Section: 14 | Properties of the Solar System |

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PROPERTIES OF THE SOLAR SYSTEM

Our solar system consists of eight major planets and numerous other objects (Ref. 1) that have been observed orbiting the Sun. These include the following.

Dwarf planets: five (Ref. 2)
Minor planets: 1 026 572 through December 14, 2020 (Ref. 1)
Asteroids: more than 1 047 527 through December 14, 2020 (Ref. 3)
Asteroid belts: between Mars and Jupiter
Satellites (moons): associated with specific planets; see “Satellites of the Planets” in this section
Comets: 4535 through December 14, 2020 (Ref. 1)

Improved optical and non-optical telescopes (Ref. 4) constantly add new objects to the list.

Dwarf planets are defined by the International Astronomical Union (Ref. 2) as bodies in orbit around the Sun massive enough to adopt a near-spherical shape because of their self-gravity, but are appreciably smaller than the eight major planets. Plutoids form a subset of the dwarf planets, with orbits larger than that of Neptune (Ref. 5). As of 2020, the IAU has recognized the names of four plutoids: Pluto, Eris, Haumea, and Makemake. Because Ceres has an orbit much smaller than Neptune, it is classified as a dwarf planet but not as a plutoid. Data in these tables are drawn from many references as indicated. See Refs. 17-19 for additional information.

The following tables contain various properties about our solar system.

Table No.	Contents
1	Properties of the Planetary System
2	Properties of the Sun
3	Orbital Properties of the Major and Important Dwarf Planets
4	Physical Properties of the Major and Important Dwarf Planets and the Moon
5	Mean Surface Temperature and Pressure and Atmospheric Composition of the Major Planets and Pluto

References

IAU Minor Planet Center, retrieved 31 January 2021. <www.minorplanetcenter.net>
Dwarf Planets, IAU Minor Planet Center, retrieved January 3, 2021. <www.minorplanetcenter.net/dwarf_planets>
Asteroids, NASA Science Solar System Exploration, retrieved January31, 2021. <solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/overview/?page=0&per_page=40&order=name+asc&search=&condition_1=101%3Aparent_id&condition_2=asteroid%3Abody_type%3Ailike>
The Multiwavelength Milky Way: Telescopes, NASA, Goddard Space Flight Center, retrieved January 31, 2021. <asd.gsfc.nasa.gov/archive/mvmw/mmw_telescope.html>
IAU Press Release, <www.iau.org/public_press/news/release/iau0804>, June 2008.
Lang, K. R., Astrophysical Data: Planets and Stars, Springer-Verlag, New York, 1992. [https://doi.org/10.1007/978-1-4684-0640-5_3]
Cox, A. N., Allen’s Astrophysical Quantities, Fourth Edition, Springer-Verlag, New York, 2000; this is a revision of Allen, C. W., Astrophysical Quantities, Third Edition, 1983.
Planetary Fact Sheet - Metric, NASA Goddard Space Flight Center, retrieved January 31, 2021. <nssdc.gsfc.nasa.gov/planetary/factsheet>
Sun Fact Sheet, NASA Goddard Space Flight Center, retrieved January 31, 2021. <nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html>
See individual fact sheets for each planet at Planetary Facts Sheets, National Space Science Data Center, NASA Goddard Space Flight Center, retrieved January 31, 2021. <nssdc.gsfc.nasa.gov/planetary/planetfact.html>
Data available at JPL Small-Body Database Browser search engine using name of dwarf planet, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, retreived January 31, 2021. <ssd.jpl.nasa.gov/sbdb.cgi>
The Planetary Society, <www.planetary.org/explore/topics/groups/our_solar_system/>.
The Astronomical Almanac for the Year 2019, U.S. Government Printing Office, Washington, DC, 2005; available online at <asa.usno.navy.mil/>.
Arnet, B., The Nine Planets, <www.nineplanets.org>.
Onasch, B., Our Solar System, <www.onasch.de/astro/>.
Killen, R., Cremonese, G., Lammer, H. et al, Space Science Reviews 132, 433-509, 2007. <doi: 10.1007/s11214-007-9232-0> [https://doi.org/10.1007/s11214-007-9232-0]
K. A. Olive et al. (Particle Data Group), Chin. Phys. C 38(9), 090001, 2014.; section on astrophysical constants available at <pdg.lbl.gov/2014/reviews/astrorpp.pdf>, [https://doi.org/10.1088/1674-1137/38/9/090001]
Seidelmann, P. K., Editor, Explanatory Supplement to the Astronomical Almanac, University Science Books, Mill Valley, CA, 1992.
Kopp, G., and Lean, J. L., Geophys. Res. Lett. 38 (1), 2011. [https://doi.org/10.1029/2010GL045777]

