List of gravitationally rounded objects of the Solar System

Objects in the Solar System
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Categories
Round objects Moons Minor planets
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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.^[1] 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 classified as dwarf planets, and the remainder are termed small Solar System bodies. In addition, the Sun itself and 19 known natural satellites are also massive enough to have achieved hydrostatic equilibrium.^[2] All known objects in the Solar System with a hydrostatic shape are listed below, 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.^[3]

		Sun[4]
Astronomical symbol[q]
Mean distance from Galactic Center	km light years	~2.5×1017 ~26,000
Mean radius	km  :E[f]	696,000 109
Surface area	km2  :E[f]	6.0877×1012 11,990
Volume	km3  :E[f]	1.4122×1018 1,300,000
Mass	kg  :E[f]	1.9891×1030 332,946
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[5]	million years	225–250
Mean orbital speed[5]	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[6]	K	1–2×106
Photospheric composition		H, He, O, C, Fe, S

Planets

Key
* terrestrial planet	° gas giant

Planets both are large enough to have achieved hydrostatic equilibrium and have cleared their neighborhoods of similar objects. There are four terrestrial planets and four gas giants in the Solar System. The latter combined comprise more than 99 percent of the mass in the Solar System excluding that of the Sun.

		*Mercury[7]	*Venus[8]	*Earth[9]	*Mars[10]	°Jupiter[11]	°Saturn[12]	°Uranus[13]	°Neptune[14]
Astronomical symbol[q]
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[f]	2,439.64 0.3825	6,051.59 0.9488	6,378.1 1	3,397.00 0.53226	71,492.68 11.209	60,267.14 9.449	25,557.25 4.007	24,766.36 3.883
Surface area	km²  :E[f]	75,000,000 0.1471	460,000,000 0.9010	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 0.87	1.083×1012 1	1.6318×1011 0.151	1.431×1015 1,321.3	8.27×1014 763.59	6.834×1013 63.086	6.254×1013 57.74
Mass	kg  :E[f]	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	1.0244×1026 17
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[g]	days	58.646225	−243.0187[h]	0.99726968	1.02595675	0.41354	0.44401	−0.71833[h]	0.67125
Orbital period[g]	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[f]	deg.	7.00	3.39	0[9]	1.85	1.31	2.48	0.76	1.77
Axial tilt[i]	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 [j]	134 [j]	76 [j]	72 [j]
Mean air temperature[k]	K			288		165	135	76	73
Atmospheric composition		He  Na+  P+	CO2  N2	N2  O2	CO2  N2  Ar	H2  He	H2  He	H2  He  CH4	H2  He  CH4
Number of known moons[v]		0	0	1	2	64	62	27	13
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

Key
† Ceres	‡ plutoid

Dwarf planets are large enough to have achieved hydrostatic equilibrium, but have not cleared their neighbourhoods of similar objects. There are currently five objects in this category. Ceres lies in the asteroid belt, between the orbits of Mars and Jupiter. The others lie beyond Neptune's orbit and are sub-classified as plutoids. The IAU has recognised these objects as dwarf planets:

