1. The bright star Antares embedded in dust and gases
Introduction to the
Solar System
The bright star Antares embedded in dust and gases

2. Origin of the Solar System
Modern astronomers believe that the sun and planets condensed out of a nebula or large cloud of gas and dust.
This idea is named the Nebular Hypothesis. It was first presented by the German philosopher Immanuel Kant in the late 1700’s.
Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris)

3. The Formation of the Solar System
Our solar system began as a rotating gas cloud or nebula that collapsed toward its center under the influence of gravity.
A condensation formed at the center, which is called a protostar.
A flattened disk of matter surrounded the protostar, which began to shine and become a star, our sun.

4. The Formation of our Solar System
The rising temperature from the sun removed the gas from the inner regions, leaving dust and larger debris
Inner planets formed from solid debris
Outer planets retained original gases
Planets established dominance in their regions of the solar system.
After almost all of the remaining gas, dust, and small debris was collected by the larger objects, the solar system took on the form we recognize today.

5. Other Star Systems Forming
We can look at young star systems developing today.
The planets orbiting these stars are formed from the surrounding disks of gas and dust, called protoplanetary disks or proplyds.
Proplyd in the Orion Nebula

6. Beta Pictoris May represent new solar system in formation
Disk of gas, dust seen edge-on, star Beta in center (covered to reveal faint outer disk)

7. Solar System Composite
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Solar System Composite

8. Common Properties of Planet Orbits in Our Solar System
As viewed from above, all of the planets orbit the Sun in a counterclockwise direction.
The orbital inclination is the angle between a planet’s orbit and the ecliptic.
The planets orbit in nearly the same plane (ecliptic). All planets except Pluto have an orbital inclination of less than 7°.

9. Inner Solar System

10. Outer Solar System

11. Pluto’s Odd Orbit
Pluto’s orbit, or plane of revolution, is tilted by 17° to the general solar system orbits (ecliptic)
Pluto can also cut across Neptune’s orbit (but they can never collide)

12. Ecliptic Plane
Plane of the Ecliptic: The orbits of the planets are mostly in the same plane.
This plane is called the ecliptic and is defined by the plane of the earth’s orbit.
The exception is Pluto, which is tilted quite a bit in comparison to the rest of the planets.
The ecliptic plane is a remnant of the original, rotating nebular disk that formed the sun and planets

13. Ecliptic: Artist’s View

14. Motions
Directions of Motion: The planets orbit in a counterclockwise direction around the sun (when looking down upon the solar system from the sun’s north pole).
All the planets, except for Venus, Uranus, and Pluto, rotate in the same direction as their orbits.

15. SS Revolution
All planets revolve counter-clockwise when viewed from above

16. Orbits
The planets nearest to the Sun (Mercury, Venus, Earth, and Mars) are relatively close together, while those farther away (Jupiter, Saturn, Uranus, and Neptune) are more spread out.
Most of the planets are in nearly circular orbits.

17. Solar System Orbits (AU)
The astronomical unit (AU) is useful in measuring distances in the solar system
One AU equals the average earth-to-sun distance of 93 million miles
AU distances allow direct comparison to the earth which is equal to 1.0
Planet
Distance from the sun in AU
Mercury
0.4
Venus
0.7
Earth
1.0
Mars
1.5
Jupiter
5.2
Saturn
9.5
Uranus
19.2
Neptune 30
Pluto
39.5

19. Revolutions of the Planets*
Mercury 88 days
Venus days
Earth days
Mars 1.88 years
Jupiter years
Saturn 29.5 years
Uranus 84 years
Neptune years
Pluto years
*Earth days and years

21. Diameters Planet Diameter (Earth = 1) Mercury 0.38 Venus 0.95 Earth
1.0
Mars
0.53
Jupiter
11.21
Saturn
9.45
Uranus
4.01
Neptune
3.88
Pluto
0.18

23. Masses Planet Mass (Earth = 1) Mercury 0.06 Venus 0.81 Earth 1.0 Mars
0.11
Jupiter
317.94
Saturn
95.18
Uranus
14.53
Neptune
17.14
Pluto
0.002

