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15,000 million km; 1
AU
is the distance between the Earth and the Sun -
150 million km).
- The Sun formed from a nebula a
collapsing H/He cloud
- The inner planets are mostly rock
and metal
- The outer planets are mostly ice
and gas
- Earth's Moon formed
separately from the rest of the solar system
Atoms and molecules within the
nebula combined to form larger particles. The already present Sun
determined what kinds of atoms could persist nearby. Near to the Sun, heat
vaporized ice and prevented lightweight elements, like hydrogen and
helium, from condensing. Not the case further out however.
Earth formation
- Earth is the only planet with life -- and
ongoing plate tectonics ( the movement of the outer
surface or crust of the earth over an underlying molten mantle)
- Earth's atmosphere has more oxygen today than
it did when the planet formed
- It is likely that planets are just
a by-product of
star formation, stemming from the physical law of angular
momentum conservation. The same effect can be observed when a
spinning skater gradually pulls the arms closer to the body, thereby
turning faster and faster.
In our Solar System, the solar disk around the young Sun some 4.5
billion years ago had a mass of a few percent of the mass of the Sun and
that its radius was less than about 100 AU.
Planets are created in the swirling disk around the Sun
Planets form in this disk, most probably through
collisions, at first between dust grains and then, between
larger and larger bodies of heavy atoms and molecules now. This picture
provides a simple explanation why all planets in our Solar System not
only orbit the Sun in nearly the same plane but also all move in the
same direction. Simultaneous formation of the planets and other
small bodies around Sun is actually supported by comparing the ages of
the oldest Moon rocks and the Sun which are about the same age.
1) The centripetal forces around the spinning newly
formed sun flattens the solar disc which reaches out 100 AU
2) Bombardment of particles in the swirling disc leads to the
accretion of larger bodies of various elements that hold together
due to the force of gravity
3) Solar System has now formed the Asteroid Belt is a remnant of the
accretion disc debris
Why do the planets and moons have impact craters? Why
are they least apparent on Earth?
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