Stars form from clouds of dust and gas that collapse under their own gravity. As the cloud collapses, a hot protostar forms at the center. Nearby clouds may break into blobs, explaining why most stars exist in pairs or groups. Planets form from disks of dust and gas that surround young stars. As the disk spins, dust clumps stick together, growing into planetesimals that eventually collide and merge into planets. Moons can form alongside planets from leftover material, be captured asteroids, or form from debris after a large impact. Eventually the sun will run out of hydrogen fuel and expand into a red giant, likely consuming the inner planets before collapsing into a white dwarf.

1. Formations of the Solar System

2. Formation of Stars Stars are born in clouds of dust. Turmoil deep in these clouds makes knots with sufficient mass that the gas and dust begin to collapse under their own gravitational pull. As the cloud collapses, the material in the middle begins to heat up. Known as a protostar, it is this hot core at the center of the collapsing cloud that will one day become a star.

3. Formation of Stars (continued) Three-dimensional computer models of star formation predict that the spinning clouds of collapsing gas and dust may break up into two or three blobs; this would explain why the majority the stars in the Milky Way are paired or in groups of multiple stars. As the cloud collapses, a dense, hot core forms and begins gathering dust and gas. Not all of this material ends up as part of a star — the remaining dust can become planets, asteroids, or comets or may remain as dust.

4. Formation of Planets Since we only see the end result of planet formation, not the process itself, we do not fully know how planets came to be. We only have theories. The most common is this: According to our current understanding, a star and its planets form out of a collapsing cloud of dust and gas within a larger cloud called a nebula. As gravity pulls material in the collapsing cloud closer together, the center of the cloud gets more and more compressed and, in turn, gets hotter. This dense, hot core is the beginning of a new star. Meanwhile, motions within the collapsing cloud cause it to churn. As the cloud compresses , it begins to rotate in the same direction. The rotating cloud eventually flattens into a disk that gets thinner as it spins. These "circumstellar" or "protoplanetary" disks are the birthplaces of planets .

5. Formation of Planets (continued) As a disk spins, the material within it travels around the star in the same direction. Eventually, the material in the disk will begin to stick together. As these small clumps orbit within the disk, they sweep up surrounding material, growing bigger and bigger. The gravity of the bigger chunks start to attract dust and other clumps. They pull all of this stuff in, getting bigger and bigger. The bigger a chunk is, the more stuff it attracts. Soon the “planetesimals” are taking shape.

6. Formation of Planets (continued version 2.0) Since hundreds of these planetesimals are forming at the same time, inevitably they meet up. If their paths cross at just the right time and they're moving fast enough, SMASH, BANG, BOOM! (they collide), sending debris everywhere. But if they slowly meander toward one other, gravity can gently draw them together. They form a union, merging into a larger object. If the participants are farther apart, they might not physically interact but their gravitational encounter can pull each body off course. These objects start to cross other lanes of traffic, making more collisions likely. After millions of years, to many encounters to count have happened between these planetesimals and have cleared out much of the disk's debris. They have built up much larger — and many fewer — objects that now dominate their regions. A planetary system is reaching maturity.

7. Formation of Moons There are also theories about the way moons were formed. The current theory is that moons form in one of three ways. The oldest moons were born alongside the planets. Bits of gas and dust that didn't join to form the planets gathered on their own. Gravity attracted more and more material to these bunches and they became moons. This is the same way as planets formed. Some moons (like Mars's) were once asteroids or similar objects flying by. They were captured by the planet's gravitational pull and got stuck in orbit, orbiting around it as a moon. The third way that moons could be formed is that something Mars-size hit and pieces of the planet splashed into space. These fragments formed a ring around the planet and eventually clumped together into the moon. This is the way earth’s moon is thought to be formed.

