How the solar system formed?
in how old are stars we found that the sun will burn hydrogen for 10 billion years. but because the sun is a field star we could not determine. how long ago the hydrogen burning started in how old is the earth moon system.
we found that the oldest solid earth and moon material was 43 billion years old. but we could not determine the age of the earth from its original start because the giant impact turned. the mantle to magma in this chapter well cover.
the age of the solar system itself which will give us both the age of the sun and the age of the earth to get a handle on the age of the solar system. well need to review planetary formation theory any such theory would need to explain. our solar system as we see it today well start with a look at some of the key characteristics of our system.
we have the sun at the center and four relatively small rocky planets in the inner solar system and four much larger gaseous planets in the outer solar system. they are all in nearly circular orbits and they are all in the same orbital plane. none of the planets are orbiting outside the plane like some comets asteroids and dwarf planets do our theory of planetary formation will need to explain these facts in our how older stars segment wave covered.
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how the circumstellar disk feeds the central object leading to the formation of proto stars tottari stars and eventually fully formed helium fusion burning stars the process from the beginning of the proto star phase to a fully fledged star is estimated to take from 1 to 200 million years. during this period the debris in the disk is forming planets in the nucleosynthesis segment of the lambda cold dark matter big bang theory chapter.
we covered the content of clouds like these for the first generation of stars. at that time it was limited to hydrogen some helium and just traces of beryllium and lithium planetary nebula form when normal stars run out of hydrogen. the violent process created pressures and temperatures large enough to fuse hydrogen and helium into heavier elements and eject them into the interstellar medium from which giant molecular clouds. like this are formed these include carbon nitrogen and oxygen along with even smaller amounts of heavier elements.
like silicon sulfur and iron but this kind of star transition does not have energy to fuse enough protons to create atoms larger than iron supernova explosions occur. when supermassive stars run out of hydrogen these seed even heavier elements into the interstellar medium like lead zirconium silver tungsten.
and gold but even at these extreme energies it is unlikely that a supernova could produce elements larger than lead. this is because of the repulsive force of light charges is so strong the coulomb force creates.
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the coulomb barrier you may recall from our last chapter on how older stars. that a proton in our sun can collide a trillion times a second with other protons and still not fuse for a billion years. but neutrons have no charge and their fusing has no such barrier.
its understood that neutron star mergers are the origin of the majority of all the heaviest elements found throughout. the universe for our collapsing cloud we know that it contained all 94 natural elements. because we find them here on earth 99 of the mass of the circumstellar disk is in the form of gas with just one percent.
in the form of dust the solid dust has little effect on the star formation but its key to planetary formation dust is the only solid grains available for growing planets dust itself cannot be formed directly from purely gaseous material at the low densities found in interstellar molecular clouds.
instead solid grains are known to form in planetary nebula supernova and in the outer atmospheres of cool supergiant stars.
the dust in the interstellar medium extinguishes light from stars by absorption and scattering. the scattering leads to emissions of their own comparing dusty clouds to nonduty clouds using spectral absorption and emission lines shows. that almost all the iron magnesium silicon much of the carbon and some of the oxygen and nitrogen are contained in the dust this makeup is similar to the terrestrial amorphous nanocrystalline rocks.
if the temperature permits they are surrounded by a mantle of water ice. the original dust grains in the cloud are no longer available for direct observation but to this day. there are similar objects in our solar system called interplanetary dust particles. they are being collected in the thermosphere by the international space station.
here’s an electron microscope view of one of them its 10 micrometers in length. that’s around 100 times larger than interstellar dust nasa also uses high flying aircraft to collect dust at high altitudes.
before it gets close enough to the surface to mix with earth elements in 2018 a team of scientists from the university of hawaii examined this dust with electron microscopes. they mapped the element distributions and discovered that these glassy grains are made up of sub grains that aggregated together prior to the formation of the comet.
