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Originally Posted by Loniat
I don't think our sun was formed after a supernova.
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I think he meant our Sun was born from supernova remnants. It has to. The composition of the inner terrestrial planets contains heavy elements: Carbon, Lead, Uranium, Copper, Silver, Gold...etc. From The Big Bang, after initial expansion and cooling, the universe started with only elements of hydrogen and helium and perhaps trace amounts of lithium. So where did all the metals come from? Just a note of nomenclature, we astronomers pretty much call any elements heavier than helium "metals", because the total mass of all elements above metals in the universe is tiny compared to the mass portions made up by hydrogen and helium, so we conveniently call the rest "metals". Anyways, supernovas are the only natural process that can input enough energy to create heavy elements above iron
and spread them into the interstellar medium. The planets and our Sun are formed from the same blob of space gas and dust with heavy metals, and those heavy metals were expelled from supernovas, however many generations it may be before the whims of gravity destined the creation of our Solar System. Imagine, all the carbon atom in your body were once made in the burning furnace of stars some billions of years ago. You can wondrously and accurately say, "we are all made of stardust".
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Originally Posted by C.A.
It didn't have enough mass to have a gravity strong enough to compact itself into a 'ball'. So it formed numerous lumps instead and got dispersed by the gravitational forces of Mars and Jupiter.
One thing that supports the theory of not having enough mass, is that the combined mass of all the asteriods would make up only 4% of the Earth's moon, with Ceres itself making 1/4 of the total mass.(Mass info taken from Wikipedia)
With such a small amount of mass, it can't form anything, or couldn't have existed as a single object of such size. The gravitational forces between Mars and Jupiter simply wouldn't allow it to form anything.
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Allow me to delve deeper and correct a few misconceptions. *Digging up old astronomy lecture notes, again* First, if all the asteriods in the asteriod belt were compressed, it would form an object about or less than 2000 kilometers in diameter. There are moons that have a smaller diameter than this. The moon of Mimas is about the mininum mass limit in which its gravity is sufficient to compress itself into a spherical shape. So if the asteriods altogether can form an object 2000 kilometers in diameter, considering its density, it should have more than enough mass to "compact itself into a ball". For concrete numbers, the mass of Mimas is 3.70x10^19 kilograms. The mass of the Moon is 7.349x10^22 kg. And the asteriod's mass, 4% of that, as you said, is 2.938x10^21 kg, which is far larger than Mimas. So what prevented them from forming anything? Answer and part two:
orbital resonances.
Orbital resonances occur whenever two objects line up together periodically. When the objects are in alignment with each other at such times, gravity tugs at the objects in the same way. The effect can build up over time, and this tends to move/clear objects at such resonances. Objects that will line up, and hence have an orbital resonance, whenever an object's period is a simple ratio of another, such as 1/2, 1/3, 2/5...etc. Think about it as an analogy to music. If a tuning fork rings at a set frequency next to a piano, the strings that ring in full, half, or even quarter ratio of the tuning fork's frequency will also begin to vibrate. The formation of the asteroid belt is due to the orbital resonances that occur between Jupiter and left over planetesimals from the beginning of the formation of the Solar System. At distances in which the asteriod periods are simple ratios of Jupiter's, there are clear gaps in number distribution. For example, any asteriod at a distance (about 3.3 AU, or 4.937x10^8 km) that has an orbital period of 6 years, half of Jupiter's 12, would recieve the same gravitational nudge every 12 years from Jupiter and this nudge would eventually push the asteriods out of this orbit. It is because of these orbital resonance disturbances that prevented the asteriods from clumping together and forming a spherical object. And Mars is a nonplayer regarding this. Jupiter's mass dominates the rest of the planets, and thus its gravity also dominates the rest of the Solar System other than the Sun. The gravitational contributions from the other planets are negligable compared to Jupiter's. Here is a diagram of the asteriod belt distribution that I scanned, courtesy of
The Cosmic Perspective (pg. 371).