List of gravitationally rounded objects of the Solar System

In 2006, the International Astronomical Union (IAU) defined a planet as a body in orbit around the Sun that was large enough to have achieved hydrostatic equilibrium and to have cleared the neighbourhood around its orbit. An object in hydrostatic equilibrium is one that is large enough for its gravity to have overcome its internal rigidity, and so relax into a rounded (ellipsoidal) shape. The practical meaning of "cleared the neighborhood" is that a planet is comparatively massive enough for its gravitation to control the orbits of all objects in its vicinity. By the IAU's definition, there are eight planets in the Solar System. Those objects in orbit around the Sun that have achieved hydrostatic equilibrium but have not cleared their neighborhoods are called dwarf planets, and the remainder are termed small Solar System bodies. In addition, the Sun itself and a dozen or so natural satellites are also massive enough to have achieved hydrostatic equilibrium. Apart from the Sun, these bodies are included in the term planetary-mass object, or planemo. All known planetary-mass objects in the Solar System, as well as the Sun, are listed below, along with a sample of the largest objects whose shape has yet to be accurately determined. The Sun's orbital characteristics are listed in relation to the Galactic Center. All other objects are listed in order of their distance from the Sun.

Sun

The Sun is a G-type main-sequence star. It contains almost 99.9 percent of all the mass in the Solar System.

		Sun
Astronomical symbol
Mean distance from Galactic Center	km light years	~2.5×1017 ~26,000
Mean radius	km  :E	696,000 109
Surface area	km2  :E	6.0877×1012 11,990
Volume	km3  :E	1.4122×1018 1,300,000
Mass	kg  :E	1.9891×1030 332,946
Gravitational parameter	m3/s2	1.327×1020
Density	g/cm3	1.409
Equatorial gravity	m/s2	274.0
Escape velocity	km/s	617.7
Rotation period	days	25.38
Orbital period about Galactic Center	million years	225–250
Mean orbital speed	km/s	~220
Axial tilt to the ecliptic	deg.	7.25
Axial tilt to the galactic plane	deg.	67.23
Mean surface temperature	K	5,778
Mean coronal temperature	K	1–2×106
Photospheric composition		H, He, O, C, Fe, S

Planets

Key
* terrestrial planet	° gas giant	† ice giant

Planets are both large enough to have achieved hydrostatic equilibrium and have cleared their neighborhoods of similar objects. There are four terrestrial planets (Mercury, Venus, Earth and Mars) and four giant planets, which can be divided further into two gas giants (Jupiter and Saturn) and two ice giants (Uranus and Neptune). When excluding the Sun, the four giant planets account for more than 99 percent of the mass of all bodies in the Solar System.

		*Mercury	*Venus	*Earth	*Mars	°Jupiter	°Saturn	†Uranus	†Neptune
Astronomical symbol
Mean distance from Sun	km AU	57,909,175 0.38709893	108,208,930 0.72333199	149,597,890 1.00000011	227,936,640 1.52366231	778,412,010 5.20336301	1,426,725,400 9.53707032	2,870,972,200 19.19126393	4,498,252,900 30.06896348
Equatorial radius	km  :E	2,439.64 0.3825	6,051.59 0.9488	6,378.1 1	3,397.00 0.53260	71,492.68 11.209	60,267.14 9.449	25,557.25 4.007	24,766.36 3.883
Surface area	km2  :E	75,000,000 0.1471	460,000,000 0.9020	510,000,000 1	140,000,000 0.2745	64,000,000,000 125.5	44,000,000,000 86.27	8,100,000,000 15.88	7,700,000,000 15.10
Volume	km3  :E	6.083×1010 0.056	9.28×1011 0.857	1.083×1012 1	1.6318×1011 0.151	1.431×1015 1,321.3	8.27×1014 763.62	6.834×1013 63.102	6.254×1013 57.747
Mass	kg  :E	3.302×1023 0.055	4.8690×1024 0.815	5.9742×1024 1	6.4191×1023 0.107	1.8987×1027 318	5.6851×1026 95	8.6849×1025 14.5	1.0244×1026 17
Gravitational parameter	m3/s2	2.203×1013	3.249×1014	3.986×1014	4.283×1013	1.267×1017	3.793×1016	5.794×1015	6.837×1015
Density	g/cm3	5.43	5.24	5.515	3.940	1.33	0.70	1.30	1.76
Equatorial gravity	m/s2	3.70	8.87	9.81	3.71	23.12	10.44	8.69	11.00
Escape velocity	km/s	4.25	10.36	11.18	5.02	59.54	35.49	21.29	23.71
Rotation period	days	58.646225	−243.0187	0.99726968	1.02595675	0.41354	0.44401	−0.71833	0.67125
Orbital period	years	0.2408467	0.61519726	1.0000174	1.8808476	11.862615	29.447498	84.016846	164.79132
Mean orbital speed	km/s	47.8725	35.0214	29.7859	24.1309	13.0697	9.6724	6.8352	5.4778
Eccentricity		0.20563069	0.00677323	0.01671022	0.09341233	0.04839266	0.05415060	0.04716771	0.00858587
Inclination	deg.	7.00	3.39	0	1.85	1.31	2.48	0.76	1.77
Axial tilt	deg.	0.0	177.3	23.44	25.19	3.12	26.73	97.86	29.58
Mean surface temperature	K	440–100	730	287	227	152	134	76	73
Mean air temperature	K			288		165	135	76	73
Atmospheric composition		He,  Na+ P+	CO2, N2	N2, O2, Ar	CO2, N2 Ar	H2, He	H2, He	H2, He CH4	H2, He CH4
Number of known moons		0	0	1	2	67	62	27	14
Rings?		No	No	No	No	Yes	Yes	Yes	Yes
Planetary discriminant		9.1×104	1.35×106	1.7×106	1.8×105	6.25×105	1.9×105	2.9×104	2.4×104