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the interplanetary dust particles came from these represented samples of the early. interstellar dust is the base material for planet formation the dust grains run into each other and stick forming larger and larger grains mixing compounds and eventually forming mineralrich pebble sized objects that grow to bolder size.
the near-earth asteroid tc25 is an example of an object this size with a 4 meter diameter. that’s 13 feet its one of the smallest asteroids ever detected the process continues to grow. the rocks into rubble heaps large enough for a little gravity to hold them. together ryugu is an example of an object this size. its one kilometer wide and weighs in at just under a half a trillion kilograms.
japan landed rovers on this asteroid in 2018. you can see the rubble nature of the object with this picture taken from the surface by the time enough matter has accumulated into objects like these.
we have what astronomers call planetesimals these can extend from several to hundreds of kilometers in diameter comet 67p visited by the rosette mission in 2014. is thought to be a combination of two planetesimals that bound together in a slow speed collision.
their combined mass is just under 10 trillion kilograms this is a rokoth it was discovered in 2014. out in the Kuiper belt by the new horizons search team using the hubble space telescope. this object is 36 kilometers across thats 22 miles its considered a minor planet like pluto, like p67.
it has two lobes that collided slowly a close examination of the surface shows lighter lines separating sections of the lobe these indicate that a rockhoth was built piece by piece by the coalescing of over a dozen smaller planetesimals by the time this collide and merge process creates objects with enough mass to produce a gravitational strength that exceeds the structural strength of the rocks.
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the object is forced into a spherical shape ceres is a good example of this and once. the mass reaches around 14 billion trillion kilograms solid mass convection activates. the temperatures and pressures inside the object liquefy matter and the core becomes molten mercury our smallest planet is a good example of this.
the star Fomalhaut is a good example of this process its circumstellar disk morphed into a protoplanetary disk with at least one object large enough to be considered a planet formal help b over time these larger objects continue to grow by accumulating matter from the disk.
we find that in each region each orbit each distance from the sun everything coalesces into one massive object these larger objects sweep out the remaining debris in their orbits. this is a defining characteristic for planets all the little deviations averaged out as the smaller particles with varying elliptical orbits combined.
this explains orbits being nearly circular and all in the same plane but the actual process is very chaotic not as simple and straightforward as this illustration the process of accumulating matter in the disc into larger objects came to an end. when the sun ignited as a main sequence star and its strong solar winds blew away any remaining loose material computer model estimates for how long this process takes range from 100 million to 200 million years.
here’s a computer simulation created by Caltech that illustrates. this chaos planets interact with the rotating disk and lose momentum moving their orbits closer to the sun or gain momentum increasing their orbital distance from the sun changing orbits create collisions between planets moons form and collide with each other and with planets comets. and asteroids form and smash into everything but out of this chaos we get our current order there is an expected difference between how this works out for planets forming in the inner parts of a solar system. and how it works out for planets forming in the outer parts of the solar system in the inner parts closer to the central star.
the forming of planetesimals increased as the objects began to attract each other via gravity objects grew to planet sizes and swept out. the debris in the vicinity of their orbits the disc experienced a chaotic period of collisions. that resulted in nine major planet sized objects along with dozens of moons and millions of asteroids and comets in addition as the sun heated up.
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the snow line moved out to where we find it today just outside. the asteroid belt this line separated the four waterless inner solar system planets from the five waterish outer solar system planets. the giant impact hypothesis has a collision between the earth and a mars sized planet.
liquefying the crust of both planets and forming the moon from ejected matter based on uranium lead dating of zircon crystals found in Australia. and on the moon this happened 43 billion years ago that would be 200 million years after the original earth. formed given the mass of our sun we know that in the beginning.
it had enough hydrogen to shine for a total of 10 billion years we now figure that. it has been burning for 46 billion years. therefore we can expect that it will burn for 54 billion more years before it runs out of fuel. we started with a giant molecular cloud rotating around the milky way every 213 million years 26 000 light years from the center.
it was seated with uranium around here a little over an eighth of a revolution from our current position. it rotated an additional six and a half times before the cloud segment started to collapse. here where we find the Perseus arm today it took only half of a revolution more to form the entire solar system. today we have a beautiful planet with a sun that will sustain us for billions of years.
