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Solar System

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TheSolar Systemis theSunand all the objects that travel around it. The Sun isorbitedbyplanets,asteroids,cometsand other things.

Planetsanddwarf planetsof the Solar System. Compared with each other, the sizes are correct, but the distances are not

The Solar System is about 4.568billionyears old.[1]The Sun formed bygravityin a largemolecular cloud.It is mainlyhydrogen,which it converts intoheliumthroughnuclear fusion.The planets are in a flattened orbiting disk. This disk was partly left over from the cloud that formed the Sun, plus other material as the Sun moved through space. Eventually, the gas and dust of the diskcame together into planets.It is thought that almost all stars and their planetsform this way.

The Sun is astar.It makes up 99.9% of the Solar System'smass.[2]This means that it has stronggravity.The other objects are pulled into orbit around the Sun. The Sun is mostly made out ofhydrogen,and someheliumand higher elements. All heavier elements, calledmetalsin astronomy, account for less than 2% of the Sun's mass. Oxygen is about 1% of the Sun's mass. Iron (0.2%) is the most plentiful of the other elements.[3]

There are eightplanetsin the Solar System. From closest to farthest from the Sun, they are:Mercury,Venus,Earth,Mars,Jupiter,Saturn,UranusandNeptune.The first four planets are calledterrestrial planets.They are mostly made ofrockandmetal,and they are mostlysolid.The last four planets are calledgas giants.This is because they are much larger than other planets and are mostly made ofgas.

Six of the planets, and the six largest dwarf planets, are orbited bymoons.There are more than 200 moons in the Solar System. Mercury and Venus have no moons, and Jupiter and Saturn have the largest number of moons. The largest moon isGanymedewhich is a moon of Jupiter.Titanis one of Saturn’s moons. It is the only moon in the Solar System to have anatmosphere,which is mainly composed ofnitrogen.

The Solar System also contains other things. There areasteroid belts,mostly between Mars and Jupiter. Further out than Neptune, there is theKuiper beltand thescattered disc.These areas havedwarf planets,includingPluto,Makemake,Haumea,CeresandEris.There are thousands of very small objects in these areas. There are also comets,centaurs,andinterplanetary dust.

InAncient Greece,Aristarchus of Samosproposed the heliocentric model of the Solar System, where the Sun, is at the center of the known universe. He is sometimes known as the "Greek Copernicus".[4]

Evolution of the Solar System[change|change source]

See the main article:Formation and evolution of the Solar System

The formation andevolutionof the Solar System began 4.6billionyears ago with thegravitationalcollapse of a small part of a giantmolecular cloud.[5]

Most of the collapsing mass collected in the centre, forming theSun,while the rest flattened into a protoplanetarydiskof loose dust, out of which theplanets,moons,asteroids,and other Solar System bodies formed.

This model, known as thenebularhypothesis,was developed in the 18th (1700s) century byEmanuel Swedenborg,Immanuel Kant,andPierre-Simon Laplace.It has been adjusted by scientific disciplines such asastronomy,physics,geology,andplanetary science.As our knowledge of space has grown, the models have been changed to account for the new observations.

The Solar System has evolved considerably since its initial formation. Some moons have formed from circling discs of gas and dust around their parent planets, while other moons are believed to have formed and were later captured by their planets. Others, such as theEarth'sMoon,may be the result ofgiant collisions.

Many collisions between bodies have occurred, and have been important to the evolution of the Solar System. In the early stages, the positions of the planets sometimes shifted, and planets have switched places.[6][7]This planetary migration is thought to have been responsible for much of the Solar System's early evolution.

Grand tack hypothesis[change|change source]

Astronomers now think that the order of the planets was not always as it is today. Knowing what we know today, we can see the Solar System is strange. Most other planetary system we are able to study have their largest planet closer to their star. In the Solar System it is not. Also we have noticed other oddities in the Solar System. Mars is smaller than it ought to be, and the asteroid belt has been disturbed.

So, astronomers have put forward thegrand tack hypothesis.In itJupiterwas earlier closer to the Sun, and (for some unknown reason) moved out to its present position.

Orbits of the planets[change|change source]

TheEarth's orbitaround the Sun is nearly a perfect circle, but in a very slightly oval shaped orbit, anelliptical orbit.The otherplanetsin the Solar System also orbit the Sun in slightly elliptical orbits.Mercuryhas a more elliptical orbit than the others, and there is obviously some explanation for this. Some of the smaller objects orbit the Sun in veryeccentric orbits.The planets all orbit the Sun in the same direction.[8]: 4–5 

A full account of the planetary motion needs an account of then-body problem, which is not treated on this wiki. A page can be found on En wiki.

Discovery and exploration[change|change source]

See the main article:History of astronomy

For thousands of years, people had no need for a name for the "Solar System". They thought the Earth stayed still at the center of everything (geocentrism). The Greek philosopherAristarchus of Samossuggested that there was a special order in the sky.[9]Nicolaus Copernicuswas the first to develop amathematical systemthat described what we now call the "Solar System". This was called a "new system of the world". In the 17th century,Galileo Galilei,Johannes KeplerandIsaac Newtonbegan to understandphysicsmore clearly. People began to accept the idea that the Earth is a planet that moves around the Sun, and that the planets are worlds, and that all worlds are governed by the same samephysical laws.More recently, telescopes andspace probessometimes let us see details directly. All inner planets have surface features. The gas giants (as the name suggests) have surfaces whose make-up is gradually being discovered.

