Theory of Intelligent Design, the best explanation of Origins

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Theory of Intelligent Design, the best explanation of Origins » Astronomy & Cosmology and God » Fine-tuning of the solar system

Fine-tuning of the solar system

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1 Fine-tuning of the solar system on Wed 7 Jun 2017 - 14:02


Fine-tuning of the solar system

The earth's habitable zone 1
The temperature of a planet is dependent on the orbital distance of the planet from the central warming star. In our own Solar System, the planets Mercury and Venus orbit too near the Sun to support liquid water: water could only exist as vapour, whereas Mars is now too cold for liquid water. The Earth lies within those two orbits, with surface temperatures allowing the continual presence of liquid water. There is a similar orbital range around all stars within which liquid water could exist on a planet. This band is called the habitable zone. Combining the two habitable zone requirements — around a star and also around the galactic center — places severe restrictions on the number of habitable planets in a galaxy. mass-extinction of complex life.

The size of the habitable zone clearly depends on the luminosity of the star, which determines the equilibrium temperature of the planet. However, modern models for the range of the habitable zone take into account more subtle effects, such as the effect of the carbonate-silicate cycle in regulating carbon dioxide in a planet's atmosphere.

The mere fact that 95% of all stars are less massive than the sun makes our planetary system quite rare. Less massive stars are important because they are much more common than more massive ones. For stars less massive than the sun, the habitable zones are located farther inward. The most common stars in our galaxy are classified as M stars; they have only 10% of the mass of the sun. Such stars are far less luminous than our sun,
and any planets orbiting them would have to be very close to stay warm enough to allow the existence of liquid water on the surface. However, there is danger in orbiting too close to any celestial body. As planets get closer to a star (or moons to a planet), the gravitational tidal effects from the star induce synchronous rotation, wherein the planet spins on its axis only once each time it orbits the star. Thus the same side of the planet always faces the star. (Such tidal locking keeps one side of the Moon facing Earth at all times.) This synchronous rotation leads to extreme cold on the dark side of a planet and freezes out the atmosphere. It is possible that with a very thick atmosphere, and with little day/night variation, a planet might escape this fate, but unless their atmospheres are exceedingly rich in CO2, planets close to low-mass stars are not likely to be habitable because of atmospheric freeze-out. We can thus look at various stars in our Milky Way galaxy and ask whether they are appropriate places for life or, indeed, have habitable zones at all. For example, could there be habitable planets orbiting binary stars or multiple star systems, places where two or more stars are locked in a complex orbital dance? Can planets with stable orbits and relatively constant regimes of temperature be found in such settings? Can planets even form in such settings? These questions are highly relevant to understanding the frequency of life beyond Earth because approximately two-thirds of solar-type stars in the solar neighborhood are members of binary or multiple star systems. Astrobiologist Alan Hale, who has written on the problems of habitability in binary or multiple star systems, notes, “The effects of nearby stellar companions on the habitability of planetary environments must be considered in estimating the number of potentially life-bearing planets within the Galaxy.”

Like a planet revolving around a star, we maintain roughly the same distance from the galactic center, and this is fortunate. Our star—by chance—is located in the “habitable zone” of the galaxy. We suspect that the inner margins of this galactic habitable zone (GHZ) are defined by the high density of stars, the dangerous supernovae, and the energy sources found in the central region of our galaxy, whereas the outer regions of habitability are dictated by something quite different: not the flux of energy, but the type of matter to found.

The most important factor affecting the surface temperature of the earth is obviously the distance from the sun. 4  If the earth were moved a few million miles closer to the sun, the surface of the earth would become warmer causing our glaciers to melt. With a decrease in the area of ice the total reflectivity of our planet's surface would thereby decrease and more of the sun's heat would be absorbed. The melting of glaciers would produce a rise of sea level, and, apart from flooding most of our modern cities, would create a larger total ocean surface area. Since seawater absorbs larger amounts of solar radiation than equal area land masses, heating of the earth would again be promoted. Furthermore, after increasing the temperature of the oceans, much of the ocean's dissolved carbon dioxide would be added to the atmosphere along with large amounts of water due to increased evaporation. The increased carbon dioxide and water vapor level of the atmosphere would again bring about a significant temperature rise. All things considered, a minor decrease in the sun's distance would have a drastic heating effect on the earth's surface.

What would happen if the earth were a few million miles farther from the sun? The reverse of the previous situation applies. We would have more of our planet covered by ice, with associated increased reflectivity of the sun's heat. The ocean would cover less of the earth's surface and the important process of absorption of heat by seawater would be decreased. Since the ocean would be colder, evaporation would be less with less heat-trapping water vapor in the atmosphere. Much of the carbon dioxide from the atmosphere would become dissolved in the colder ocean. Calculations show that a decrease of carbon dioxide in the air to just one-half of its present level would lower the average temperature of the earth's surface by about 7.0 degrees Fahrenheit! Thus, increasing the sun's distance would have a profound cooling effect on our planet.

From this discussion, we see that the earth is just the proper distance from the sun to maintain the right surface temperature suitable for life and the many important geologic processes!

A Just-Right Sister Planet 2
Jupiter is the just-right size, the just-right distance from Earth, the just-right mass and is in the just-right location to shield Earth from being regularly bombarded with comets and asteroids that would be deadly to life.
Jupiter is 40 light minutes away from Earth (i.e., it takes 40 minutes for light emanating from Jupiter to reach Earth) and Jupiter is so massive it could hold 100 planets the size of Earth. It also outweighs the combined total all of the other planets in the entire solar system by 2 ½ times. Scientists estimate that without Jupiter being the size it is and positioned where it is, comets and asteroids would strike Earth a thousand times more often than they do. One large impact or several smaller impacts would kill off all advanced life on Earth because the dust and debris ejected into the atmosphere by the impacts would prevent too much of the sun’s light and heat from reaching the surface of the earth. Without sufficient light and heat, Earth would get too cold to support life. However, if Jupiter were any larger or closer to Earth than it is, Jupiter’s gravitational force would pull Earth out of its stable orbit around the sun which would subject Earth to deadly temperature variations, unstable atmospheres, high velocity winds and a host of other problems associated with unstable orbits, all of which would be deadly to life on Earth.

Stephen Hawking has said that a collision with a comet or asteroid greater than twenty kilometers in diameter would result in the mass-extinction of complex life. It is now believed that the gravity of massive Jupiter and Saturn located outside the orbit of the Earth acts to catch many asteroids and comets entering the Solar System before they can collide with the Earth. As an example, the comet Shoemaker-Levy 9 was observed colliding with Jupiter in 1994, leaving a scar on its surface. 1 The Earth is completely and perfectly middling: it lies in the narrow habitable zone. The Earth is not the biggest, it's not the smallest. It's not the hottest, it's not the coldest. It lies in a relatively safe planetary system where nothing very exciting ever happens, no planetary collisions or extinction-level asteroid strikes. At first glance, nothing about the Earth appears to be remarkable — apart from the fact that it is the only place in the universe that we know of where life exists. Ironically, it is the perfect mediocrity of the Earth which makes it special.

1. HIDDEN IN PLAIN SIGHT - The Fine-Tuned Universe, page 47
3. RARE EARTH Why Complex Life Is Uncommon in the Universe,  Peter D. Ward - Donald Brownlee, page 53

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