		†Ceres[15]	‡Pluto[16]	‡Haumea[17]	‡Makemake[18]	‡Eris[19]
Astronomical symbol[q]
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[f]	471 0.0738	1,148.07 0.180	575 0.1537[20]	750+200 −100 0.12[20]	1,200 0.19[20]
Volume	km3  :E[f]	4.37×108 0.0005[b]	6.33×109 0.007	1.3–1.6×109 0.001[y]	1.8×109 0.002[b]	7.23×109 0.008[b]
Surface area	km²  :E[f]	2,800,000 0.0055[a]	17,000,000 0.0333	6,800,000 0.0133[z]	7,000,000 0.015[a]	18,000,000 0.0353[a]
Mass	kg  :E[f]	9.5×1020 0.00016	1.3×1022 0.0022	4.2 ± 0.1×1021 0.0007[21]	4×1021 0.0007	1.7×1022 0.0028[22]
Density	g/cm3	2.08	2.0	2.6–3.3[23]	2.0[c]	2.25[c]
Equatorial gravity	m/s2	0.27[d]	0.60	0.44[d]	0.5[d]	~0.8[d]
Escape velocity	km/s[e]	0.51	1.23	0.84	0.8	1.37
Rotation period[g]	days	0.3781	−6.38718[h]	0.167	?	?
Orbital period[g]	years	4.599	247.92065	285.4	309.9	557
Mean orbital speed	km/s	17.882	4.7490	4.484[o]	4.4[o]	3.436[n]
Eccentricity		0.080	0.24880766	0.18874	0.159	0.44177
Inclination[f]	deg.	10.587	17.14175	28.19	28.96	44.187
Axial tilt[i]	deg.	4	119.61	?	?	?
Mean surface temperature[w]	K	167[24]	40[25]	<50[26]	30	30
Atmospheric composition		H2O, O2	N2, CH4		N2, CH4.[27]	N2, CH4[28]
Number of known moons[v]		0	4	2[29]	0[30]	1[31]
Planetary discriminant[l][o]		0.33	0.077	0.023	0.02	0.10

Round satellites

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

See also: List of moons

There are 19 natural satellites in the Solar System massive enough to have achieved hydrostatic equilibrium. Another satellite, the Neptunian moon Proteus, is not in hydrostatic equilibrium, but is slightly larger than Mimas, the smallest of the 19 rounded moons.^[ab] Satellites are listed first in order from the Sun, and second in order from their parent body.

		€Moon[32]	₤Io[33]	₤Europa[34]	₤Ganymede[35]	₤Callisto[36]	$Mimas[p]	$Enceladus[p]	$Tethys[p]	$Dione[p]	$Rhea[p]
Astronomical symbol[q]
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[f]	1,737.1 0.273	1,815 0.286	1,569 0.245	2,634.1 0.413	2,410.3 0.378	198.30 0.031	252.1 0.04	533 0.083	561.7 0.088	764.3 0.12
Surface area[a]	km²  :E[f]	37,930,000 0.074	41,910,000 0.082	30,900,000 0.061	87,000,000 0.143	73,000,000 0.143	490,000 0.001	799,000 0.0016	4,940,000 0.01	3,965,000 0.0078	7,337,000 0.0144
Volume[b]	km3  :E[f]	2.2×1010 0.02	2.53×1010 0.02	1.59×1010 0.07	7.6×1010 0.15	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 0.0017
Mass	kg  :E[f]	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 0.00132	1.095×1021 0.0003	2.306×1021 0.0004
Density[c]	g/cm3	3.3464	3.528	3.01	1.936	1.83	1.15	1.61	0.98	1.48	1.23
Equatorial gravity[d]	m/s2	1.622	1.796	1.314	1.428	1.235	0.0636	0.111	0.145	0.231	0.264
Escape velocity[e]	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[g]	27.321582 (sync)[m]	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[g]	27.32158	1.769138	3.551181	7.154553	16.68902	0.942422	1.370218	1.887802	2.736915	4.518212
Mean orbital speed[o]	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[i][u]	deg.	6.68	0	0	0–0.33[37]	0	0	0	0	0	0
Mean surface temperature[w]	K	220	130	102	110[38]	134	64	75	64	87	76
Atmospheric composition		H  He Na+  K+ Ar	SO2[39]	O2[40]	O2[41]	O2  CO2[42]		H2O, N2, CO2, CH4[43]
Rings?		No	No	No	No	No	No	No	No	No	Yes?

