovian planets. –much farther from the Sun than the terrestrial planets. –much smaller than any jovian planet. –composition is thought to be a mixture of ice and rock It is similar to some of the satellites of the jovian planets and similar to some asteroids.

9 Pluto After more rocky/icy bodies were discovered beyond Neptune’s orbit in the early 2000s… Pluto’s classification was changed from planet to dwarf planet by a vote of the International Astronomical Union in Artist’s conception of detected TNOs.

10 Current Planet Definition 1.Must orbit the Sun 2.Must be massive enough to form a sphere by its own gravity 3.Must have cleared its orbit A.Pluto fails this last criterion: its mass is only 7% of the total mass of objects in its orbit; B.Compare to Earth, which is 1.7 million times the mass of any debris in its orbit

11 Satellites (Moons) Ganymede, Callisto, Io, and Europa. Four of Jupiter’s largest satellites. These were discovered by Galileo Galilei and together are called the Galilean satellites of Jupiter. Most of the planets have satellites. Most of the satellites orbit in the equatorial plane of the planet. Most satellites orbit counter-clockwise. The jovian planets have more than a dozen satellites each.

12 Comets and Asteroids The Solar System is filled with millions of smaller bodies. Comets - composed of ice and rock Asteroids - composed of rock and/or metal There is also dust in space which can be seen in meteor showers

13 Comets and Asteroids Most of the estimated 1 trillion comet nuclei originate in the spherical Oort cloud The remainder likely come from the Kuiper belt, just beyond Neptune’s orbit Most asteroids lie in the Asteroid belt, between the orbits of Mars and Jupiter and beyond Pluto (in the Kuiper Belt)