Properties of the Planetary System

Our planetary system, which includes all major and dwarf planets as well as other objects that orbit the Sun, has been the object of research and wonder since ancient times. Ancient observers clearly recognized that several objects in the night sky had different motion from more fixed objects (i.e., stars) and over the centuries, considerable effort was expended to explain this motion. Nicolas Copernicus’ work first published in 1542 provided the foundation for our present-day helio-centric view of the solar system. Many refinements to the theory have been made since Copernicus’ first publication.

Table 1 presents data for several properties of the planetary system as a whole (Refs. 6-8). The mass of the Earth is included as it is often used as a reference point for masses of objects in the solar system.

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TABLE 1. Properties of the Planetary System

Property	Value
Mass of the Earth (M_e)	5.9723 × 10²⁴ kg
Total mass of planetary system	2.669 × 10²⁷ kg
	447 M_e
Total angular momentum of planetary system	3.148 × 10⁴⁸ kg m² s^-1
Total kinetic energy of planets	1.99 × 10³⁵ J
Total rotational energy of planets	0.7 × 10³⁵ J

Properties of the Sun

The Sun is a star categorized as a G-type, yellow-dwarf, main sequence star. Table 2 contains important properties of the Sun (Ref. 9) except as noted.

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TABLE 2. Properties of the Sun

Property	Value
Mass	1.9885 × 10³⁰ kg
	3329483 M_e
Radius	6.95700 × 10⁵ km
Surface area	6.079 × 10¹² km²
Volume	1.412 × 10¹⁸ km³
Mean density	1.408 g cm^-3
Surface gravity	274.0 m s^-2
Surface escape velocity	617.6 × 10⁵ km s^-1
Effective temperature	5772 K
Luminosity (Total radiant power emitted)	3.828 × 10²⁶ W
Flux of radiant energy at the Earth (Solar constant) (Ref. 11)	1360.8 W m^-2
Surface flux of radiant energy*	6.293 × 10⁷ W m^-2
Mass conversion rate	4260 × 10⁶ kg s^-1
Mean energy production	0.195 × 10^-3 J kg^-1 s^-1
Sidereal rotation period (at 16 deg. latitude)	609.12 h

^*Calculated with Stefan-Boltzmann law with T = 5772 K.

Orbital Properties of the Major and Important Dwarf Planets

Table 3 has orbital and related properties for the major (Ref. 10) and dwarf planets (Ref. 11). Additional property information is available in Refs. 12-15. These properties for the major planets are well established, though given that the planets are dynamic, i.e., bodies that evolve over time with consequent small changes in orbits and rotation. Column definitions for Table 3 are as follows. Note: 1 astronomical unit (au) = 149 597 870.700 km.

Column heading	Definition
Planet	Name of planet; the IAU number for plutoids is given in parentheses; Ceres is designated as minor planet 1
Year of discovery	Year of first observation; note Galileo made the first telescopic observations of Venus, Jupiter, and Saturn in 1609-1610
Dist. to Sun	Distance to the Sun, in au
Sidereal orbit period	Time, in years, it takes the planet to make revolution around the Sun relative to the fixed stars; for Pluto, it is the time from the last zero longitude crossing to the next (July 24, 1820 to July 2, 2068); all planet orbits are prograde, that is, in the direction of the Sun’s rotation
Sidereal rotational period (days)	Time, in days, for one rotation of the planet on its axis relative to the fixed stars; a minus sign indicates retrograde rotation, that is, the rotation is opposite to the orbital motion
Sidereal rotational period (hours)	Sidereal rotational period, in hours
Perihelion	Point in the planet’s orbit closest to the Sun, in au
Aphelion	Point in the planet’s orbit farthest from the Sun, in au
Semimajor axis	Mean distance from the Sun, in au, from center to center
Orbit eccentricity	Measure of the circularity of the orbit, equal to the difference between the aphelion and perihelion distance divided by twice the semimajor axis; also expresses the shape of the ellipse
Orbit inclination	Inclination, in degrees, of the orbit to the ecliptic; for planets, the ecliptic is the Earth’s orbit; sometimes the orbit inclination is simply called the ecliptic
Inclination of equator	Angle, in degrees, between the equator and orbital plane with north defined as the pole axis above (north by the right-hand rule) the plane of the solar system; also known as the axial tilt

