Solar System

For other uses, see Solar System (disambiguation).

Solar System
The Sun, planets, moons and dwarf planets[a]
(true color, size to scale, distances not to scale)
Age4.568 billion years[b]
Location
Nearest star
Population
StarsSun
Planets
Known dwarf planets
Known natural satellites758[D 3]
Known minor planets1,368,528[D 4]
Known comets4,591[D 4]
Planetary system
Star spectral typeG2V
Frost line~5 AU[5]
Semi-major axis of outermost planet30.07 AU[D 5] (Neptune)
Kuiper cliff50–70 AU[3][4]
Heliopausedetected at 120 AU[6]
Hill sphere1.1 pc (230,000 AU)[7] – 0.865 pc (178,419 AU)[8]
Orbit about Galactic Center
Invariable-to-galactic plane inclination~60°, to the ecliptic[c]
Distance to
Galactic Center
24,000–28,000 ly
[9]
Orbital speed
720,000 km/h (450,000 mi/h)[10]
Orbital period~230 million years[10]

The Solar System[d] is the gravitationally bound system of the Sun and the objects that orbit it.[11] It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Astronomers classify it as a G-type main-sequence star.

The largest objects that orbit the Sun are the eight planets. In order from the Sun, they are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn.

There is a strong consensus among astronomers[e] that the Solar System has at least nine dwarf planets: Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna. There are a vast number of small Solar System bodies, such as asteroids, comets, centaurs, meteoroids, and interplanetary dust clouds. Some of these bodies are in the asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit).[f] Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons'.

The Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere. Around 75–90 astronomical units from the Sun,[g] the solar wind is halted, resulting in the heliopause. This is the boundary of the Solar System to interstellar space. The outermost region of the Solar System is the theorized Oort cloud, the source for long-period comets, extending to a radius of 2,000–200,000 AU. The closest star to the Solar System, Proxima Centauri, is 4.25 light-years (269,000 AU) away. Both stars belong to the Milky Way galaxy.


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  1. ^ "Our Local Galactic Neighborhood". interstellar.jpl.nasa.gov. Interstellar Probe Project. NASA. 2000. Archived from the original on 21 November 2013. Retrieved 8 August 2012.
  2. ^ Hurt, R. (8 November 2017). "The Milky Way Galaxy". science.nasa.gov. Retrieved 19 April 2024.
  3. ^ Chiang, E. I.; Jordan, A. B.; Millis, R. L.; et al. (2003). "Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances". The Astronomical Journal. 126 (1): 430–443. arXiv:astro-ph/0301458. Bibcode:2003AJ....126..430C. doi:10.1086/375207. S2CID 54079935.
  4. ^ de la Fuente Marcos, C.; de la Fuente Marcos, R. (January 2024). "Past the outer rim, into the unknown: structures beyond the Kuiper Cliff". Monthly Notices of the Royal Astronomical Society Letters. 527 (1) (published 20 September 2023): L110–L114. arXiv:2309.03885. Bibcode:2024MNRAS.527L.110D. doi:10.1093/mnrasl/slad132. Archived from the original on 28 October 2023. Retrieved 28 September 2023.
  5. ^ Mumma, M. J.; Disanti, M. A.; Dello Russo, N.; et al. (2003). "Remote infrared observations of parent volatiles in comets: A window on the early solar system". Advances in Space Research. 31 (12): 2563–2575. Bibcode:2003AdSpR..31.2563M. CiteSeerX 10.1.1.575.5091. doi:10.1016/S0273-1177(03)00578-7.
  6. ^ Greicius, Tony (5 May 2015). "NASA Spacecraft Embarks on Historic Journey Into Interstellar Space". nasa.gov. Archived from the original on 11 June 2020. Retrieved 19 April 2024.
  7. ^ Chebotarev, G. A. (1 January 1963). "Gravitational Spheres of the Major Planets, Moon and Sun". Astronomicheskii Zhurnal. 40: 812. Bibcode:1964SvA.....7..618C. ISSN 0004-6299. Archived from the original on 7 May 2024. Retrieved 6 May 2024.
  8. ^ Souami, D; Cresson, J; Biernacki, C; Pierret, F (21 August 2020). "On the local and global properties of gravitational spheres of influence". Monthly Notices of the Royal Astronomical Society. 496 (4): 4287–4297. arXiv:2005.13059. doi:10.1093/mnras/staa1520.
  9. ^ Francis, Charles; Anderson, Erik (June 2014). "Two estimates of the distance to the Galactic Centre". Monthly Notices of the Royal Astronomical Society. 441 (2): 1105–1114. arXiv:1309.2629. Bibcode:2014MNRAS.441.1105F. doi:10.1093/mnras/stu631. S2CID 119235554.
  10. ^ a b "Sun: Facts". science.nasa.gov. Archived from the original on 19 April 2024. Retrieved 19 April 2024.
  11. ^ "IAU Office of Astronomy for Education". astro4edu.org. IAU Office of Astronomy for Education. Archived from the original on 11 December 2023. Retrieved 11 December 2023.
  12. ^ Standish, E. M. (April 2005). "The Astronomical Unit now". Proceedings of the International Astronomical Union. 2004 (IAUC196): 163–179. Bibcode:2005tvnv.conf..163S. doi:10.1017/S1743921305001365. S2CID 55944238.


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