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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 (AU) | Rotational period ('day') | Orbital period ('year') | Satellites (according to NASA, May 2025) |
| Mercury | Known since ancient times | 0.056 | 3,030 | 0.39 | 59 | 88 days | None | |
| Venus | 0.82 | 7,500 | 0.72 | 243 | 225 days | None | ||
| Earth | 1 | 7,923 | 1 | 1 | 365.24 days | The Moon (see below) | ||
| Mars | 0.11 | 4,210 | 1.52 | 1.02 | 687 days | Phobos, Deimos (see below) | ||
| Jupiter | 318 | 88,700 | 5.20 | 9hr 51min | 11.86 years | 97 (Ganymede is the largest) | ||
| Saturn | 95 | 75,000 | 9.54 | 10hr 14m | 29.46 years | 274 (Titan is the largest) | ||
| Uranus | 1781 | William Herschel | 14.5 | 31,600 | 19.22 | 17hrs 24min | 84 years | 28 (named after Shakespearean characters) |
| Neptune | 1846 | J. G. Galle | 17.2 | 30,200 | 30.06 | 16hr 7min | 164.8 years | 16 (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.
The term 'dwarf planet' was coined in 1990 by the American planetary scientist Alan Stern, and the concept was adopted by the IAU in 2006. A dwarf planet is defined (on Wikipedia) as "a small planetary–mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System."
Pluto, discovered in 1930 and previously considered a planet, was 'demoted' in 2006 to become one of the first three dwarf planets, which are:
| Name | Discvrd | By | Mass (kg) | Diameter (km) | Mean radius of orbit (AU) | Rotational period ('day') | Orbital period ('year') | Satellites |
| Ceres | 1801 | Giuseppe Piazzi | 9.38 x 1020 | 939.4 | 2.77 | 9.1 hours | 1,680 days | None |
| Pluto | 1930 | Clyde Tombaugh | 13 x 1021 | 2,377 | 39.48 | 6.39 days | 248.5 years | Charon (see below), Styx, Nix, Kerberos, Hydra |
| Eris | 2003 | Mike Brown | 16.47 x 1021 | 2,326 | 67.86 | 15 days 18.9 hrs | 559 years | Dysnomia |
The following are "generally assumed to be dwarf planets" (according to Wikipedia):
| Makemake | 2004 | Mike Brown | 3.1 x 1021 | 1,430 | 45.56 | 22.8 hours | 307.5 years | One (no informal name) |
| Haumea | 2005 | Mike Brown | 4.01 x 1021 | 1,560 | 43.22 | 3.9 hours | 284.1 years | Hi'iaka, Namaka |
Haumea has one known ring.
The following "meet the preliminary criteria ... for identifying dwarf planets, and are generally called dwarf planets by astronomers as well":
| Quaoar | 2002 | Trujillo & Brown | 1.2 x 1021 | 1,086 | 43.7 | 17.7 hours | 288.8 years | Weywot |
| Sedna | 2003 | Trujillo, Brown, Rabinovitz | 1 x 1021? | 906 | 506.8 | 10 hours | 11,400 years | None known |
| Orcus | 2004 | 5.55 x 1020 | 910 | 39.4 | 13 hours | 247.3 years | Vanth | |
| Gonggong | 2007 | Schwamb, Brown, Rabinowitz | 1.75 x 1021 | 1,230 | 67.49 | 22.4 hours | 554.4 years | Xiangliu |
Quaoar has two known rings.
These details were last updated in May 2025.
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 2017–25