Dwarf planets

Key
† asteroid	‡ plutoid

The IAU, the internationally recognized authority for assigning designations to celestial bodies, defines dwarf planets as bodies that are large enough to have achieved hydrostatic equilibrium, but have not cleared their neighbourhoods of similar objects. Since 2008, there have been five dwarf planets recognized by the IAU. Ceres orbits in the asteroid belt, between the orbits of Mars and Jupiter. The others orbit beyond Neptune and are subclassified as plutoids.

		†Ceres	‡Pluto	‡Haumea	‡Makemake	‡Eris
Astronomical symbol
Minor planet number		1	134340	136108	136472	136199
Mean distance from Sun	km AU	413,700,000 2.766	5,906,380,000 39.482	6,484,000,000 43.335	6,850,000,000 45.792	10,210,000,000 67.668
Mean radius	km  :E	473 0.0742	1,186 0.186	650 (960×770×495) 0.10	715±7 0.11	1,163 0.18
Volume	km3  :E	4.21×108 0.00039	6.99×109 0.0065	1.5×109 0.001	1.5×109 0.001	6.59×109 0.0061
Surface area	km2  :E	2,770,000 0.0054	17,700,000 0.035	6,800,000 0.0133	6,400,000 0.013	17,000,000 0.0333
Mass	kg  :E	9.39×1020 0.00016	1.305×1022 0.0022	4.01 ± 0.04×1021 0.0007	>2.1×1021 >0.0004	1.7×1022 0.0028
Gravitational parameter	m3/s2	6.263×1010	8.710×1011	2.674×1011	?	1.108×1012
Density	g/cm3	2.16	1.87	2.6	>1.4	2.25
Equatorial gravity	m/s2	0.27	0.62	0.63	>0.28	~0.8
Escape velocity	km/s	0.51	1.21	0.91	>0.6	1.37
Rotation period	days	0.3781	−6.38723	0.167	?	?
Orbital period	years	4.599	247.92065	285.4	309.9	557
Mean orbital speed	km/s	17.882	4.7490	4.484	4.4	3.436
Eccentricity		0.080	0.24880766	0.18874	0.159	0.44177
Inclination	deg.	10.587	17.14175	28.19	28.96	44.187
Axial tilt	deg.	4	119.59	?	?	?
Mean surface temperature	K	167	40	<50	30	30
Atmospheric composition		H2O	N2, CH4, CO	?	N2, CH4	N2, CH4
Number of known moons		0	5	2	1	1
Planetary discriminant		0.33	0.077	0.023	0.02	0.10

Most-likely additional dwarf planets

Main article: List of possible dwarf planets

These trans-Neptunian objects are theoretically large enough to be dwarf planets. Dozens more could have been included. Both Quaoar and Orcus have known moons that have allowed the mass of the systems to be determined. Both are more massive than the 5×10²⁰ kg recommendation of the IAU 2006 draft proposal as sufficient for classification as a dwarf planet.

