AAQ Solar System Section

An Introduction To The Solar System

The Solar System consists of the Sun and the objects that orbit around it. It is located in one of the spiral arms of our home galaxy, the Milky Way, at a distance in the order of 27,000 light years (ly; 1 ly = 9.46 x 1012 km) from galactic centre and about 20 ly above the galactic equatorial plane. The Solar System is estimated to be about 4.6 billion years old. The exact size of the Solar System is not known but is estimated to be in the order of 2.5 ly in diameter. Approximately 99.85% of all the mass in the Solar System is located in the Sun with the nine planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto) accounting for another 0.135% of the total mass. The remaining mass is tied up in the various satellites of the planets, asteroids, comets and interplanetary matter. The planets orbit the Sun on elliptical paths with the Sun at one focus point of the ellipse (Kepler’s First Law Of Planetary Motion) with all orbits in a similar plane to that defined by the orbit of the Earth around the Sun called the ecliptic.

A simplified classical description of the Solar System divides it into the following zones centred on the Sun:

• Terrestrial Planets (Mercury, Venus, Earth and Mars): small planets composed predominantly of silicates and metals with a rocky or solid surface and few satellites, located 0.3 – 1.7 Astronomical Units (AU; 1 AU = 1.496 x 108 km) from the Sun;

• Asteroid Belt: composed of numerous asteroids - rocky, metallic and icy bodies up to 1000 km in diameter. The majority, but not all asteroids, also called minor planets, orbit between Mars and Jupiter at a distance of 2 – 4 AU from the Sun;

• Gas Giants or Jovian Planets (Jupiter, Saturn, Uranus and Neptune): large planets composed predominantly of hydrogen and helium with extensive atmospheres located 5 – 30 AU from the Sun;

• Kuiper Belt or Trans Neptunian Objects: small icy (asteroidal / cometary) bodies, of which the largest and best known is the planet Pluto, located 30 – 500 AU from the Sun;

• Oort Cloud: a hypothesised spherical region of numerous small icy bodies located 50,000 – 100,000 AU from the Sun and the source of long period comets.

Note that the Solar System is actually more complex than the above description and solar system models are being continually revised as more information is obtained on our nearest neighbours.

Some basic facts on our Sun and the planets are presented below.

Object

Distance From Sun
(AU)

Equatorial Diameter
(km)

Mass
(No. of Earths)

Density
(kg/m 3)

Sideral Period
(Earth years)

Rotational Period
(Earth days)

Inclination To Ecliptic
(degrees)

Inclination Of Rotational Axis
(degrees)

Number Of Satellites

Brightness
(apparent magnitude)

Angular Size
(arc seconds)

Sun

-

1,392,530

332946

1409

-

25 - 36

-

7.25

9 planets + asteroids & comets

-26.8

1896 – 1962

Mercury

0.30 – 0.47

4,879

0.06

5430

0.24

58.65

7.00

0

0

3.1 -
-2.1

4.7 – 12.1

Venus

0.72 – 0.73

12,104

0.82

5240

0.62

243.02
retrograde

3.39

177.36

0

-3.9 -
-4.7

9.7 – 61.6

Earth

0.98 – 1.02

12,756

1.00

5520

1.00

1.00

0

23.45

1

-

-

Mars

1.38 – 1.66

6,794

0.11

3940

1.88

1.03

1.85

25.18

2

1.8 -
-2.9

3.5 – 25.1

Asteroids

0.19 -18.50  

 < 940

 < 0.0002

1300 - 3800  

~ 0.3 - 60  

 0.12 - 0.71

 0 - 64

- 

- 

 > 5.9

< 1.0  

Jupiter

4.95 – 5.45

142,984

317.94

1330

11.86

0.41

1.31

3.12

63

-1.7 -
-2.7

30.6 – 50.0

Saturn

9.00 – 10.07

120,536

95.20

690

29.46

0.43

2.49

26.74

35

0.3 -
-0.5

16.5 – 20.6

Uranus

18.28 – 20.08

51,118

14.54

1290

84.01

0.72
retrograde

0.77

97.87

27

5.9 – 5.7

3.4 – 3.7

Neptune

29.79 – 30.33

49,500

17.14

1640

164.79

0.67

1.77

29.56

13

8.0 – 7.8

2.2 – 2.4

Pluto

29.57 – 49.30

2,302

0.002

2040

248.54

6.39
retrograde

17.15

120.05

1

14.0 - 13.8

0.1

Comets
(nucleus)

 < 1 - 100,000

 < 20

< 10e-10  

 ~ 1000

 > 3.3

 -

 0 - 90

 -

 0

 > 1

 < 0.2

For further information on the Solar System visit the following excellent web sites.

The Nine Planets - A multimedia tour of the Solar System by Bill Arnett

Solar Views - Views of the Solar System by Calvin J Hamilton

Solar System Exploration - Exploration of the Solar System by NASA

JPL Solar System - Jet Propulsion Laboratory’s information on the Solar System

 

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Astronomical Association of Queensland 2006. www.aaq.org.au