No general astronomy class could be complete without discussing how the Sun, the

Question

No general astronomy class could be complete without discussing how the Sun, the Earth and the other planets form and came to be in the arrangement that we observe today in our Solar System Present, explain, and justify the currently accepted model of the formation of the Sun and Solar System (in particular), as well as other stars and planetary systems in general. How does that model address the patterns of physical evidence in the Solar System? Briefly discuss the results from missions searching for extrasolar planets, such as Kepler.

Explanation / Answer

In general the theories of orign of the solar system ca be divided in two groups

1)Evolutionary theory: this theories re suggest that planets are frmed during the evolution of the sun.

eg : Nebular hypothesis

2) catastropic theory: these theories are which imagine that planets are formed by some accident or catastrophe such as the cose approach of two stars or collision of two stars.

eg: planetesmal,gaseous tidal hypothesis

best known hypothesis for the origin of solar system are as follows

1)Nebular hypothesis

2)Planetsimal hypothesis

3)Gaseous tidal hypothesis

4)Binary star hypothesis

5)Gas dust cloud hypothesis

The most widely accepted theory of planetary formation, known as the nebular hypothesis, maintains that 4.6 billion years ago, the Solar System formed from the gravitational collapse of a giant molecular cloud which was light years across. Several stars, including the Sun, formed within the collapsing cloud. The gas that formed the Solar System was slightly more massive than the Sun itself. Most of the mass collected in the centre, forming the Sun; the rest of the mass flattened into a protoplanetary disc, out of which the planets and other bodies in the Solar System formed.

CURRENTLY ACCEPTED MODEL:Just as the Sun and planets were born, so they will eventually die. As the Sun begins to age, it will cool and bloat outward to many times its current diameter, becoming a red giant, before casting off its outer layers (forming what is misleadingly called a planetary nebula) and becoming a stellar corpse known as a white dwarf. The planets will follow the Sun's course; some will be destroyed, others will be ejected into interstellar space, but ultimately, given enough time, the Sun's retinue will disappear.

There are, however, arguments against this hypothesis.

physical properties of solar system:

1)Except for pluto ,the plantery orbits lie in close to the samme plane,which contains the sun and orbit of the earth

2)the planets revolve %about the sun in the sam sense,which is counter clockwise when veiwe from above he ecliptic plane(prograde)

3)the rotation of the planets about their own axis are also prograde except venus(retrograde - clockwise); uranus,whose axis of rotation lies nearly in the plane of of its orbit;and pluto ,whose rotation axis and obital plane are oblique to ecliptic.

4) each planet is roughly twice as far from the sun as its closest neighbour.

5) the compostion of the planets are two groups :terristial planets close to the sun ,small size and denser & great planets far from the sun,large in size and less denser

6)the sun has almost 99% of the mass of the solar system,but the planets account for more than 99% oof the angular momentum

extra bodies:The first white dwarf discovered was in the triple star system of 40 Eridani, which contains the relatively bright main sequence star 40 Eridani A, orbited at a distance by the closerbinary system of the white dwarf 40 Eridani B and the main sequence red dwarf 40 Eridani C.

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