		$Titan[p]	$Iapetus[p]	₩Miranda[r]	₩Ariel[r]	₩Umbriel[r]	₩Titania[r]	₩Oberon[r]	₦Triton[44]	¶Charon[16]
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[f]	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[a]	km²  :E[f]	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[b]	km3  :E[f]	7.16×1010 0.066	1.67×109 0.0015	5.5×107 0.00005	8.1×108 0.0008	8.4×108 0.0008	2.06×109 0.0019	1.85×109 0.0017	1×1010 0.00958	9.2×108 0.00085
Mass	kg  :E[f]	1.3452×1023 0.023	1.8053×1021 0.0003	6.59×1019 0.00001	1.35×1021 0.00022	1.2×1021 0.0002	3.5×1021 0.0006	3.014×1021 0.00046	2.14×1022 0.00358	1.52×1021 0.00025
Density[c]	g/cm3	1.88	1.08	1.20	1.67	1.40	1.72	1.63	2.061	1.65
Equatorial gravity[d]	m/s2	1.35	0.22	0.08	0.27	0.23	0.39	0.35	0.78	0.28
Escape velocity[e]	km/s	2.64	0.57	0.19	0.56	0.52	0.77	0.73	1.46	0.58
Rotation period	days[g]	15.945 (sync)[m]	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[h]	6.387
Mean orbital speed[o]	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	0.34854	15.47	4.2	0.26	0.36	0.34	157	?
Axial tilt[i][u]	deg.	0	0	0	0	0	0	0	0	?
Mean surface temperature[w]	K	93.7[45]	130	59	58	61	60	61	38 [46]	53
Atmospheric composition		N2, CH4[47]							N2, CH4[48]

Largest dwarf-planet candidates

See also: Small Solar System body and List of dwarf planet candidates

These trans-Neptunian objects are theoretically large enough to be given dwarf-planet status in the future. A further 30 or so TNOs could eventually be included,^[2] and perhaps three other asteroids.^[49] Both Quaoar and Orcus have known moons that have allowed the mass of the systems to be calculated. Both candidates are more massive than the 5×10²⁰ kg recommendation of the IAU 2006 draft proposal.^[50]

		Orcus[51]	Ixion[52]	Varuna[53]	2005 UQ513[54]	Quaoar[55]	2002 TC302[56]	2007 OR10[57]	2007 UK126[58]	2005 QU182[59]	Sedna[60]
Minor-planet number		90482	28978	20000	202421	50000	84522	225088	229762		90377
Semi-major axis	km AU	5,896,946,000 39.419	5,935,999,000 39.68	6,451,398,000 43.13	6,479,089,380 43.31	6,493,296,000 43.6	8,264,380,000 55.24	10,072,433,340 67.33	11,032,000,000 73.74	16,991,749,800 113.58	78,668,000,000 525.86
Mean radius[s]	km  :E[f]	473 0.0742	402 0.063	508 0.08	460 0.072[aa]	422 0.066	600 0.094	<700 0.11[aa]	440 0.07[aa]	525 0.08[aa]	<950 0.149
Surface area[a]	km²  :E[f]	2,811,462 0.0055	2,030,775 0.00398	1,091,000 0.00636	2,659,044 0.0052	2,237,870 0.00439	4,521,600 0.00887	6,157,522 0.012	2,432,849 0.005	3,463,606 0.007	11,341,150 0.0222
Volume[b]	km3  :E[f]	443,273,768 0.0004	272,123,951 0.0002	549,135,785 0.0005	407,720,083 0.0003	314,793,649 0.0002	904,320,000 0.0008	1,436,755,040 0.001	356,817,905 0.0002	606,131,033 0.0004	3,591,364,000 0.0033
Mass[t]	kg  :E[f]	6.32×1020[61] 0.0001	5.4×1020 0.00009	5.5×1020 0.00009	8.2×1020 0.0001	(2.1–2.9)×1021[62] 0.0004	1.8×1021 0.0003	2.9×1021 0.0005	7.1×1020 0.0001	1.2×1021 0.0002	7.2×1021 0.0012
Density[t]	g/cm3	1.5±0.3[61]	2.0	0.9992[63]	2.0	>2.8[62]	2.0	2.0	2.0	2.0	2.0
Equatorial gravity[d]	m/s2	0.27	0.22	0.14	0.26	0.24	0.34	<0.39	0.25	0.29	<0.5
Escape velocity[e]	km/s	0.50	0.42	0.38	0.49	0.45	0.63	<0.74	0.46	0.55	<1.0
Rotation period[g]	days	?	?	0.13216[63]	?	?	?	?	?	?	0.42[64]
Orbital period[g]	years	247.492	249.95	283.20	285.12	287.97	410.62	552.52	633.28	1,210.53	12,059.06
Mean orbital speed	km/s	4.68	4.66	4.53	4.52	4.52	3.93	3.63	3.25	2.79	1.04
Eccentricity		0.22552	0.242	0.051	0.145	0.038	0.292	0.5	0.490	0.675	0.855
Inclination[f]	deg.	22.5	19.6	17.2	25.69	8	35	30.7	23.37	14.03	11.93
Mean surface temperature[w]	K	~42	~43	~43	~41	~41	~38	~30	~32	~25	~12
Number of known moons		1[65]	0	0	0	1[66]	0	0	0	0	0
Planetary discriminant[l][o]		0.003	0.0027	0.0027	0.003	0.0015	0.335	0.18[x]	0.036[x]	0.007[x]	?[x]
Absolute magnitude (H)		2.30	3.20	3.70	3.40	2.71	3.8	1.7	3.40	3.40	1.58