25. Average Density (kg/m3)
Planet
Average Density (kg/m3)
Mercury
5430
Venus
5250
Earth
5520
Mars
3950
Jupiter
1330
Saturn
690
Uranus
1290
Neptune
1640
Pluto
2030

27. Rotational Period Planet Days (Earth  1) Mercury 58.6462 Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
6.3872

29. Average Temperature Planet Ave Temp (°F) Mercury 354° Venus 867° Earth
45°
Mars
-81°
Jupiter
-186°
Saturn
-202°
Uranus
-337°
Neptune
-364°
Pluto
-380°

30. Average Temperature (Earth = 1)

31. Sizes of the Planets
In mass, the sun represent 99% of the solar system
The smallest planet, Mercury, has a diameter of 3031 mi
Pluto, the previous smallest planet, has a diameter of 1457 mi
The largest planet, Jupiter, has a diameter of 88,700 mi
Earth = 7926 mi
Ganymede, the largest moon of Jupiter, is larger than Mercury, yet Ganymede is not considered a planet because it revolves around Jupiter

32. Two Basic Groups of Planets
TERRESTRIAL (earth-like)
Small size, low Mass
Higher density
Mostly rock
Mercury, Venus, Earth, Mars
JOVIAN (Jupiter-like)
Large size, massive
Low density
Mostly gas
Jupiter, Saturn, Uranus, Neptune

33. Classifications
Terrestrial or Rocky planets—Composed of rock and metal: Mercury, Venus, Earth, Mars
Jovian or Gas planets—Composed primarily of the gases hydrogen and helium: Jupiter, Saturn, Uranus, Neptune

34. Classification, cont.
Small Planets—Diameters less than 13,000 km: Mercury, Venus, Earth, Mars
Giant Planets (Gas Giants)—Diameters greater than 48,000 km: Jupiter, Saturn, Uranus, Neptune

35. Classification, cont. Inner Planets—Mercury, Venus, Earth, Mars
Outer Planets—Jupiter, Saturn, Uranus, Neptune

36. Classification, cont.
Inferior—Closer to the sun than earth: Mercury and Venus
Superior—Farther from the sun than earth: Mars, Jupiter, Saturn, Uranus, Neptune

37. Classification, cont.
Classical—Known since prehistoric times, visible to the unaided eye: Mercury, Venus, Mars, Jupiter, Saturn
Modern—Discovered in modern times, visible only with telescopes: Uranus, Neptune, (Pluto)

38. Classification Table (fill in your copy and paste this in your notes)
Planet
Rocky or Gas?
Small or Giant?
Inner or Outer?
Inferior or Superior?
Classical or Modern?
Mercury R S I C
Venus
Earth
N/A ?
Mars
Jupiter G O
Saturn
Uranus M
Neptune
Pluto*

39. New Solar System (> 2006)
Planets:
Mercury
Venus
Earth
Mars
Ceres (dwarf)
Jupiter
Saturn
Uranus
Neptune
Pluto (dwarf)
Eris (dwarf)
Makemake (dwarf)
Eris
Two Categories: Planets and Dwarf Planets (dwarfs beyond Neptune are “Plutoids”)
Today’s astronomers recognize only 8 planets

40. Solar System Model
If the sun were an orange, the earth would be a grain of sand thirty feet away.
Jupiter would be a cherry pit located one block from the sun.
Saturn would be another cherry pit located one block from Jupiter.
Pluto would be a grain of sand 10 blocks from the sun.
The nearest star to our sun (Alpha Centauri) would be represented as another orange 2000 miles from the sun.

41. The modern planets, Uranus, Neptune, and Pluto, are also Roman gods
Jupiter from Fantasia (Disney)
Planet Names
The planets have been given the Roman names of gods from ancient Greece.
Roman
Mercury, Venus, Mars, Jupiter, Saturn
Greek
Hermes, Aphrodite, Ares, Zeus, Kronos
The modern planets, Uranus, Neptune, and Pluto, are also Roman gods