Far out cosmology: Our solar system special? (Introduction)

by David Turell , Friday, April 01, 2016, 20:09 (2940 days ago) @ David Turell

this article covers the theory of solar system formation. Ours turns out to have a special ingredient:-http://phys.org/news/2016-04-earthsthe-chemistry-star-planet-formation.html-"A "solar system" like planetary system has at least one Earth-like planet at approximately 1 astronomical unit (AU) from the star - where more ideal conditions for life can develop - and at least one ice giant like Jupiter at 3-5 AU in order to keep away comets from the Earth-like planet. In our galaxy alone, there are around 10 billion stars and at least 10 million planets. For those stars similar to our sun, there exist over 4 million planetary systems similar to our solar system, with the closest Earth-like planet at 20 light years away.-***-"How does an Earth and a Jupiter form at their ideal distances from a star? Let's take a closer look at how stars and planets are created - via the astrochemical cycle. Essentially, dense clouds of gas and dust become so opaque and cold that they collapse into a disk. The disk, rotating around a to-be star, begins to transport mass in toward the center and angular momentum outward. Then, approximately 1% of the star mass is left over from the process, which is enough to form planets. This is also why planets around stars are ubiquitous.-"How are the planets formed? The dust grains unused by the star collide and grow, forming larger particles at specific distances from the star - called snowlines - where water vapor turns into ice and solidifies. These "dust bunnies" grow into planetesimals (~10-50 km diameter), such as asteroids and comets. If the force of gravity is large enough, the planetesimals increase further in size to form oligarchs (~0.1-10 times the mass of the Earth), that then become the large planets of the solar system.-"In our solar system, a process called dynamic reorganization occurred that restructured the order of our planets, putting Uranus before Neptune. This means that if other solar systems did not undergo such dynamic reorganization at an early point in formation of solar system, then other Earths may have lower organic and water content than our Earth. In that case, what constraints do we need to apply to determine if a water/organic delivery mechanism exists for exo-Earths? Although we do not currently have the scientific knowledge to answer this, with ALMA and the next generation of optical/IR telescopes, we will be able image the birth of solar systems directly and better understand how our universe came to be.-Comment: In bold is the theory of how planets switched positions, which helped Earth become so safe:-http://www.swri.org/4org/d15/planetsci/moon.htm-"In this model, the giant planets — Jupiter, Saturn, Uranus and Neptune — formed in a much more compact configuration than they have today. Just outside their orbits loomed a massive disk of comets. Gravitational interactions between the planets and the comet disk caused the planets to slowly migrate in space. Computer simulations indicate that, after hundreds of millions of years, Jupiter and Saturn reached orbits where their mutual gravitational kicks became quite pronounced. This triggered an instability that led to a violent reorganization of the outer solar system. Uranus and Neptune were pushed into the comet disk, scattering its members throughout the solar system. Some of these scattered objects then struck, or "bombarded," the planets and moons of the inner solar system."-Further comment: We still look very special.