See also

Notes

Unless otherwise cited:^[ac]

15. ^{^} The planetary discriminant for the planets is taken from material published by Stephen Soter.^[67] 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.^[68]
16. ^{^} Saturn satellite info taken from NASA Saturnian Satellite Fact Sheet.^[69]
17. ^{^} Astronomical symbols for all listed objects except Ceres taken from NASA Solar System Exploration.^[70] Symbol for Ceres was taken from material published by James L. Hilton.^[71] 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.^[72]
19. ^{^} Radii for plutoid candidates taken from material published by John Stansberry et al.^[20]
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."^[73]
22. ^{^} Natural satellite numbers taken from material published by Scott S. Sheppard.^[74]

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 Pluto's 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_ν is the geometrical 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,^[20] where emissivity and beaming parameter were assumed equal unity, and π 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.^[75]

Individual calculations

25. ^{^} Derived from density
26. ^{^} Surface area was calculated using the formula for an 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;^[44] Mimas average diameter: 199 km^[69]
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.

References

1. ^ "IAU 2006 General Assembly: Result of the IAU Resolution votes" (Press release). International Astronomical Union (News Release – IAU0603). 2006-08-24. http://www.iau.org/public_press/news/release/iau0603/. Retrieved 2007-12-31.  (orig link)
2. ^ ^{a b} Mike Brown. "The Dwarf Planets". CalTech. http://www.gps.caltech.edu/~mbrown/dwarfplanets/. Retrieved 2008-09-25. 
3. ^ M Woolfson (2000). "The origin and evolution of the solar system". Astronomy & Geophysics 41 (1): 1.12. doi:10.1046/j.1468-4004.2000.00012.x. 
4. ^ NASA Solar System exploration Sun factsheet and NASA Sun factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
5. ^ ^{a b} Stacy Leong (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". In Glenn Elert (ed.). The Physics Factbook (self-published). http://hypertextbook.com/facts/2002/StacyLeong.shtml. Retrieved 2008-06-26. 
6. ^ Markus J. Aschwanden (2007). "The Sun". In Lucy Ann McFadden, Paul R. Weissman, Torrence V. Johnsson. Encyclopedia of the Solar System. Academic Press. p. 80. 
7. ^ NASA Mercury Fact Sheet and NASA Solar System Exploration Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
8. ^ NASA Venus Factsheet and NASA Solar System Exploration Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
9. ^ ^{a b} NASA Earth factsheet and NASA Solar System Exploration Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
10. ^ NASA Mars Factsheet and NASA Mars Solar System Exploration Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
11. ^ NASA Jupiter factsheet and NASA Solar System Exploration Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
12. ^ NASA Saturn factsheet and NASA Solar System Exploration Saturn Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
13. ^ NASA Uranus factsheet and NASA Solar System Exploration Uranus Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
