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Solar System

Planets and dwarf planets of the Solar System. Compared with each other, the sizes are correct, but the distances are not

The Solar System is a group of space objects that are held together by gravity, with the Sun in the center. The Sun is a huge ball of hot glowing gas that gives off light and heat. Everything else in the Solar System moves around the Sun. The Solar System formed about 4.6 billion years ago when a giant cloud of gas and dust collapsed and started to spin. Most of the material went into forming the Sun, and the rest became planets and other objects. There are eight main planets, including Earth, and many moons that orbit them. There are also dwarf planets like Pluto, as well as asteroids, comets, meteoroids, and tiny particles called interplanetary dust. Our Solar System is part of a galaxy called the Milky Way. It lies in a part of the galaxy called the Orion Arm, about 27,000 light-years from the center of the Milky Way.[1][2][3][4]

There are eight planets in our Solar System. Starting from the closest to the Sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Scientists often group them into two main types. Terrestrial planets (Mercury, Venus, Earth, and Mars) are small and made mostly of rock and metal.[5] Giant planets include gas giants (Jupiter and Saturn), made mostly of hydrogen and helium,[6] and ice giants (Uranus and Neptune), which have more icy materials like water, methane, and ammonia.[7][8] Each planet moves around the Sun in an oval-shaped path called an ellipse.[9][10] These paths are all mostly in the same flat area of space, called the ecliptic plane.[11] Many planets have moons, which are natural objects that orbit them.[12] Some planets, like Saturn and Jupiter, also have rings made of ice and dust particles that circle around them.[13]

Far beyond the planet Neptune is a region called the Kuiper Belt. This area is filled with icy objects, including small worlds called dwarf planets, like Pluto, Haumea, and Makemake. These objects are made mostly of rock and ice and orbit the Sun just like the planets, but they are much smaller.[14] Even farther out is a zone called the scattered disk, and beyond that is a mysterious, faraway area called the Oort Cloud. Scientists think the Oort Cloud is a huge, invisible shell of icy objects surrounding the Solar System. It may be where long-period comets come from, those that take hundreds or thousands of years to travel around the Sun. These distant regions are at the edge of the Sun’s power.[15] The Sun’s gravity and solar wind stretch out to form a giant bubble called the heliosphere. This marks the boundary of the Sun’s influence, even farther than where the planets orbit.[16]

The Solar System has more than just planets and moons. It also has thousands of space rocks called asteroids.[17] Most of these are found in a big area between the planets Mars and Jupiter. This area is called the asteroid belt.[18] Some asteroids, called Trojan asteroids, share their paths around the Sun with planets.[19] There are also comets. Comets are made mostly of ice and dust. They move in long, stretched-out paths around the Sun. When a comet gets close to the Sun, the heat makes it grow a glowing tail that points away from the Sun.[20] Smaller pieces of rock and metal, called meteoroids, also float around in space. If one of these enters Earth’s atmosphere, it burns up and creates a bright streak in the sky. That’s what we call a meteor or a shooting star. If part of it survives the trip and lands on the ground, it is called a meteorite.[21]

The Sun is by far the biggest and most powerful object in the Solar System. It makes up more than 99.8% of all the mass, which means almost all the weight in the Solar System comes from the Sun. The Sun is a type of star that produces energy in its center through a process called nuclear fusion. This means it turns a gas called hydrogen into another gas called helium. When it does this, it releases a huge amount of energy. This energy spreads out in all directions as light, heat, and other types of radiation.[22] The Sun also sends out a flow of tiny, charged particles called the solar wind. This wind can hit the magnetic fields and atmospheres of planets like Earth. When this happens, it can cause things like the auroras, the colorful lights in the sky near the North and South Poles. The solar wind also affects space weather, which can sometimes interfere with satellites and power systems on Earth.[23]

Scientists believe the Solar System formed from a big spinning cloud of gas and dust. This idea is called the nebular hypothesis. Over time, the cloud began to collapse and spin faster, forming a flat disk. Most of the material gathered in the center to form the Sun, while the rest started forming planets. Closer to the Sun, it was very hot, so only rocky materials could stick together. That’s why the inner planets like Mercury, Venus, Earth, and Mars are made of rock. Farther out, it was much colder, so gases and ices could join together to form the giant planets like Jupiter and Saturn. Over billions of years, the planets moved around, crashed into other objects, and were affected by gravity. These changes helped shape the Solar System into the way we see it today.[24][25]

People have been studying the Solar System for thousands of years. Ancient civilizations watched the sky and noticed how the planets and stars moved. They used this knowledge to make calendars and guide their lives.[26] A big change came in the 1500s, when a man named Nicolaus Copernicus said that the Sun, not the Earth, was at the center of the Solar System. This idea is called the heliocentric model, and it replaced the older belief that everything moved around the Earth. It was a major turning point in how people understood space.[27][28] Later, in the 1600s, Isaac Newton came up with the laws of motion and gravity. These laws helped explain how the planets move and why they stay in orbit around the Sun.[29] In more recent times, the 1900s and 2000s, we have sent robotic spacecraft to explore the Solar System. Missions like Voyager, Cassini, Juno, and the Mars rovers have taught us a lot about the planets, moons, and even the chance of finding life somewhere else in space.[30][31][32][33]

