Solar System3

8/8/2019 Solar System3

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1. Which of the following common kitchen items is classified asbeing an acid?

A. ? Dish soap

B. ? Lemon juice

C. ? Baking soda

D. ? Eggs

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Solar System Formation
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Do the planets and moons in our solar system tend to orbit and rotate in thesame plane? If so, what would be the cause of such uniformity? Why do allthe planets orbit the Sun in the same direction?- question from Andy Johns & Tom

Yes, the planets and most other large bodies of the solar system do orbit the Sun inabout the same plane. This plane that contains the orbits of most of the planets,moons, and asteroids is called the ecliptic plane. When viewed from overhead, theplanets also rotate about the Sun in the same counter-clockwise direction. Mostmoons also rotate around their parent planets in this same direction. The reason forthese behaviors relates to how the solar system was formed some 4.6 billion yearsago. Bear in mind that the explanation we are about to discuss is only a theory thatappears to explain the structure of the solar system as scientists currentlyunderstand it. As astronomers learn more about our own solar system as well as theplanets orbiting other stars in the galaxy, it is very possible that this theory maychange and evolve.

Planets of the solar system (not to scale)

The leading hypothesis to explain how the solar system formed is called thecondensation theory, which is based on a related explanation called the nebulartheory. A nebula is a large cloud of gas and dust that exists in the depths ofinterstellar space. These clouds typically form during the death of a giant star when itgoes supernova. This mighty explosion sends most of the star's mass outward intospace as a massive wave of debris. The nebular cloud from which our solar systemformed may have accumulated from one or more stars that went supernova billionsof years ago. Astronomers have used the Hubble Space Telescope and otherobservatories to discover similar nebular clouds where new stars and possiblyplanets appear to be in the process of being created.


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Stars forming in small protrusions from the Eagle Nebula

Astronomers estimate that the nebular cloud from which our solar system formedcontained about two to three times the mass of the Sun and was about 100astronomical units (AU) across. An astronomical unit is defined as the average

distance between the Sun and Earth, or about 93 million miles (150 million km). Thismassive loosely-bound cloud of dust, ice particles, and gases (primarily hydrogenand helium) had some small rate of rotation due to the method in which it wasformed. Over time, this nebular cloud began to collapse inward. The collapse mayhave itself been triggered by a supernova that sent shockwaves through the cloudcausing it to compress. As the cloud compressed on itself, the gravitational attractionof the matter within increased and pulled the material in even further. The nebulacontinued to contract under the influence of gravity causing it to spin faster. Themore the cloud contracted, the faster it rotated due to the conservation of angularmomentum. The rate of contraction was greatest near the center of the cloud wherea dense central core began to form. As the rate of rotation of the nebula continued to

increase, centrifugal effects caused the spinning cloud to flatten into a disk with abulge at its center.


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Contracting nebular cloud increasing its rate of rotation

The middle of this spinning disk further condensed to eventually form the Sun at thecenter of the solar system. The material spinning around this new star alsocondensed into several large chunks of material called planetoids. As theseplanetoids collided, they coallesced into larger bodies to form the planets that existtoday. Because the Sun and planets all formed from the same nebular cloud, they allrotate in the same direction that was induced on the disk of material as it coallesced.Not only do the planets all rotate counter-clockwise around the Sun, but the Sun andnearly all the planets rotate counter-clockwise about their axes. The solar equatorand the plane containing the orbits of the planets are also nearly identical, furthersupporting the formation theory described above.


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Spinning cloud flattening into a disk and condensing into a star and planets

Only a few exceptions to this explanation can be found in the solar system. Theplanet Venus actually rotates clockwise around its axis in what is called a retrogrademotion. Uranus is also in an unusual orientation since the world is tilted on its sidewith its north and south poles in about the same plane as the planet's orbit aroundthe Sun. Tiny Pluto is also tilted on its side and is the only planet with an orbitconsiderably outside of the ecliptic plane. While the reasons for these eccentricitiesare unknown, it is believed that large collisions with other large bodies during theformation of the solar system may account for the unusual characteristics of theseplanets.- answer byJeff Scott, 16 October 2005

Related Topics:

I heard that some people think Pluto shouldn't be called a planet. Someonealso found a new object even bigger than Pluto that may or may not be aplanet. It's all so confusing! Can you please explain?

What are the colors of the planets?
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