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TABLE 3. Orbital Properties of the Major and Important Dwarf Planets

Planet	Year of discovery	Dist. to Sun/ au	Sidereal orbit period/ y	Sidereal rotational period (days)/ d	Sidereal rotational period (hours)/ hr	Perihelion/ au	Aphelion/ au	Semimajor axis/ au	Orbit eccentricity(ε)	Orbit inclination/ deg.	Inclination of equator/ deg.
Major Planets
Mercury	Ancient	0.3871	0.2408467	58.6462	1407.51	0.307720094	0.467025212	0.387369308	0.20563	7.0049°	0.01°
Venus	Ancient	0.723332	0.61519726	-243.018	-5832.6	0.718936673	0.728723084	0.723839912	0.006773	3.3947°	177.36°
Earth		1	1.0000174	0.99726968	23.9345	0.983992562	1.017438944	1.000715753	0.01671	0°	23.45°
Mars	Ancient	1.52366	1.8808476	1.02595676	24.6229	1.382118226	1.667161673	1.52463995	0.09341	1.8506°	25.19°
Jupiter	700-800 BCE	5.20336	11.862615	0.41354	9.925	4.953556354	5.462583532	5.208069943	0.048392	1.3053°	3.12°
Saturn	700 BCE	9.53707	29.447498	0.44401	10.656	9.04761427	10.1309359	9.589271738	0.05415	2.484°	26.73°
Uranus	1781	19.19126	84.016846	-0.71833	-17.24	18.33732683	20.09207789	19.21469902	0.04717	0.7699°	97.86°
Neptune	1846	30.06896	164.79132	0.67125	16.11	29.7301479	30.40724984	30.06869887	0.008586	1.769°	28.32°
Dwarf Planets
Pluto (134340)	1930	39.48168	247.74	-6.3872	-153.2928	29.666	48.860	39.263	0.2444	17.14°	57.47°
Eris (136199)	2005	67.7	559.07	1.0792		38.272	97.456	67.864	0.4360	44.0°
Haumea (136108)	2004	43.13	283.77	0.163139	3.8	34.767	51.598	43.182	0.1949	28.2°
Makemake (136472)	2005	45.79	306.21	0.951108		38.105	52.756	45.431	0.1613	29.0°
Ceres (1)	1801	2.77	4.61	0.3780904	9.074	2.5587	2.9796	2.7692	0.0760	10.587°	3°

Physical Properties of the Major and Important Dwarf Planets and the Moon

Table 4 has physical and related properties for the major and important dwarf planets. The Moon is included for ease of comparison. These properties, for the most part, are well established for the major planets. For the dwarf planets, the properties are not well established or not measured at the present time. Refs. 10-11 contain further information.

Column definitions for Table 4 are as follows.

Column heading	Definition
Planet	Name of planet; the IAU number for plutoids is given in parentheses; Ceres is designated minor planet 1
Mass	Mass of the planet, in units 10²⁴ kg
Equit. radius	Radius of the planet at the equator, in km; * indicates mean radius
Polar radius	Radius of the planet at the poles, in km
Volume	Volume of planet, in units 10¹⁰ km³
Density	Mean density of the planet (mass/volume), in g cm^-3
Flattening	Ratio of (equatorial radius – polar radius)/(equatorial radius)
Surface gravity	Equatorial gravitational acceleration at the surface of the planet or the 1 bar level, not including the effect of rotation, in units m s^-2
Escape velocity	Initial velocity required to escape the planet’s gravitational pull, in km s^-1
Geometric albedo	Ratio of the planet’s brightness at a phase angle of zero to the brightness of a perfectly diffusing disk with the same position and apparent size; its value for the Earth is highly variable
No. of satellites	Number of detected satellites orbiting the planet

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TABLE 4. Physical Properties of the Major and Important Dwarf Planets and the Moon