14. ^ NASA Neptune factsheet and NASA Solar System Exploration Neptune Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
15. ^ "NASA Asteroid Factsheet". NASA. http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact.html. Retrieved 2008-11-17. 
16. ^ ^{a b} NASA Pluto factsheet and NASA Solar System Exploration Pluto Factsheet Retrieved on 2008-11-17 (unless otherwise cited)
17. ^ (i)D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". The Astrophysical Journal 639 (2): 1238–1251. arXiv:astro-ph/0509401. Bibcode 2006ApJ...639.1238R. doi:10.1086/499575. 
    (ii)"Jet Propulsion Laboratory Small-Body Database Browser: 136108 Haumea". NASA's Jet Propulsion Laboratory (2008-05-10 last obs). http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=136108. Retrieved 2008-11-13.  (unless otherwise cited)
18. ^ (i)Marc W. Buie (2008-04-05). "Orbit Fit and Astrometric record for 136472". SwRI (Space Science Department). http://www.boulder.swri.edu/~buie/kbo/astrom/136472.html. Retrieved 2008-07-13. 
    (ii)"NASA Small Bodies Database Browser: 136472 Makemake (2005 FY9)". NASA JPL. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=136472. Retrieved 2008-10-03.  (unless otherwise cited)
19. ^ "NASA Small Body Database Browser: Eris". NASA JPL. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Eris. Retrieved 2008-11-13.  (unless otherwise cited)
20. ^ ^{a b c d e} J. Stansberry, W. Grundy, M. Brown, et al. (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". The Solar System beyond Neptune (University of Arizona Press). arXiv:astro-ph/0702538. Bibcode 2008ssbn.book..161S. 
21. ^ M. E. Brown, A. H. Bouchez, D. L. Rabinowitz, R. Sari, C. A. Trujillo, M. A. van Dam, R. Campbell, J. Chin, S. Hartman, E. Johansson, R. Lafon, D. LeMignant, P. Stomski, D. Summers, P. L. Wizinowich (October 2005). "Keck Observatory laser guide star adaptive optics discovery and characterization of a satellite to large Kuiper belt object 2003 EL61". The Astrophysical Journal Letters 632 (L45): L45. Bibcode 2005ApJ...632L..45B. doi:10.1086/497641. 
22. ^ Michael E. Brown and Emily L. Schaller (2007). "The Mass of Dwarf Planet Eris". Science 316 (1585): 1585. Bibcode 2007Sci...316.1585B. doi:10.1126/science.1139415. PMID 17569855. http://www.sciencemag.org/cgi/content/abstract/316/5831/1585. 
23. ^ D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL₆₁, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". The Astrophysical Journal 639 (2): 1238–1251. arXiv:astro-ph/0509401. Bibcode 2006ApJ...639.1238R. doi:10.1086/499575. 
24. ^ O. Saint-Pé; N. Combes, F. Rigaut (1993). "Ceres surface properties by high-resolution imaging from Earth". Icarus 105 (2): 271–281. Bibcode 1993Icar..105..271S. doi:10.1006/icar.1993.1125. 
25. ^ T. Ker (2006). "Astronomers: Pluto colder than expected". Space.com (via CNN.com). http://www.cnn.com/2006/TECH/space/01/03/pluto.temp/index.html.  Retrieved on 2006-03-05.
26. ^ Chadwick A. Trujillo, Michael E. Brown, Kristina Barkume, Emily Shaller, David L. Rabinowitz (February 2007). "The Surface of 2003 EL61 in the Near Infrared". The Astrophysical Journal 655 (2): 1172–1178. arXiv:astro-ph/0601618. Bibcode 2007ApJ...655.1172T. doi:10.1086/509861. 
27. ^ Mike Brown, K. M. Barksume, G. L. Blake, E. L. Schaller, D. L. Rabinowitz, H. G. Roe and C. A. Trujillo (2007). "Methane and Ethane on the Bright Kuiper Belt Object 2005 FY₉". The Astronomical Journal 133 (1): 284–289. Bibcode 2007AJ....133..284B. doi:10.1086/509734. 