8. The Future of Our Solar System The solar system relies on the sun, so if something happens to the sun, the future isn’t looking so good for us. The sun has existed for about 5 billion years and will be around for about 5 billion more. The sun is made mostly out of hydrogen, the simplest of atoms. The hydrogen at the center of the sun is under a lot of pressure (because the sun is big and has lots of gravity). Sometimes 4 of these atoms get stuck together forming a new atom: helium. This process is called nuclear fusion and it takes a ton of energy. This fusion is what powers the sun. Hydrogen is the sun’s fuel. Eventually the hydrogen in the core of the sun will run out and the fusion will stop. The core will then shrink under it’s own gravity and the helium atoms will begin to stick together to become carbon (3 helium atoms) and oxygen (4 helium atoms). These collisions will produce more energy than the hydrogen collisions. The extra energy will cause the core to become much hotter and the sun will swell to over 100 times it’s current size. The sun will swallow mercury and Venus. Even though the core is hotter, the surface will be colder. This will change the color from yellow to red and the sun will become a red giant. The earth will also eventually be swallowed up by the sun and even if it isn’t there is no way we can live here.

9. Future of the Solar System (continued) The fusing helium will produce a solar wind much stronger than it is today. The wind will carry away some of the outer layers of the sun forming a planetary nebula. The solar wind will strengthen as more matter is carried away from the sun. At some point, though, there will no longer be enough pressure to keep the fusion going in the core. The sun will then collapse under it’s own gravity and become much smaller. This very dense star is called a white dwarf. The white dwarf will run off energy from earlier nuclear fusions, but it won’t generate any new energy. After a few billion years this energy will run out and we will be left with a dark stellar corpse. This will be the end of the world as we know it, but the matter blown away from the sun by the solar wind will eventually become a cloud of dust similar to the one that our planet was born from. Maybe some life will form on that other planet. Note: Don’t worry, by that time humans will have figured out how not to die.

10. Formations of the Solar System Bibliography Info Livio, Mario. "Discovering Planets Beyond." Hubble Site. HubbleSite, 2010. Web. 20, January 2011. <http://hubblesite.org/hubble_discoveries/discovering_planets_beyond/how-do-planets-form>. NASA, . "Stars." NASA Science: Astrophysics. NASA, 2010. Web. 20, January 2011. <http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/>. Sykes, Mark. "How Do Moons Come in to Existence?."The Free Library By Farlex. Cengage Learning, 2009. Web. 20, January 2011. <http://www.thefreelibrary.com/How+do+moons+comes+into+existence%3F-a0198169414>. "What Will Happen To The Solar System In The Future?." The Interactive Library. EdInformatics, 1999. Web. 20, January 2011. <http://www.edinformatics.com/math_science/solar_system/future_of_solar_system.htm>. Pictures "Hands Holding Our Universe Together." Living With An Invisible Disibility. Web. 20 January 2011. <http://www.latexsens.com/ourhelpinghands.htm>. "Orion Nebula Image." NASA Science: Astrophysics. Web. 20 January 2011. <http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/>. "Space Nebula." Feature Pics. Web. 20 January 2011. <http://www.featurepics.com/selections/Starry-Backgrounds-161.htm>. "Mosaic of The Crab Nebula." NASA Images. Web. 20 January 2011. <http://www.nasaimages.org/luna/servlet/detail/NVA2~8~8~14234~114775:A-Giant-Hubble-Mosaic-of-the-Crab-N>. "Earth and Moon." Wall Papers In This Category. Web. 20 January 2011. <http://www.searchpictures.net/space/planets_and_moons/sub2.html>. The Publishing Spot. Web. 20 January 2011. <http://www.thepublishingspot.com/2006/05/five_easy_questions_nick_mamat_1.html>. "Great Carina Nebula." Haysville Community Library. Web. 20 January 2011. <http://haysvillelibrary.wordpress.com/2009/12/04/>. "NIMBY Vela Supernova." Getting Things Done In Academia. Web. 20 January 2011. <http://eebatou.wordpress.com/category/uncategorized/>.

11. Formations of the Solar System The End