where and how is a planet formed?
209423
Some massive stars don't just fuse hydrogen into helium to burn. By the process of nuclear fusion the most massive stars will continue to fuse helium, lithium and even heavier elements in the periodic table as high as iron before they go super nova. When these stars go super nova even heavier elements such as Uranium can be formed.\nThe resulting nebula from the super nova will be rich some elements required to make rocky planets such as our own.\nPlanets are formed around stars in much the same way as stars . . . by gravity.\nNebula's can be quite lumpy. The more dense bits will, by the force of gravity, attract more matter, and become more dense, thus attract even more matter and so on.\nThis process will always end up with matter starting to spin. The Star that is forming in the middle will be surrounded by a spinning disc of gas and dust. This is called the accretion disc.\nThe accretion disc is also lumpy and the same process that forms the star also takes place, however as there is a lot less matter, these lumps rarely reach the pressures and temperatures required to start nuclear fusion and form stars, and so they condense into rocky planets, asteroid, or gas giants, depending on the composition of the matter that was there to start with.\nWhen there is enough matter in the accretion disc a binary star system is often formed.\nOne interesting fact is that if our solar systems Jupiter was four times more massive it would likely have been another smaller star.\nHope this helps!!!
181404
big bang didnt produced planets. it produced gases and small particles. when the gases started concentrating at a point in space, they experienced huge forces of gravity. and thus got molded in a shape which offers minimum volume(SPHERE).
246558
two reasons, gravity and angular momentum.  Gravity tends to pull matter into one centralized spot, but angular momentum must be conserved.  That mass that escaped being part of the sun attracted mass to centralized locations, what became the planets, flattening things out to a disk shape
393568
A little more specifically, meteorites contain little inclusions called "chondrules" which have not been melted and reformed since they first formed in the proto-planetary disk around our sun.  All rocks we find on Earth or any other world have been formed since that time; the "fingerprint" of what conditions were like in space before becoming part of a planet is lost. This is not the case for chondrules in meteorites.\n\nChondrules give us insight into the sorts of particles that were available for larger bodies (and eventually planets) to form from.\n\nYou can read about chondrules on wikipedia.\nhttp://en.wikipedia.org/wiki/Chondrule\n\nAsteroids are examples of the smallest gravitationally bound objects in the solar system.  These are possible building blocks of protoplanets (enough of them stick together and you can have enough gravity to start pulling dust and even gas right out of the proto-solar disk).  By understanding their characteristics, we can more accurately model the formation of protoplanets.
513511
There isn't any singular "scientific definition" of what's a planet, it's more a matter of convention and nomenclature.  So, if the astronomy community wants to call Jupiter a planet, it is, until they decide to change the definition of a planet.
240459
It is a myth....a bedtime story.  The Earth was formed over millions of years.
590743
Imagine long, long ago. There is no earth. There is no sun.\n\nThen some of the interstellar dust, which is flinging about all over the place, starts to clump together.\n\nThe gravity of the clump pulls more dust in. And more. And more.\n\nBut each new bit of dust is moving, so as it gets caught by gravity it will move into an orbit, flying round the centre of the cump - just like comets caught by the Sun do.\n\nAs more and more dust collects it ends up as a spinning blob because of this. Because the blod is spinning then centrifugal force (I know, its a fictitious force) throws it out into a disk. This is called an accretion disk.\n\nWhen the blob in the middle gets big enough it becomes the sun. And in the disk some of the same happens to form the planets. Which are of course spinning as you can see.
518268
The planets all condensed from the same dust cloud. This cloud was in orbit around the sun and was rotating. As a result of the rotation it was spun out into a disk - this is called an accretion disk and is seen around a lot of stars. So all of the planets condensed out of a disk and hence are in the same plane.\n\nSome objects orbiting the sun did not condense from this disk but were captured. These are typically not in the plane of the ecliptic. Pluto - recently removed from the canon of planets - is in this category.
392687
The International Astronomical Union decided that Pluto was no longer a planet.  Instead, they decided to classify it as a "dwarf planet".\n\nSee the details below.\n\nRESOLUTION 5A\nThe IAU therefore resolves that "planets" and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:\n\n(1) A "planet" [footnote 1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.\n\n(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [footnote 2] , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.\n\n(3) All other objects [footnote 3] except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".\n\n\nFootnote 1: The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.\n\nFootnote 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.\n\nFootnote 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.\n\nRESOLUTION 6A\nThe IAU further resolves:\n\nPluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
595062
Planets are constantly moving and changing.  Magnetic fields and brightness, reversing rotations, varying atmospheres, geography, etc.  Both position and composition of each planet changing over millions of years will move them further away or ever closer to each other and it is possible that conditions may be available for new life to form and grow.
