List of gravitationally rounded objects of the Solar System

Solar System

Objects
by orbit by size by discovery date models
Lists
Gravitationally rounded (equilibrium) objects Possible dwarf planets Moons (natural satellites) Planetary-mass moons Minor planets Comets Asteroids
Planets
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Solar System portal  Star portal
v t

This is a list of possibly gravitationally rounded objects of the Solar System, which are objects that have a rounded, ellipsoidal shape due to their own gravity (hydrostatic equilibrium). Their sizes range from planetary-mass objects like dwarf planets and some moons to the planets and the Sun. This list does not include small Solar System bodies, but it does include a sample of possible planetary-mass objects whose shapes have yet to be determined. The Sun's orbital characteristics are listed in relation to the Galactic Center, while all other objects are listed in order of their distance from the Sun.

Star[]

The Sun is a G-type main-sequence star. It contains almost 99.9% of all the mass in the Solar System.^[1]

		Sun[2][3]
Astronomical symbol[q]
Mean distance from the Galactic Center	km light years	~2.5×1017 ~26,000
Mean radius	km :E[f]	695,508 109.3
Surface area	km2 :E[f]	6.0877×1012 11,990
Volume	km3 :E[f]	1.4122×1018 1,300,000
Mass	kg :E[f]	1.9855×1030 332,978.9
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[g]	25.38
Orbital period about Galactic Center[4]	million years	225–250
Mean orbital speed[4]	km/s	~220
Axial tilt[i] to the ecliptic	deg.	7.25
Axial tilt[i] to the galactic plane	deg.	67.23
Mean surface temperature	K	5,778
Mean coronal temperature[5]	K	1–2×106
Photospheric composition		H, He, O, C, Fe, S

Planets[]

The 2006 International Astronomical Union (IAU) defines 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".^[6] 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; 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% of the mass of the Solar System.

		*Mercury[7][8][9]	*Venus[10][11][9]	*Earth[12][13][9]	*Mars[14][15][9]	°Jupiter[16][17][9]	°Saturn[18][19][9]	‡Uranus[20][21]	‡Neptune[22][23][9]
Astronomical symbol[q]
Mean distance from the 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[f]	2,440.53 0.3826	6,051.8 0.9488	6,378.1366 1	3,396.19 0.53247	71,492 11.209	60,268 9.449	25,559 4.007	24,764 3.883
Surface area	km2 :E[f]	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[f]	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[f]	3.302×1023 0.055	4.8690×1024 0.815	5.972×1024 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	5.52	3.940	1.33	0.70	1.30	1.76
Equatorial gravity	m/s2	3.70	8.87	9.8	3.71	24.79	10.44	8.87	11.15
Escape velocity	km/s	4.25	10.36	11.18	5.02	59.54	35.49	21.29	23.71
Rotation period[g]	days	58.646225	243.0187	0.99726968	1.02595675	0.41354	0.44401	0.71833	0.67125
Orbital period[g]	days years	87.969 0.2408467	224.701 0.61519726	365.256363 1.0000174	686.971 1.8808476	4,332.59 11.862615	10,759.22 29.447498	30,688.5 84.016846	60,182 164.79132
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[f]	deg.	7.00	3.39	0[12]	1.85	1.31	2.48	0.76	1.77
Axial tilt[i]	deg.	0.0	177.3[h]	23.44	25.19	3.12	26.73	97.86[h]	28.32
Mean surface temperature	K	440–100	730	287	227	152 [j]	134 [j]	76 [j]	73 [j]
Mean air temperature[k]	K			288		165	135	76	73
Atmospheric composition		He,  Na+ K+	CO2, N2, SO2	N2, O2, Ar, CO2	CO2, N2 Ar	H2, He	H2, He	H2, He CH4	H2, He CH4
Number of known moons[v]		0	0	1	2	79	82	27	14
Rings?		No	No	No	No	Yes	Yes	Yes	Yes
Planetary discriminant[l][o]		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[]

Dwarf planets are bodies that are massive and warm 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, though of these only Ceres, which orbits in the asteroid belt between the orbits of Mars and Jupiter, has been confirmed.^[ae] The others all orbit beyond Neptune.