Planet	Mass/ 10²⁴ kg	Equit. radius/ km	Polar radius/ km	Volume/ 10¹⁰ km³	Density/ g cm^-3	Flattening	Surface gravity/ m s^-2	Escape velocity/ km s^-1	Geometric albedo	No. of satellites
Mercury	0.33011	2440.53	2439.7	6.083	5.427	0	3.70	4.25	0.142	0
Venus	4.8675	6051.8	6051.8	92.843	5.243	0	8.87	10.36	0.689	0
Earth	5.9724	6378.1366	6356.8	108.321	5.514	0.003353	9.80	11.186	0.434	1
(Moon)	0.073483	1738.1	1736.0	2.1968	3.344	0.0012	1.62	2.38	0.12
Mars	0.64171	3396.2	3376.2	16.318	3.934	0.00589	3.71	5.03	0.170	2
Jupiter	1898.19	71492	66854	143128	1.326	0.06487	24.79	60.20	0.538	79
Saturn	568.34	60268	54364	82713	0.687	0.09796	10.44	36.09	0.499	82
Uranus	86.813	25559	24973	6833	1.270	0.02293	8.87	21.38	0.51	27
Neptune	102.413	24764	24341	6254	1.638	0.01708	11.15	23.56	0.442	14
Pluto (134340)	0.01303	1188	1188	0.702	1.89	0	0.62	1.21	0.52	5
Eris (136199)	0.01466	1163*		0.659	2.43		0.82	1.38	0.96	1
Haumea (136108)	0.004006	780-798*		0.198	1.75-2.02		0.401	0.809	<0.51
Makemake (136472)	0.0031	715-739*		0.153	1.7-2.1		<0.57	<0.91	0.81
Ceres (1)	0.000943	469*		0.434	2.162		27	0.51	0.09

Other Characteristics of the Major Planets and Pluto

Table 5 contains data on the mean surface temperature and pressure as well as the atmospheric composition for the major planets and Pluto (Ref. 10). Data for Mercury are from Ref. 16. Column definitions for Table 5 are as follows.

Column heading	Definition
Planet	Name of planet
T_sur	Mean surface temperature, in K
P_sur	Mean surface pressure, in bar
CO₂, N₂, O₂, etc.	Concentration of gases as indicated by molecular formula in planetary atmosphere; in units as specified

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TABLE 5. Mean Surface Temperature and Pressure and Atmospheric Composition of the Major Planets and Pluto

Planet	T_sur/K	P_sur/bar	CO₂	N₂	O₂	H₂O	H₂	He	Ar	Ne	CO	CH₄
Mercury	440	< ~5 ×10^-15	Trace	Trace	<9 × 10¹⁴ cm^-2*	< 1 × 10¹² cm^-2*	Trace	< 3 × 10¹¹ cm^-2*	~ 1.3 × 10⁹ cm^-2*	Trace
Venus	737	92	96.5%	3.5%	69 ppm	20 ppm		12 ppm	70 ppm	7 ppm	17 ppm
Earth	288	1.014	410 ppm	78.084%	20.946%	0 to 3%	0.55 ppm	5.24 ppm	9340 ppm	18.18 ppm	1 ppm	1.7 ppm
Mars	210	0.004 to 0.0087^a	95.17%	2.59%	0.16%	210 ppm			1.94%	2.5 ppm	0.06%
Jupiter	165	>>1000				4 ppm	89.8%	10.2%				3000 ppm
Saturn	134	>>1000					96.3%	3.25%				4500 ppm
Uranus	76	>>1000					82.5%	15.2%				2.3%
Neptune	72						80.0%	19.0%				1.5%
Pluto	31^b	~0.000013		99.0%							0.05%	0.5%

^*These values are for column density, that is, the number of atoms or molecules in a vertical column of 1 cm².
^aThe surface temperature on Mars varies with its seasons.
^bSurface temperature values for Pluto range from 24 to 38 K.

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PROPERTIES OF THE SOLAR SYSTEM

References

Properties of the Planetary System

TABLE 1. Properties of the Planetary System

Properties of the Sun

TABLE 2. Properties of the Sun

Orbital Properties of the Major and Important Dwarf Planets

TABLE 3. Orbital Properties of the Major and Important Dwarf Planets

Physical Properties of the Major and Important Dwarf Planets and the Moon

TABLE 4. Physical Properties of the Major and Important Dwarf Planets and the Moon

Other Characteristics of the Major Planets and Pluto

TABLE 5. Mean Surface Temperature and Pressure and Atmospheric Composition of the Major Planets and Pluto

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