Appendix 2: Solar System Extrema

Here are listed the largest, smallest, brightest and densest of the major bodies in the solar system and those with best prospects for life.

The Largest

There are 17 bodies in the solar system whose radius is greater than 1000 km.
[big worlds]
This composite shows the Sun and the 5 largest planets at a scale of 3200 km/pixel. (Earth is the tiny spot between Jupiter and the Sun).
[small worlds]
This composite shows Earth and the remaining 11 large solar system objects at a scale of 100 km/pixel. 
                   Distance   Radius    Mass
 Name       Orbits (000 km)    (km)     (kg)
---------  ------- --------  -------  -------
Sun                           697000  1.99e30
Jupiter    Sun       778000    71492  1.90e27
Saturn     Sun      1429000    60268  5.69e26
Uranus     Sun      2870990    25559  8.69e25 *
Neptune    Sun      4504300    24764  1.02e26 *
Earth      Sun       149600     6378  5.98e24
Venus      Sun       108200     6052  4.87e24
Mars       Sun       227940     3398  6.42e23
Ganymede   Jupiter     1070     2631  1.48e23 +
Titan      Saturn      1222     2575  1.35e23 +
Mercury    Sun        57910     2439  3.30e23 +
Callisto   Jupiter     1883     2400  1.08e23
Io         Jupiter      422     1815  8.93e22
Moon       Earth        384     1738  7.35e22
Europa     Jupiter      671     1569  4.80e22
Triton     Neptune      355     1353  2.14e22
Pluto      Sun      5913520     1160  1.32e22

*Note: Neptune is slightly denser than Uranus.

+Note: Mercury is much denser than Ganymede and Titan.

The Smallest

There are 13 moons whose radius is less than 20 km: 
                   Distance   Radius    Mass
 Name       Orbits (000 km)    (km)     (kg)
---------  ------- --------  -------  -------
Deimos     Mars          23        6  2.00e15
Leda       Jupiter    11094        8  5.68e15
Adrastea   Jupiter      129       10  1.91e16 *
Pan        Saturn       134       10     ?   
Phobos     Mars           9       11  1.08e16 *
Calypso    Saturn       295       13     ?   
Cordelia   Uranus        50       13     ?   
Ananke     Jupiter    21200       15  3.82e16
Atlas      Saturn       138       15     ?   
Telesto    Saturn       295       15     ?   
Helene     Saturn       377       16     ?   
Ophelia    Uranus        54       16     ?   
Sinope     Jupiter    23700       18  7.77e16

*Note: Adrastea is much denser than Phobos.

Of course, there are thousands of smaller asteroids and comets.

The Brightest

There are 12 major bodies brighter than magnitude 6 (as viewed from Earth). All of these can be seen with the unaided eye or with binoculars. 
                   Distance   Radius
 Name       Orbits (000 km)    (km)     Vo *
---------  ------- --------  -------   ---
Sun        ?              0   697000 -26.8
Moon       Earth        384     1738 -12.7
Venus      Sun       108200     6052  -4.4 
Jupiter    Sun       778000    71492  -2.7 
Mars       Sun       227940     3398  -2.0 
Mercury    Sun        57910     2439  -1.9 
Saturn     Sun      1429000    60268   0.7 
Ganymede   Jupiter     1070     2631   4.6 
Io         Jupiter      422     1815   5.0 
Europa     Jupiter      671     1569   5.3 
Uranus     Sun      2870990    25559   5.5 
Callisto   Jupiter     1883     2400   5.6

*Note: Vo = Object's magnitude in visible light at opposition.

Note: Comets are often quite bright during their brief passage near the Sun.

Warning: Do NOT look directly at the Sun. Looking directly at the Sun can cause severe eye damage; doing so with binoculars or a telescope can cause permanent blindness.

The Densest

There are 11 major bodies whose density is greater than 3 g/cm3: 
           Radius    Mass
Name        (km)     (kg)   Dens *
--------- -------  -------  ----
Earth        6378  5.97e24  5.52
Mercury      2439  3.30e23  5.42
Venus        6052  4.87e24  5.26
Adrastea       10  1.91e16  4.5 
Mars         3398  6.42e23  3.94
Io           1815  8.93e22  3.53
Moon         1738  7.35e22  3.34
Elara          38  7.77e17  3.3 
Sinope         18  7.77e16  3.1 
Lysithea       18  7.77e16  3.1 
Europa       1569  4.80e22  3.01

*Note: Density is in grams per cubic centimeter.

Note: Data for the smaller satellites are not very accurate.

There are also many dense asteroids, especially the M-types.

The Best Prospects for Life

     Name  Why
---------  -------
Earth      :-)
Mars       most Earth-like; more so in the past; ALH84001
Europa     may have liquid water
Enceladus  may have liquid water
Titan      complex chemistry and liquids likely
Io         complex chemistry, warmer than most
Jupiter    long shot: warm, plenty of organic material

The Mars meteor results notwithstanding, all of this remains very speculative. None of these prospects are really very good. Good arguments can be made why life (at least life as we know it) cannot exist on any of these bodies. (More speculation about life on Europa and Enceladus.)

Contents ... Appendices ... Data ... Extrema ... Chronology ... Host
Bill Arnett; last updated: 1997 Jan 4