		†Ceres[24]	‡Pluto[25][26]	‡Haumea[27][28][29]	‡Makemake[30][31]	‡Eris[32]
Astronomical symbol[q]
Minor planet number		1	134340	136108	136472	136199
Mean distance from the 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[f]	473 0.0742	1,188.3[9] 0.186	816 (2100 × 1680 × 1074) 0.13[33][34]	715 0.11[35]	1,163 0.18[36]
Volume	km3 :E[f]	4.21×108 0.00039[b]	6.99×109 0.0065	1.98×109 0.0018	1.7×109 0.0016[b]	6.59×109 0.0061[b]
Surface area	km2 :E[f]	2,770,000 0.0054[a]	17,700,000 0.035	8,140,000 0.016[z]	6,900,000 0.0135[a]	17,000,000 0.0333[a]
Mass	kg :E[f]	9.39×1020 0.00016	1.30×1022 0.0022	4.01 ± 0.04×1021 0.0007[37]	< 4.4 ×1021 < 0.0007	1.65×1022 0.0028
Gravitational parameter	m3/s2	6.263 × 1010	8.710 × 1011	2.674 × 1011	< 2.937 × 1011	1.108 × 1012
Density	g/cm3	2.16	1.87	2.02[33]	2.10	2.43
Equatorial gravity	m/s2	0.27[d]	0.62	0.63[d]	< 0.57	0.82[d]
Escape velocity	km/s[e]	0.51	1.21	0.91	< 0.91	1.37
Rotation period[g]	days	0.3781	6.3872	0.1631	0.9511	14.560
Orbital period[g]	years	4.599	247.9	283.8	306.2	559
Mean orbital speed	km/s	17.882	4.75	4.48[o]	4.40[o]	3.44[n]
Eccentricity		0.080	0.249	0.195	0.161	0.436
Inclination[f]	deg.	10.59	17.14	28.21	28.98	44.04
Axial tilt[i]	deg.	4	119.6[h]	≈126	?	≈78
Mean surface temperature[w]	K	167[38]	40[39]	<50[40]	30	30
Atmospheric composition		H2O	N2, CH4, CO	?	N2, CH4[41]	N2, CH4[42]
Number of known moons[v]		0	5	2[43]	1[44]	1[45]
Planetary discriminant[l][o]		0.33	0.077	0.023	0.02	0.10

Astronomers generally agree that several other trans-Neptunian objects may be large enough to be dwarf planets, given current uncertainties. However, there has been disagreement on the required size. Early speculations were based on the small moons of the giant planets, which attain roundness around a 400 km threshold.^[46] However, these moons are at higher temperatures than TNOs and are icier than TNOs are likely to be.

Many TNOs in the 400–1000 km size range are dark and low-density bodies, like 174567 Varda, 229762 Gǃkúnǁʼhòmdímà, or (55637) 2002 UX25. They appear to retain internal porosity from their formation, which is possible because water ice is strong enough at Kuiper belt temperatures to support open spaces in objects this size. This would mean that they are not planetary bodies. Their dark surfaces indicate that they have never been resurfaced, and thus that they have at most incompletely differentiated (and might not have differentiated at all). If this assessment is correct, then only the largest few TNOs could be dwarf planets.^[47]

Quaoar, Orcus, and Gonggong have moons that have allowed their mass and density to be determined using Kepler's third law, and they are either bright enough to suggest resurfacing and thus planetary geology at least at some point in their past, or are dense enough that they are clearly solid bodies and thus at least potentially dwarf planets. Sedna and Salacia have been included as two of the stronger remaining candidates: Sedna is bright but has unknown density, while Salacia is dark but is dense enough to be solid.

		Orcus[48]	Salacia[49]	Quaoar[50]	Gonggong[51]	Sedna[52]
Minor-planet number		90482	120347	50000	225088	90377
Semi-major axis	km AU	5,896,946,000 39.419	6,310,600,000 42.18	6,535,930,000 43.69	10,072,433,340 67.33	78,668,000,000 525.86
Mean radius[s]	km :E[f]	458.5[53] 0.0720	423[54] 0.0664	560.5[55] 0.0870	615[56] 0.0982	497.5[57] 0.0780
Surface area[a]	km2 :E[f]	2,641,700 0.005179	2,248,500 0.004408	3,948,000 0.007741	4,932,300 0.009671	3,110,200 0.006098
Volume[b]	km3 :E[f]	403,744,500 0.000373	317,036,800 0.000396	737,591,000 0.000681	1,030,034,600 0.000951	515,784,000 0.000476
Mass[t]	kg :E[f]	6.32×1020[58] 0.0001	4.9×1020[54] 0.0001	1.41×1021[59] 0.0003	1.75×1021[56] 0.0003	?
Density[t]	g/cm3	1.5±0.3[58]	1.50±0.12[54]	1.99±0.46[59]	1.74±0.16	?
Equatorial gravity[d]	m/s2	0.27	0.18	0.24	0.285	?
Escape velocity[e]	km/s	0.50	0.39	0.45	0.604	?
Rotation period[g]	days	?	?	0.3683	0.9333	0.4280[60]
Orbital period[g]	years	247.49	273.98	287.97	552.52	12,059
Mean orbital speed	km/s	4.68	4.57	4.52	3.63	1.04
Eccentricity		0.226	0.106	0.038	0.506	0.855
Inclination[f]	deg.	20.59	23.92	7.99	30.74	11.93
Mean surface temperature[w]	K	~42	~43	~41	~30	~12
Number of known moons		1[61]	1	1[62]	1	0
Planetary discriminant[l][o]		0.003	<0.1	0.0015	<0.1	?[x]
Absolute magnitude (H)		2.3	4.1	2.71	1.8	1.5

Satellites[]