The eight planets[change|change source]

Planetary distances, not to scale

In their order from the Sun:

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune

The planets are the biggest objects that go around the Sun. It took people many years of usingtelescopesto find the objects that were farthest away.New planetsmight still be found, and more small objects are found every year. Most of the planets havemoonsthat orbit around them just as the planets orbit the Sun. There are at least 200 of these moons in the Solar System.

Dwarf planets[change|change source]

See the main article:Dwarf planet

Pluto was discovered by American astronomerClyde Tombaughand was declared the 9th planet of the Solar System in 1930.

This all changed on August 24, 2006, when the International Astronomical Union (IAU) decided on the correct definition for the word "planet" for the first time. By this definition, Pluto was not a planet anymore due to its irregular orbit and size. It became a "dwarf planet" along with Eris and many others.

Eris was 27% more massive than Pluto. After this, Pluto was put on the list of minor planets and was downgraded in 2006.[10]Instead they defined a new category ofdwarf planet,into which Pluto did fit, along with some others. These small planets are sometimes calledplutinos.

Structure[change|change source]

There are a few main parts of the Solar System. Here they are in order from the Sun, with the planets numbered, and thedwarf planetsmarked with the letters a to e.

Inner solar system[change|change source]

The inner planets. From left to right:Mercury,Venus,Earth,andMars

The first four planets closest to the Sun are called the inner planets. They are small and dense terrestrial planets, with solid surfaces. They are made up of mostly rock and metal with a distinct internal structure and a similar size. Three also have anatmosphere.The study of the four planets gives information aboutgeologyoutside the Earth.

Outer solar system[change|change source]

The outer planets: From left to right:Jupiter,Saturn,Uranus,andNeptune

Trans-Neptune region[change|change source]

Oort Cloud[change|change source]

TheOort cloudis separate from thetrans-Neptune region,and much farther out. It contains the long-periodcomets.

Ecliptic plane[change|change source]

Theplane of theeclipticis defined by the Earth's orbit around the Sun. All of the planets orbit the Sun roughly around this sameorbital plane.The farther away from this plane a planet orbits, the moreinclinedis its orbit to the ecliptic. If you could look at the Solar System "edge on" then all the planets would be orbiting more or less in the plane of the ecliptic.

References[change|change source]

  1. ↑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.PMID23118187.S2CID21965292.
  2. ↑More precisely, 99.86 of itsknownmass. The total mass of the bodies in theOort cloudis not known. Jupiter and Saturn account for 90% of the remaining 0.14%.
  3. ↑ Hansen, C.J.; Kawaler, S.A.; Trimble, V. (2004).Stellar interiors: physical principles, structure, and evolution(2nd ed.). Springer. pp. 19–20.ISBN978-0-387-20089-7.
  4. ↑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
  5. ↑Bouvier, Audrey; Wadhwa, Meenakshi (2010), "The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion.",Nature Geoscience,3(9): 637–641,Bibcode:2010NatGe...3..637B,doi:10.1038/ngeo941
    Date based on oldest inclusions found to date inmeteorites,thought to be among the first solid material to form in the collapsing solar nebula.
  6. ↑R. Gomes H.F.; et al. (2005)."Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets"(PDF).Nature.435(7041): 466–469.Bibcode:2005Natur.435..466G.doi:10.1038/nature03676.PMID15917802.S2CID4398337.
  7. ↑A. Morbidelli J.; et al. (2000)."Source regions and timescales for the delivery of water to the Earth".Meteoritics & Planetary Science.35(6): 1309–1320.Bibcode:2000M&PS...35.1309M.doi:10.1111/j.1945-5100.2000.tb01518.x.ISSN1086-9379.S2CID129817341.
  8. ↑Chambers, John; Mitton, Jacqueline (2014).From dust to life: the origin and evolution of our solar system.Princeton, New Jersey: Princeton University Press.ISBN978-0-691-14522-8.OCLC859181634.
  9. ↑WC Rufus (1923)."The astronomical system of Copernicus".Popular Astronomy.31:510.Bibcode:1923PA.....31..510R.Retrieved2009-05-09.
  10. ↑"IAU 2006 General Assembly: Result of the IAU Resolution votes".IAU.Retrieved2018-09-04.

More reading[change|change source]

  • Lang, Kenneth R. (2011).The Cambridge Guide to the Solar System(2nd ed.). Cambridge University Press.ISBN978-0521198578.
  • Iggulden, Hal; Iggulden, Conn (2007). "The Solar System (a quick reference guide)".The Dangerous Book for Boys.New York: HarperCollins. pp. 217–224.ISBN978-0061243585.
  • Thierry Montmerle; Jean-Charles Augereau; Marc Chaussidon 2006.Solar System formation and early evolution: the first 100 million years. Earth, Moon, and Planets.Springer.98(1–4): 39–95. Bibcode:2006EM&P...98...39M. doi:10.1007/s11038-006-9087-5. S2CID 120504344.

Other websites[change|change source]

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