Monday, April 16, 2018

Solar System - How was it created?



- 2061  - Our Solar System  -  How was it created?  It all started with a cloud of dust and gas coalescing around the Sun some 5 billion years ago.  After the rocky planets formed there was a 300 million year bombardment of asteroids that brought water back to Earth.  Of the 3,700 planets discovered most are more than 17 Earth masses, about the size of Neptune.    Most are gas planets that orbit close to their stars.
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-----------------------------  2061  - Our Solar System  -  How was it created?
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-  It all started with a cloud of dust and gas coalescing around the Sun some 5 billion years ago.  Substances near the Sun were vaporized, water and ice turned into gas leaving the cores that were the rocky planets behind.  Vaporized water formed into ice further out from the Sun where the gas giant planets formed. 
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-   After the rocky planets formed there was a 300 million year bombardment of asteroids that brought water back to Earth.  This same bombardment pockmarked the face of Mercury , the Moon , and many other airless objects.  This bombardment ended some 3,800 million years ago, although some asteroids are still entering the inner solar system.  One in particular 66 million years ago impacted Earth and killed off the dinosaurs that were living here. 
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-  During the early planet formations planets likely bounced around like billiard balls before settling into their current circular orbits.  Our particular Solar System seems unique.  When the Kepler telescope was launched in 2009 there were only a hundred exoplanets discovered.  Now there are thousands of exoplanets being studied. 
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-  Most of these exoplanets are 1 to 10 times Earth's radius and are close to their stars having orbit periods of 120 days or less.  Of the 3,700 planets discovered most are more than 17 Earth masses, about the size of Neptune.    Most discoveries are gas planets orbiting close to their stars. 
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-  The first exoplanet discovery in 1995 was Pegasi b.  It is half Jupiter mass orbiting only 4,800,000 miles from its star taking only 4.2 days.  The planet Mercury takes 88 days and is 29,000,000 from the Sun. 
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-  There is a bias in planet finding that must be recognized.  We will tend to find planets with short periods and with high masses.   An alien astronomer observing our solar system would have to wait 24 years to see two Jupiter orbits.  
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-  How to explain our solar system?  The existence of Pluto in the orbit we see means it had to somehow be pushed into that place.   The Dwarf Planet Ceres did not form where it is either?  This evidence points to planets migrating in order to get to their current orbits.   
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-  Computer models have Jupiter forming first followed by Saturn then Uranus and Neptune.  Jupiter started only 3.5 AU from the Sun  (one AU is today's Earth-Sun distance, 93,000,000 miles).  The large tail of material in its orbit slowed Jupiter's momentum.  Saturn formed at 4.5 AU.  Jupiter migrated inward until it reached 1.5 AU.   There Jupiter and Saturn reached a mean motion resonance.  Saturn making 2 orbits for every 3 Jupiter orbits.  This resonance created a braking effect. 
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-  The material orbiting inside Jupiter's orbit created an outward force causing the giant planets to move outward.  The remaining plantesimals formed a ring around the Sun where the four inner planets are today.  As Jupiter and Saturn tacked outward they captured Uranus and Neptune in resonance as well.  Uranus and Neptune exchanged enough angular momentum for them to switch places with the Kuiper Belt of asteroids.  This also had the effect of sending some asteroids inward toward the Sun and the rocky planets.
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-  Is there another planet beyond the Kuiper Belt?  In 2003 the Dwarf Planet Sedna was discovered with an elongated orbit.  Sedna is 600 miles diameter and 76 AU from the Sun. Five other objects have been found since with similar orbits. Is his an indication that there is a Planet Nine outside these orbits and yet to be discovered?
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-  Our Solar System appears to be rare compared to exoplanets systems discovered do far.  But, just because our solar system is hard to model mathematically doesn't mean that it can't happen.  Any general pattern needs some exceptions.  Maybe we are just the exception?  God only knows.
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 -------------------------   Monday, April 16, 2018   --------------------------------
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