28. ^ J. Licandro, W. M. Grundy, N. Pinilla-Alonso, P. Leisy (2006). "Visible spectroscopy of 2003 UB₃₁₃: evidence for N₂ ice on the surface of the largest TNO" (PDF). Astronomy and Astrophysics 458 (1): L5–L8. arXiv:astro-ph/0608044. Bibcode 2006A&A...458L...5L. doi:10.1051/0004-6361:20066028. http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/pdf/2006/40/aa6028-06.pdf. 
29. ^ D. Ragozzine, M. E. Brown, C. A. Trujillo, E. L. Schaller. "Orbits and Masses of the 2003 EL61 Satellite System". AAS DPS conference 2008. http://www.abstractsonline.com/viewer/viewAbstract.asp?CKey={421E1C09-F75A-4ED0-916C-8C0DDB81754D}&MKey={35A8F7D5-A145-4C52-8514-0B0340308E94}&AKey={AAF9AABA-B0FF-4235-8AEC-74F22FC76386}&SKey={545CAD5F-068B-4FFC-A6E2-1F2A0C6ED978}. Retrieved 2008-10-17. 
30. ^ Brown, M. E. et al. (2006). "Satellites of the Largest Kuiper Belt Objects" (PDF). The Astrophysical Journal 639: L43. arXiv:astro-ph/0510029. Bibcode 2006ApJ...639L..43B. doi:10.1086/501524. http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf. Retrieved 2011-10-19.  edit
31. ^ M. E. Brown, M. A. van Dam, A. H. Bouchez, D. LeMignant, C. A. Trujillo, R. Campbell, J. Chin, Conrad A., S. Hartman, E. Johansson, R. Lafon, D. L. Rabinowitz, P. Stomski, D. Summers, P. L. Wizinowich (2006). "Satellites of the largest Kuiper belt objects". The Astrophysical Journal 639 (1): L43–L46. arXiv:astro-ph/0510029. Bibcode 2006ApJ...639L..43B. doi:10.1086/501524. 
32. ^ NASA Moon factsheet and NASA Solar System Exploration Moon Factsheet NASA Retrieved on 2008-11-17 (unless otherwise cited)
33. ^ "NASA Io Factsheet". NASA. http://www2.jpl.nasa.gov/galileo/io/fact.html#stats. Retrieved 2008-11-16.  (unless otherwise cited)
34. ^ "NASA Europa Factsheet". NASA. http://www2.jpl.nasa.gov/galileo/europa/. Retrieved 2008-11-16.  (unless otherwise cited)
35. ^ "NASA Ganymede Factsheet". NASA. http://www2.jpl.nasa.gov/galileo/ganymede/fact.html. Retrieved 2008-11-16.  (unless otherwise cited)
36. ^ "NASA Callisto Factsheet". NASA. http://www2.jpl.nasa.gov/galileo/callisto/. Retrieved 2008-11-16.  (unless otherwise cited)
37. ^ Bruce G. Bills (2005). "Free and forced obliquities of the Galilean satellites of Jupiter". Icarus 175 (1): 233–247. Bibcode 2005Icar..175..233B. doi:10.1016/j.icarus.2004.10.028. 
38. ^ GS Orton; G.R. Spencer, L.D. Travis, et al. (1996). "Galileo Photopolarimeter-radiometer observations of Jupiter and the Galilean Satellites". Science 274 (5286): 389–391. Bibcode 1996Sci...274..389O. doi:10.1126/science.274.5286.389. 
39. ^ JC Pearl, et al. (1979). "Identification of gaseous SO2 and new upper limits for other gases on Io". Nature 288 (5725): 755. Bibcode 1979Natur.280..755P. doi:10.1038/280755a0. 
40. ^ D.T. Hall et al.; Detection of an oxygen atmosphere on Jupiter's moon Europa, Nature, Vol. 373 1995, 677–679 (accessed 2006-15-04)
41. ^ DT Hall, PD Feldman, MA McGrath, et al. (1998). "The Far-Ultraviolet Oxygen Airglow of Europa and Ganymede". The Astrophysical Journal 499 (1): 475–481. Bibcode 1998ApJ...499..475H. doi:10.1086/305604.  Retrieved on 2008-11-17.
