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| Science | Astronomy | Planets (1) | Planets | Dwarf Planets | Satellites (Moons) |
This page lists the basic characteristics of the planets and other major bodies of the Solar System. For details of their atmosphere, surface and interior structure, see Planets (2). For anything else, see Solar System.
... in order of the radii of their orbits around the Sun – in other words, their distances from the Sun:
| Name | Discovered | By | Relative Mass | Diameter (miles) | Mean radius of orbit (miles) | Rotational period ('day') | Orbital period ('year') | Satellites (known in November 2018) |
| Mercury | 0.056 | 3,030 | 36,000,000 | 59 | 88 days | None | ||
| Venus | 0.82 | 7,500 | 67,200,000 | 243 | 225 days | None | ||
| Earth | 1 | 7,923 | 92,860,000 | 1 | 365.24 days | The Moon (see below) | ||
| Mars | 0.11 | 4,210 | 141,600,000 | 1.02 | 687 days | Phobos, Deimos (see below) | ||
| Jupiter | 318 | 88,700 | 484,000,000 | 9hr 51min | 11.86 years | 79 (Ganymede is the largest) | ||
| Saturn | 95 | 75,000 | 866,000,000 | 10hr 14m | 29.46 years | 62 (Titan is the largest) | ||
| Uranus | 1781 | William Herschel | 14.5 | 31,600 | 1,800,000,000 | 17hrs 24min | 84 years | 27 (named after Shakespearean characters) |
| Neptune | 1846 | J. G. Galle | 17.2 | 30,200 | 2,794,000,000 | 16hr 7min | 164.8 years | 14 (2 are visible from Earth) |
Twelve new moons of Jupiter were discovered in July 2018.
The four largest moons of Jupiter (Io, Europa, Ganymede and Callisto) were discovered in 1610 by Galileo Galilei and are known as the Galilean satellites. They were the first celestial objects to be discovered by telescope.
... in order of discovery:
| Name | Discovered | By | Relative Mass | Diameter (miles) | Mean radius of orbit (miles) | Rotational period ('day') | Orbital period ('year') | Satellites |
| Ceres | 1801 | Giuseppe Piazzi | 0.00016 | 590 | 256,000,000 | 9 hours | 1,680 days | |
| Pluto | 1930 | Clyde Tombaugh | 0.002 | 1,438 | 3,600,000,000 | 6.39 days | 248.5 years | Charon (see below), Nix, Hydra |
| Eris | 2003 | Mike Brown | Unknown | 1,490 | 6,288,000,000 | > 8 hours? | 556 years | Dysnomia |
| Sedna | 2003 | Mike Brown | 5.6 * 10–4 | 1,100 | 17,000,000,000 | 10 hours | 11,487 years | |
| Makemake | 2004 | Mike Brown | 0.0005 | 450 | 4,278,000,000 | Unknown | 310 years | None so far |
| Haumea | 2005 | Mike Brown | 0.00066 | 400 | 3,900,000,000 | 3.9 hours | 283 years | Hi'iaka, Namaka |
Note: the IAU does not currently classify Sedna as a dwarf planet, although many astronomers do. Officially it's a minor planet, or a Trans–Neptunian Object (TNO).
This section lists the ten most significant satellites or moons in the Solar System (the ones you're most likely to get asked about in a quiz.) For which satellite belongs to which planet, see the Planets table above. But for the record: Titan belongs to Saturn, and the other four biggest ones (other than The Moon) belong to Jupiter; Triton belongs to Neptune, Charon belongs to Pluto, and Phobos and Deimos both belong to Mars.
| Name | Discovered | By | Relative Mass | Diameter (miles) | Mean radius of orbit (miles) | Rotational period ('day') | Orbital period ('year') | Satellites |
| Ganymede | 1610 | Galileo Galilei | 0.025 | 3,270 | 700,000 | Synchronous | 7.2 days | The ninth largest object in the solar system |
| Titan | 1655 | Christiaan Huygens | 0.023 | 3,200 | 759,000 | Synchronous | 15.95 days | The only 'moon' with an atmosphere (nitrogen) |
| Callisto | 1610 | Galileo | 0.018 | 3,000 | 1,170,100 | Synchronous | 16.7 days | |
| Io | 1610 | Galileo | 0.015 | 2,250 | 262,100 | Synchronous | 1.8 days | |
| The Moon | 0.012 | 2,160 | 238,855 | Synchronous | 27.32 days * | |||
| Europa | 1610 | Galileo | 0.008 | 1,950 | 417,000 | Synchronous | 3.6 days | |
| Triton | 1846 | William Lasell | 0.0036 | 1,680 | 220,400 | Synchronous | –5.877 days | The only large moon with a retrograde orbit |
| Charon | 1978 | James W. Christy | 3 * 10–5 | 1,200 | 12,500 | Synchronous | 6.39 days | |
| Phobos | 1877 | Asaph Hall (US) | 5.6 * 10–9 | 17 | 5,840 | Synchronous | 0.32 days | Irregularly shaped – diameter given is largest |
| Deimos | 1877 | Asaph Hall (US) | 3.8 * 10–10 | 9 | 15,000 | Synchronous | 1.26 days | Irregularly shaped – diameter given is largest |
* 27 days, 7 hours, 41 minutes. The 'lunation period' – the time taken to complete the lunar
cycle of phases – is 29.53 days
© Haydn Thompson 2017–20