Learning objectives
Note: As this book goes to press, over four hundred moons are now known in the solar system and more are being discovered on a regular basis. Of the major planets, only Mercury and Venus do not have moons. In addition to moons of the planets, there are many moons of asteroids. In this appendix, we list only the largest and most interesting objects that orbit each planet (including dwarf planets). The number given for each planet is discoveries through 2024. For further information see https://science.nasa.gov/solar-system/moons and https://en.wikipedia.org/wiki/List_of_natural_satellites.
| Selected Moons of the Planets | |||||||
|---|---|---|---|---|---|---|---|
| Planet (moons) | Satellite Name | Discovery | Semimajor Axis (km × 1000) | Period (d) | Diameter (km) | Mass (1020 kg) | Density (g/cm3) |
| Earth (1) | Moon | — | 384 | 27.32 | 3476 | 735 | 3.3 |
| Mars (2) | Phobos | Hall (1877) | 9.4 | 0.32 | 23 | 1 × 10−4 | 2.0 |
| Deimos | Hall (1877) | 23.5 | 1.26 | 13 | 2 × 10−5 | 1.7 | |
| Jupiter (95) | Amalthea | Barnard (1892) | 181 | 0.50 | 200 | — | — |
| Thebe | Voyager (1979) | 222 | 0.67 | 90 | — | — | |
| Io | Galileo (1610) | 422 | 1.77 | 3630 | 894 | 3.6 | |
| Europa | Galileo (1610) | 671 | 3.55 | 3138 | 480 | 3.0 | |
| Ganymede | Galileo (1610) | 1070 | 7.16 | 5262 | 1482 | 1.9 | |
| Callisto | Galileo (1610) | 1883 | 16.69 | 4800 | 1077 | 1.9 | |
| Himalia | Perrine (1904) | 11,460 | 251 | 170 | — | — | |
| Saturn (274) | Pan | Voyager (1985) | 133.6 | 0.58 | 20 | 3 × 10−5 | — |
| Atlas | Voyager (1980) | 137.7 | 0.60 | 40 | — | — | |
| Prometheus | Voyager (1980) | 139.4 | 0.61 | 80 | — | — | |
| Pandora | Voyager (1980) | 141.7 | 0.63 | 100 | — | — | |
| Janus | Dollfus (1966) | 151.4 | 0.69 | 190 | — | — | |
| Epimetheus | Fountain, Larson (1980) | 151.4 | 0.69 | 120 | — | — | |
| Mimas | Herschel (1789) | 186 | 0.94 | 394 | 0.4 | 1.2 | |
| Enceladus | Herschel (1789) | 238 | 1.37 | 502 | 0.8 | 1.2 | |
| Tethys | Cassini (1684) | 295 | 1.89 | 1066 | 6.2 | 0.98 | |
| Dione | Cassini (1684) | 377 | 2.74 | 1120 | 11 | 1.3 | |
| Rhea | Cassini (1672) | 527 | 4.52 | 1530 | 25 | 1.3 | |
| Titan | Huygens (1655) | 1222 | 15.95 | 5150 | 1346 | 1.9 | |
| Hyperion | Bond, Lassell (1848) | 1481 | 21.3 | 270 | — | — | |
| Iapetus | Cassini (1671) | 3561 | 79.3 | 1435 | 19 | 1.2 | |
| Phoebe | Pickering (1898) | 12,950 | 550 (R)R stands for retrograde rotation (backward from the direction that most objects in the solar system revolve and rotate). | 220 | — | — | |
| Uranus (29) | Puck | Voyager (1985) | 86.0 | 0.76 | 170 | — | — |
| Miranda | Kuiper (1948) | 130 | 1.41 | 485 | 0.8 | 1.3 | |
| Ariel | Lassell (1851) | 191 | 2.52 | 1160 | 13 | 1.6 | |
| Umbriel | Lassell (1851) | 266 | 4.14 | 1190 | 13 | 1.4 | |
| Titania | Herschel (1787) | 436 | 8.71 | 1610 | 35 | 1.6 | |
| Oberon | Herschel (1787) | 583 | 13.5 | 1550 | 29 | 1.5 | |
| Neptune (16) | Despina | Voyager (1989) | 53 | 0.33 | 150 | — | — |
| Galatea | Voyager (1989) | 62 | 0.40 | 150 | — | — | |
| Larissa | Reitsema, et al (1981) | 74 | 0.55 | 194 | — | — | |
| Proteus | Voyager (1989) | 118 | 1.12 | 420 | — | — | |
| Triton | Lassell (1846) | 355 | 5.88 (R)R stands for retrograde rotation (backward from the direction that most objects in the solar system revolve and rotate). | 2720 | 220 | 2.1 | |
| Nereid | Kuiper (1949) | 5511 | 360 | 340 | — | — | |
| Pluto (5) | Charon | Christy (1978) | 19.7 | 6.39 | 1200 | — | 1.7 |
| Styx | Showalter et al (2012) | 42 | 20 | 20 | — | — | |
| Nix | Weaver et al (2005) | 48 | 24 | 46 | — | 2.1 | |
| Kerberos | Showalter et al (2011) | 58 | 24 | 28 | — | 1.4 | |
| Hydra | Weaver et al (2005) | 65 | 38 | 61 | — | 0.8 | |
| Eris (1) | Dysnomea | Brown et al (2005) | 38 | 16 | 684 | — | — |
| Makemake (1) | (MK2) | Parker et al (2016) | — | — | 160 | — | — |
| Haumea (2) | Hi’iaka | Brown et al (2005) | 50 | 49 | 400 | — | — |
| Namaka | Brown et al (2005) | 39 | 35 | 200 | — | — | |