		Orcus	Ixion	2002 MS4	Salacia	Varuna	2005 UQ513	Quaoar	2007 OR10	2007 UK126	Sedna
Minor-planet number		90482	28978	307261	120347	20000	202421	50000	225088	229762	90377
Semi-major axis	km AU	5,896,946,000 39.419	5,935,999,000 39.68	6,273,000,000 41.93	6,311,000,000 42.19	6,451,398,000 43.13	6,479,089,380 43.31	6,493,296,000 43.6	10,072,433,340 67.33	11,032,000,000 73.74	78,668,000,000 525.86
Mean radius	km  :E	473 0.0742	402 0.063	467 0.073	427 0.067	~350 0.055	460 0.072	422 0.066	~640 0.10	440 0.07	~500 0.08
Surface area	km2  :E	2,811,462 0.0055	2,030,775 0.00398	?	?	1,091,000 0.00214	2,659,044 0.0052	2,237,870 0.00439	6,157,522 0.012	2,432,849 0.005	3,000,000 0.006
Volume	km3  :E	443,273,768 0.0004	272,123,951 0.0003	?	?	549,135,785 0.0005	407,720,083 0.0004	314,793,649 0.0003	1,436,755,040 0.001	356,817,905 0.0003	500,000,000 0.0005
Mass	kg  :E	6.32×1020 0.0001	5.4×1020 0.00009	?	4.5×1020 0.000075	5.5×1020 0.00009	8.2×1020 0.0001	(1.3–1.9)×1021 0.0003	2.9×1021 0.0005	7.1×1020 0.0001	1×1021 0.00017
Density	g/cm3	1.5±0.3	2.0	?	1.16	0.9992	2.0	>2.8	2.0	2.0	2.0
Equatorial gravity	m/s2	0.27	0.22	?	0.11	0.14	0.26	0.24	<0.39	0.25	<0.5
Escape velocity	km/s	0.50	0.42	?	0.43	0.38	0.49	0.45	<0.74	0.46	<1.0
Rotation period	days	?	?	?	0.25	0.13216	?	?	?	?	0.42
Orbital period	years	247.492	249.95	271.53	274.03	283.20	285.12	287.97	552.52	633.28	12,059.06
Mean orbital speed	km/s	4.68	4.66	?	?	4.53	4.52	4.52	3.63	3.25	1.04
Eccentricity		0.22552	0.242	0.148	0.10312	0.051	0.145	0.038	0.5	0.490	0.855
Inclination	deg.	22.5	19.6	17.693	23.9396	17.2	25.69	8	30.7	23.37	11.93
Mean surface temperature	K	~42	~43	?	?	~43	~41	~41	~30	~32	~12
Number of known moons		1	0	0	1	0	0	1	0	1	0
Planetary discriminant		0.003	0.0027	<0.1	<0.1	0.0027	0.003	0.0015	<0.1	0.036	?
Absolute magnitude (H)		2.30	3.20	3.7	4.2	3.70	3.40	2.71	1.7	3.40	1.58

Satellites

Key
€ Satellite of Earth	₤ Satellite of Jupiter	$ Satellite of Saturn	₩ Satellite of Uranus	₦ Satellite of Neptune	¶ Satellite of Pluto

See also: List of natural satellites of the Solar System

There are 19 natural satellites in the Solar System that are known to be massive enough to be close to hydrostatic equilibrium, which Alan Stern calls satellite planets. However, several of these were once in equilibrium but are no longer: these include all of the moons listed for Saturn apart from Titan and Rhea. Other moons that were once in equilibrium but are no longer very round, such as Saturn's Phoebe, are not included. Satellites are listed first in order from the Sun, and second in order from their parent body.