42. ^ Liang, Mao-Chang (2005). "Atmosphere of Callisto" (PDF). Journal of Geophysics Research 110 (E02003): E02003. Bibcode 2005JGRE..11002003L. doi:10.1029/2004JE002322. http://yly-mac.gps.caltech.edu/ReprintsYLY/N164Liang_Callisto%2005/Liang_callisto_05.pdf.  Retrieved on 2008-11-17.
43. ^ JH Waite, et al. (2006). "Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure". Science 311 (5766): 1419–1422. Bibcode 2006Sci...311.1419W. doi:10.1126/science.1121290. PMID 16527970.  Retrieved on 2008-11-17.
44. ^ ^{a b} Triton info taken from NASA Neptunian Satellite Fact Sheet NASA Retrieved on 2009-01-18 (unless otherwise cited)
45. ^ C. A. Hasenkopf (2007). "Optical Properties of Titan Haze Laboratory Analogs Using Cavity Ring Down Spectroscopy". Workshop on Planetary Atmospheres. http://64.233.183.104/search?q=cache:H1UhAFtLEpEJ:www.lpi.usra.edu/meetings/patm2007/pdf/9034.pdf+titan+anti-greenhouse-effect+2006+OR+2007&hl=en&ct=clnk&cd=3&gl=uk. Retrieved 2007-10-16. 
46. ^ Kimberly Tryka, Robert Brown, V. Anicich et al. (August 1993). "Spectroscopic Determination of the Phase Composition and Temperature of Nitrogen Ice on Triton". Science 261 (5122): 751–754. Bibcode 1993Sci...261..751T. doi:10.1126/science.261.5122.751. PMID 17757214. 
47. ^ H. B. Niemann, et al. (2005). "The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe". Nature 438 (7069): 779–784. Bibcode 2005Natur.438..779N. doi:10.1038/nature04122. PMID 16319830. 
48. ^ A L Broadfoot, S K Bertaux, J E Dessler et al. (1989-12-15). "Ultraviolet Spectrometer Observations of Neptune and Triton". Science 246 (4936): 1459–1466. Bibcode 1989Sci...246.1459B. doi:10.1126/science.246.4936.1459. PMID 17756000. 
49. ^ Ron Ekers. "IAU Planet Definition Committee". International Astronomical Union. http://www.iau.org/public_press/news/release/iau0601/newspaper/. Retrieved 2008-10-13. 
50. ^ O. Gingerich (2006). "The Path to Defining Planets" (PDF). Harvard-Smithsonian Center for Astrophysics and IAU EC Planet Definition Committee chair. http://astro.cas.cz/nuncius/nsiii_03.pdf. Retrieved 2007-03-13. 
51. ^ "JPL Small-Body Database Browser: 90482 Orcus (2004 DW)". NASA JPL. 2008-02-10 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Orcus. Retrieved 2008-07-02.  (unless otherwise cited)
52. ^ "JPL Small-Body Database Browser: 28978 Ixion (2001 KX76)". NASA JPL. 2007-07-12 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Ixion. Retrieved 2008-10-04.  (unless otherwise cited)
53. ^ "JPL Small-Body Database Browser: 20000 Varuna (2000 WR106)". NASA JPL. 2007-11-17 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=20000. Retrieved 2008-07-02.  (unless otherwise cited)
54. ^ "JPL Small-Body Database Browser: (2005 UQ513)". 2008-11-29 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2005UQ513. Retrieved 2008-07-31. (unless otherwise cited)
55. ^ "NASA JPL Database Browser: 50000 Quaoar". NASA JPL. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=50000. Retrieved 2008-12-19.  (unless otherwise cited)
56. ^ "JPL Small-Body Database Browser: 84522 (2002 TC302)". 2007-12-08 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=84522. Retrieved 2009-03-05.  (unless otherwise cited)
57. ^ "NASA Small Bodies Database Browser: 2007 OR10". NASA JPL. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007OR10. Retrieved 2008-12-20.  (unless otherwise cited)
