List of gravitationally rounded objects of the Solar System

Objects in the
Solar System
Categories

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.

Contents

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

Book: Solar System
Wikipedia books are collections of articles that can be downloaded or ordered in print.


Notes

Unless otherwise cited:[ac]

  1. ^ 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]
  2. ^ Saturn satellite info taken from NASA Saturnian Satellite Fact Sheet.[69]
  3. ^ 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.
  4. ^ Uranus satellite info taken from NASA Uranian Satellite Fact Sheet.[72]
  5. ^ Radii for plutoid candidates taken from material published by John Stansberry et al.[20]
  6. ^ 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]
  7. ^ 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).
  6. ^ Orbital speed is calculated using the mean orbital radius and the orbital period, assuming a circular orbit.
  7. ^ Assuming Pluto's density of 2.0
  8. ^ Calculated using the formula \begin{smallmatrix}T\ =\ \frac{T_{\textrm{eff}}(1-qp_{\nu})^{1/4}}{\sqrt{2}}\sqrt{52/r},\end{smallmatrix} where Teff =54.8 K at 52 AU, p_{\nu} 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 \pi was replaced with 4 accounting for the difference between circle and sphere. All parameters mentioned above were taken from the same paper.
  9. ^ 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

  1. ^ Derived from density
  2. ^ Surface area was calculated using the formula for a scalene ellipsoid:
    \begin{smallmatrix}2\pi\left(c^2%2Bb\sqrt{a^2-c^2}E(\alpha,m)%2B\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

  1. ^ Relative to Earth
  2. ^ sidereal
  3. ^ retrograde
  4. ^ The inclination of the body's equator from its orbit.
  5. ^ At pressure of 1 bar
  6. ^ At sea level
  7. ^ The ratio between the mass of the object and those in its immediate neighborhood. Used to distinguish between a planet and a dwarf planet.
  8. ^ This object's rotation is synchronous with its orbital period, meaning that it only ever shows one face to its primary.
  9. ^ 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.
  10. ^ Proteus average diameter: 210 km;[44] Mimas average diameter: 199 km[69]
  11. ^ "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. 
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