		€Moon	₤Io	₤Europa	₤Ganymede	₤Callisto	$Mimas	$Enceladus	$Tethys	$Dione	$Rhea
Astronomical symbol
Mean distance from primary:	km	384,399	421,600	670,900	1,070,400	1,882,700	185,520	237,948	294,619	377,396	527,108
Mean radius	km  :E	1,737.1 0.272	1,815 0.285	1,569 0.246	2,634.1 0.413	2,410.3 0.378	198.30 0.031	252.1 0.04	533 0.084	561.7 0.088	764.3 0.12
Surface area	km2  :E	37,930,000 0.074	41,910,000 0.082	30,900,000 0.061	87,000,000 0.171	73,000,000 0.143	490,000 0.001	799,000 0.0016	3,570,000 0.007	3,965,000 0.0078	7,337,000 0.0144
Volume	km3  :E	2.2×1010 0.02	2.53×1010 0.02	1.59×1010 0.015	7.6×1010 0.07	5.9×1010 0.05	3.3×107 0.00003	6.7×107 0.00006	6.3×108 0.0006	7.4×108 0.0007	1.9 ×109 0.0018
Mass	kg  :E	7.3477×1022 0.0123	8.94×1022 0.015	4.80×1022 0.008	1.4819×1023 0.025	1.0758×1023 0.018	3.75×1019 0.000006	1.08×1020 0.000018	6.174×1020 0.00010	1.095×1021 0.00018	2.306×1021 0.0004
Density	g/cm3	3.3464	3.528	3.01	1.936	1.83	1.15	1.61	0.98	1.48	1.23
Equatorial gravity	m/s2	1.622	1.796	1.314	1.428	1.235	0.0636	0.111	0.145	0.231	0.264
Escape velocity	km/s	2.38	2.56	2.025	2.741	2.440	0.159	0.239	0.393	0.510	0.635
Rotation period	days	27.321582 (sync)	1.7691378 (sync)	3.551181 (sync)	7.154553 (sync)	16.68902 (sync)	0.942422 (sync)	1.370218 (sync)	1.887802 (sync)	2.736915 (sync)	4.518212 (sync)
Orbital period about primary	days	27.32158	1.769138	3.551181	7.154553	16.68902	0.942422	1.370218	1.887802	2.736915	4.518212
Mean orbital speed	km/s	1.022	17.34	13.740	10.880	8.204	14.32	12.63	11.35	10.03	8.48
Eccentricity		0.0549	0.0041	0.009	0.0013	0.0074	0.0202	0.0047	0.02	0.002	0.001
Inclination to primary's equator	deg.	18.29–28.58	0.04	0.47	1.85	0.2	1.51	0.02	1.51	0.019	0.345
Axial tilt	deg.	6.68	0	0	0–0.33	0	0	0	0	0	0
Mean surface temperature	K	220	130	102	110	134	64	75	64	87	76
Atmospheric composition		Ar, He Na, K, H	SO2	O2	O2	O2, CO2		H2O, N2 CO2, CH4
Rings?		No	No	No	No	No	No	No	No	No	Yes?

		$Titan	$Iapetus	₩Miranda	₩Ariel	₩Umbriel	₩Titania	₩Oberon	₦Triton	¶Charon
Mean distance from primary:	km	1,221,870	3,560,820	129,390	190,900	266,000	436,300	583,519	354,759	17,536
Mean radius	km  :E	2,576 0.404	735.60 0.115	235.8 0.037	578.9 0.091	584.7 0.092	788.9 0.124	761.4 0.119	1353.4 0.212	603.5 0.095
Surface area	km2  :E	83,000,000 0.163	6,700,000 0.013	700,000 0.0014	4,211,300 0.008	4,296,000 0.008	7,820,000 0.015	7,285,000 0.014	23,018,000 0.045	4,580,000 0.009
Volume	km3  :E	7.16×1010 0.066	1.67×109 0.0015	5.5×107 0.00005	8.1×108 0.0007	8.4×108 0.0008	2.06×109 0.0019	1.85×109 0.0017	1×1010 0.00923	9.2×108 0.00085
Mass	kg  :E	1.3452×1023 0.023	1.8053×1021 0.0003	6.59×1019 0.00001	1.35×1021 0.00023	1.2×1021 0.0002	3.5×1021 0.0006	3.014×1021 0.00051	2.14×1022 0.00358	1.52×1021 0.00025
Density	g/cm3	1.88	1.08	1.20	1.67	1.40	1.72	1.63	2.061	1.65
Equatorial gravity	m/s2	1.35	0.22	0.08	0.27	0.23	0.39	0.35	0.78	0.28
Escape velocity	km/s	2.64	0.57	0.19	0.56	0.52	0.77	0.73	1.46	0.58
Rotation period	days	15.945 (sync)	79.322 (sync)	1.414 (sync)	2.52 (sync)	4.144 (sync)	8.706 (sync)	13.46 (sync)	5.877 (sync)	6.387 (sync)
Orbital period about primary	days	15.945	79.322	1.4135	2.520	4.144	8.706	13.46	−5.877	6.387
Mean orbital speed	km/s	5.57	3.265	6.657	5.50898	4.66797	3.644	3.152	4.39	0.2
Eccentricity		0.0288	0.0286	0.0013	0.0012	0.005	0.0011	0.0014	0.00002	0.0022
Inclination to primary's equator	deg.	0.33	14.72	4.22	0.31	0.36	0.14	0.10	157	?
Axial tilt	deg.	0	0	0	0	0	0	0	0	?
Mean surface temperature	K	93.7	130	59	58	61	60	61	38	53
Atmospheric composition		N2, CH4							N2, CH4

Notes

Unless otherwise cited:

15. ^{^} The planetary discriminant for the planets is taken from material published by Stephen Soter. Planetary discriminants for Ceres, Pluto and Eris taken from Soter, 2006. Planetary discriminants of all other bodies calculated from the Kuiper belt mass estimate given by Lorenzo Iorio.
16. ^{^} Saturn satellite info taken from NASA Saturnian Satellite Fact Sheet.
17. ^{^} Astronomical symbols for all listed objects except Ceres taken from NASA Solar System Exploration. Symbol for Ceres was taken from material published by James L. Hilton. The Moon is the only natural satellite with an astronomical symbol, and Pluto and Ceres the only dwarf planets.
18. ^{^} Uranus satellite info taken from NASA Uranian Satellite Fact Sheet.
19. ^{^} Radii for plutoid candidates taken from material published by John Stansberry et al.
21. ^{^} Axial tilts for most satellites assumed to be zero in accordance with the Explanatory Supplement to the Astronomical Almanac: "In the absence of other information, the axis of rotation is assumed to be normal to the mean orbital plane."
22. ^{^} Natural satellite numbers taken from material published by Scott S. Sheppard.

Manual calculations (unless otherwise cited)

1. ^{^} Surface area A derived from the radius using $\begin{smallmatrix}A=4\pi r^2 \end{smallmatrix}$, assuming sphericity.
2. ^{^} Volume V derived from the radius using $\begin{smallmatrix}V=\frac{4}{3}\pi r^3 \end{smallmatrix}$, assuming sphericity.
3. ^{^} Density derived from the mass divided by the volume.
4. ^{^} Surface gravity derived from the mass m, the gravitational constant G and the radius r: G*m/r² .
5. ^{^} Escape velocity derived from the mass m, the gravitational constant G and the radius r: sqrt((2*G*m)/r) .
14. ^{^} Orbital speed is calculated using the mean orbital radius and the orbital period, assuming a circular orbit.
20. ^{^} Assuming a density of 2.0
23. ^{^} Calculated using the formula $\begin{smallmatrix}T\ =\ \frac{T_{\textrm{eff}}(1-qp_{\nu})^{1/4}}{\sqrt{2}}\sqrt{52/r},\end{smallmatrix}$ where T_eff =54.8 K at 52 AU, $p_{\nu}$ is the geometric albedo, q=0.8 is the phase integral, and $r$ is the distance from the Sun in AU. This formula is a simplified version of that in section 2.2 of Stansberry, et al., 2007, where emissivity and beaming parameter were assumed equal unity, and $\pi$ was replaced with 4 accounting for the difference between circle and sphere. All parameters mentioned above were taken from the same paper.
27. ^{^} Calculated using the formula $\begin{smallmatrix}D=\frac{1329}{\sqrt{p}}10^{-0.2H}\end{smallmatrix}$, where H is the absolute magnitude, p is the geometric albedo and D is the diameter in km, and assuming an albedo of 0.15, as per Dan Bruton.
30. ^{^} Mass derived from the density multipied by the volume.

Individual calculations

25. ^{^} Derived from density
26. ^{^} Surface area was calculated using the formula for a scalene ellipsoid:

    $\begin{smallmatrix}2\pi\left(c^2+b\sqrt{a^2-c^2}E(\alpha,m)+\frac{bc^2}{\sqrt{a^2-c^2}}F(\alpha,m)\right),\,\!\end{smallmatrix}$ where $\begin{smallmatrix}\alpha=\arccos\left(\frac{c}{a}\right)\,\,\!\end{smallmatrix}$ is the modular angle, or angular eccentricity; $\begin{smallmatrix}m=\frac{b^2-c^2}{b^2\sin(\alpha)^2}\,\!\end{smallmatrix}$ and $\begin{smallmatrix}F(\alpha,m)\,\!\end{smallmatrix}$, $\begin{smallmatrix}E(\alpha,m)\,\!\end{smallmatrix}$ are the incomplete elliptic integrals of the first and second kind, respectively. The values 980 km, 759 km, and 498 km were used for a, b, and c respectively.

Other notes

6. ^{^} Relative to Earth
7. ^{^} sidereal
8. ^{^} retrograde
9. ^{^} The inclination of the body's equator from its orbit.
10. ^{^} At pressure of 1 bar
11. ^{^} At sea level
12. ^{^} The ratio between the mass of the object and those in its immediate neighborhood. Used to distinguish between a planet and a dwarf planet.
13. ^{^} This object's rotation is synchronous with its orbital period, meaning that it only ever shows one face to its primary.
24. ^{^} Objects' planetary discriminants based on their similar orbits to Eris. Sedna's population is currently too little-known for a planetary discriminant to be determined.
28. ^{^} Proteus average diameter: 210 km; Mimas average diameter: 199 km
29. ^{^} "Unless otherwise cited" means that the information contained in the citation is applicable to an entire line or column of a chart, unless another citation specifically notes otherwise.