19196
GREAT QUESTION!!!!\n\nThe Kuiper Belt is the "leftovers" from when the Solar System was formed. It exists out past the orbit of Neptune.\n When our Solar System was forming out of an interstellar cloud, most of the matter was gravitationally pulled to the center. This caused the center to heat up until fusion began and our Sun was born. What was left behind began spinning around the new Sun and eventually became the nine planets, asteroids, and moons that make up our stellar home. \n There is an Asteroid Belt between Mars and Jupiter that is made up of mainly rocky objects, but this is not the Kuiper Belt. As the Sun became hotter and hotter, it actually "melted * " all of the ice in the inner Solar system and pushed it out to the outer solar system along with most of the excess gas and dust left over from the Sun's creation. What was left in the inner Solar System was the rocky-- or terrestrial(Earth-like)-- planets of Mercury, Venus, Earth-Moon, Mars and the Asteriod Belt. \nThe ices, and gas that was pushed out farther became the four gas giants-- or Jovian(Jupiter-like)-- planets of Jupiter, Saturn, Uranus, Neptune, and all of the icey Moons that orbit them. \nIf the theory is correct, that why Jupiter has most of the excess mass left over from the Sun's creation at that part of the Solar System. It was far enough- and cold enough away from the Sun for the ice to become solid enough again. The cooler gas, collapsed down to become mostly Jupiter at that distance from the Sun. (That's why it was such a big surprise to discover Jupiter + sized planets around other stars at distances very close to their sun.) The rest of this gas became Saturn, Uranus, and Neptune. \nFarther out than Neptune, the only things left were unmodified (not melted) ices. \nTHAT'S THE KUIPER BELT!\n It's believed to be another "asteroid belt" of sorts, but it is made up of mainly "dirty ice" which is mainly different kinds of ice and water ice with rocks and dust--think of it as dirt-- thrown in.(Astronomers can't just call something as simple as dirt, dirt, so they call it dust. Dust includes stuff like dirt, rocks, and anything else you might find in an interstellar cloud.) \n That is what Pluto and it's Moons are made of, as well as the recently discovered objects that are a little smaller than Pluto, and the one they found that is larger.\n That's why people are now questioning whether Pluto should be called a planet, because there are probably millions of these "Trans-Neptune objcts" out there waiting to be discovered. These little snowballs are of interest because they are basically undisturbed relics from before the Sun existed and can tell us quite a bit about the early Solar System, the Earth, and us!\n These ices should be different for the icy moons of Jupiter, Saturn, etc. because they weren't melted and pushed out away from the Sun. They were always far away beyond the orbit of Neptune and left undisturbed. \nStick around for the next 9 1/2 years as our Pluto spacecraft flys out there and notice all of the other discoveries of new Kuiper Belt Objects in the years before it arrives!!!\n ------------------------------------------------\n* Ice can't "melt" in the vacuum of space, so it goes straight from a solid to a gas. (We call solid water, for example, ice, and gaseous water, water vapor.)
663222
astronomers are trying to define the word planet, but it isn't easy.  many favor the reclassification of the bodies in the solar system into three groups, the rocky terrestrials, the gas giants, and the ice dwarfs.  there are hundreds of known ice dwarfs including pluto, quaoar, sedna, 2003 EL61, and 2003 UB313 (the official name of xena).  2003 UB313 is about five percent bigger than pluto.  this is called the kuiper belt.\n\nhttp://en.wikipedia.org/wiki/Kuiper_belt
270347
astronomers are trying to define the word planet, but it isn't easy.  many astronomers favor the reclassification of the bodies in the solar system into three groups, the rocky terrestrials, the gas giants, and the ice dwarfs.  there are hundreds of known ice dwarfs, including pluto, quaoar, sedna, 2003 EL61, and 2003 UB313 (the official name of xena).  this is also called the kuiper belt.  pluto was the first kuiper belt object discovered.  2003 UB313 is about five percent bigger than pluto.\n\nhttp://en.wikipedia.org/wiki/Kuiper_belt
635131
So many questions.  I'll go with what I know:\nthe universe is expanding\nstars generate energy from fusion of Hydrogen, except later in life when it's heavier elements.\nstars' death depends on the mass\nstars end life as :nova, supernova, black hole, so they must begin life as a nebula\nmassive stars become black holes or ... neutron stars/pulsars? I think\n4 terrestrial planets:\nMercury, Venus, Earth, Mars.  Earth and Mars have natual satellites.  Mercury is the smallest.  Between the inner planets & outer planets is an asteroid belt.\nThe outer planets are Jupiter, Saturn, Uranus, Neptune and Pluto.  Sometimes the path of Pluto makes it closer to the sun than Neptune.  Otherwise, I've listed them in order outward from the sun.
460536
I'm certainly no expert, but from my high school physics days I recall something about Bode's law.  You might be able to Google or Wikipedia it.  It was an explanation, in Newtonian physics terms, of why the planets are where they are.
102582
The sun is a big fire at the center of the of the solar system. The planets are balls that float around the sun. if the planet is to close to the sun nothing can live on it, It is too hot. If the planet is to far away from the sun nothing can live on it, it is too cold. On earth it is just right. Our atmosphere protects us from all the other stuff floating around. a meteorite is a rock that would hit the earth if our atmosphere did not protect us. the moon is a ball floating around a planet. Our moon is called "Luna" it has no atmosphere and lots of meteors hit it.
618256
They start out as an enormous gas cloud. Gravity causes the parcicles in the cloud to spin around the point of center mass, and the velocity of the spin subsequently flattens it into a disk. That's how galaxies, and on a much smaller scale, planetary systems form.