58. ^ "JPL Small-Body Database Browser: 229762 (2007 UK126)". 2009-12-20 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=229762. Retrieved 2010-05-02.  (unless otherwise cited)
59. ^ "JPL Small-Body Database Browser: (2005 QU182)". 2008-10-24 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2005QU182. Retrieved 2008-12-09.  (unless otherwise cited)
60. ^ Marc W. Buie (2007-08-13). "Orbit Fit and Astrometric record for 90377". Deep Ecliptic Survey. http://www.boulder.swri.edu/~buie/kbo/astrom/90377.html. Retrieved 2006-01-17.  (unless otherwise cited)
61. ^ ^{a b} Brown, M.E.; Ragozzine, D.; Stansberry, J.; Fraser, W.C. (2009). "The size, density, and formation of the Orcus-Vanth system in the Kuiper belt". AJ. arXiv:0910.4784. Bibcode 2010AJ....139.2700B. doi:10.1088/0004-6256/139/6/2700. 
62. ^ ^{a b} Brown, M.E.; Fraser, Wesley (2009). "Quaoar: A Rock in the Kuiper Belt". DPS meeting #41. American Astronomical Society. Bibcode 2009DPS....41.6503F.  (Backup reference)
63. ^ ^{a b} David C. Jewitt and Scott S. Sheppard (2002). "Physical Properties of Trans-Neptunian Object (20000) Varuna". The Astronomical Journal 123 (4): 2110–2120. arXiv:astro-ph/0201082. Bibcode 2002AJ....123.2110J. doi:10.1086/339557. http://www.iop.org/EJ/article/1538-3881/123/4/2110/201498.html.  Retrieved on 2008-12-19.
64. ^ "Case of Sedna's Missing Moon Solved". Harvard Smithsonian Center for Astrophysics. 2005. http://www.cfa.harvard.edu/news/2005/pr200510.html. Retrieved 2011-07-05. 
65. ^ Distant EKO The Kuiper Belt Electronic newsletter, March 2007 Retrieved on 2008-11-17
66. ^ "IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637),, (90482); V1281 Sco; V1280 Sco". International Astronomical Union. http://www.cbat.eps.harvard.edu/iauc/08800/08812.html. Retrieved 2011-07-05. 
67. ^ Stephen Soter (2006-08-16). "What is a Planet?". The Astronomical Journal 132 (6): 2513–2519. arXiv:astro-ph/0608359. Bibcode 2006AJ....132.2513S. doi:10.1086/508861. 
68. ^ Lorenzo Iorio (2007-03). "Dynamical determination of the mass of the Kuiper Belt from motions of the inner planets of the Solar system". Monthly Notices of the Royal Astronomical Society 375 (4): 1311–1314. Bibcode 2007MNRAS.tmp...24I. doi:10.1111/j.1365-2966.2006.11384.x. 
69. ^ ^{a b} NASA Saturnian Satellite Fact Sheet NASA Retrieved on 2008-11-17
70. ^ "NASA Solar System Exploration: Planet Symbols". NASA. http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=167. Retrieved 2009-01-26. 
71. ^ James L. Hilton. "When did asteroids become minor planets?" (PDF). U.S. Naval Observatory. http://sd-www.jhuapl.edu/weaver_projects/GPD/Contributed_Talks/hilton_gpd_poster.pdf. Retrieved 2008-10-25. 
72. ^ "NASA Uranian Satellite Fact Sheet". NASA. http://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html. Retrieved 2008-11-17. 
73. ^ P. Kenneth Seidelmann, ed (1992). Explanatory Supplement to the Astronomical Almanac. University Science Books. p. 384. 
74. ^ Scott S. Sheppard. "The Jupiter Satellite Page". Carnegie Institution for Science, Department of Terrestrial Magnetism. http://www.dtm.ciw.edu/users/sheppard/satellites. Retrieved 2008-04-02. 
75. ^ Dan Bruton. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics & Astronomy (Stephen F. Austin State University). http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html. Retrieved 2009-01-20.