  1. ↑ Hansen, C.J.; Kawaler, S.A.; Trimble, V. (2004). Stellar interiors: physical principles, structure, and evolution (2nd ed.). Springer. pp. 19–20. ISBN 978-0-387-20089-7.
  2. ↑ Connelly, James N.; et al. (2012). "The absolute chronology and thermal processing of solids in the Solar protoplanetary disk". Science. 338 (6107): 651–655. Bibcode:2012Sci...338..651C. doi:10.1126/science.1226919. ISSN 0036-8075. PMID 23118187. S2CID 21965292.
  3. ↑ "The Solar System: our celestial neighbourhood". Australian Environmental Education. Retrieved 2025-07-03.
  4. ↑ Gillessen, S.; Plewa, P. M.; Eisenhauer, F.; Sari, R.; Waisberg, I.; Habibi, M.; Pfuhl, O.; George, E.; Dexter, J.; Fellenberg, S. von; Ott, T. (2017-03-01). "An Update on Monitoring Stellar Orbits in the Galactic Center". The Astrophysical Journal. 837 (1): 30. doi:10.3847/1538-4357/aa5c41. ISSN 0004-637X.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  5. ↑ "Terrestrial - NASA Science". 2020-10-22. Retrieved 2025-07-03.
  6. ↑ "Gas Giant - NASA Science". 2020-10-22. Retrieved 2025-07-03.
  7. ↑ "The Realm of the Ice Giants". The Planetary Society. Retrieved 2025-07-03.
  8. ↑ "Ice Giant Resources - NASA Science". 2024-07-21. Retrieved 2025-07-03.
  9. ↑ "Ellipses and Elliptic Orbits". hyperphysics.phy-astr.gsu.edu. Retrieved 2025-07-03.
  10. ↑ "1.4: Elliptic Orbits - Paths to the Planets". Physics LibreTexts. 2015-11-07. Retrieved 2025-07-03.
  11. ↑ "What Is the Plane of the Ecliptic? - NASA". Retrieved 2025-07-03.
  12. ↑ "Moons". 2023-05-31. Retrieved 2025-07-03.
  13. ↑ "12.5: Planetary Rings". Physics LibreTexts. 2016-10-07. Retrieved 2025-07-03.
  14. ↑ "Kuiper Belt: Facts - NASA Science". 2017-11-14. Retrieved 2025-07-03.
  15. ↑ "Oort Cloud: Facts - NASA Science". 2017-11-14. Retrieved 2025-07-03.
  16. ↑ "Components of the Heliosphere - NASA". Retrieved 2025-07-03.
  17. ↑ "Asteroids". 2017-10-26. Retrieved 2025-07-03.
  18. ↑ "Asteroid Facts". 2017-11-14. Retrieved 2025-07-03.
  19. ↑ "What are the Trojan Asteroids? We Asked a NASA Scientist: Episode 8 - NASA". Retrieved 2025-07-03.
  20. ↑ "Comet Facts". 2017-11-14. Retrieved 2025-07-03.
  21. ↑ "Meteors and Meteorites: Facts - NASA Science". 2017-11-30. Retrieved 2025-07-03.
  22. ↑ "Sun: Facts - NASA Science". 2017-11-14. Retrieved 2025-07-03.
  23. ↑ "What Is the Solar Wind? - NASA Science". 2024-11-19. Retrieved 2025-07-03.
  24. ↑ "8.2: Origin of the Solar System—The Nebular Hypothesis". Geosciences LibreTexts. 2019-11-04. Retrieved 2025-07-03.
  25. ↑ "How Our Solar System Formed". www.khanacademy.org. Retrieved 2025-07-03.
  26. ↑ wpadmin (2018-11-26). "7 Ancient Cultures and How They Shaped Astronomy". IAU Office of Astronomy for Development. Retrieved 2025-07-03.
  27. ↑ Draper J.W. 1874. History of the conflict between religion and science. New York: D. Appleton 1874, p172–173. ISBN 978-1-59102-533-7
  28. ↑ "Heliocentrism | Definition, History, & Facts | Britannica". www.britannica.com. Retrieved 2025-07-03.
  29. ↑ "Newton's law of gravitation | Definition, Formula, & Facts | Britannica". www.britannica.com. 2025-06-20. Retrieved 2025-07-03.
  30. ↑ "Mission Overview - NASA Science". 2024-04-09. Retrieved 2025-07-03.
  31. ↑ "Cassini: About the Mission - NASA Science". 2018-08-21. Retrieved 2025-07-03.
  32. ↑ "Juno - NASA Science". 2023-06-15. Retrieved 2025-07-03.
  33. ↑ "Mars Exploration Rovers: Spirit and Opportunity - NASA Science". 2024-03-22. Retrieved 2025-07-03.
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