Download The Formation of the Solar System

The Formation of the Solar System
Physics 100
Overview :
[All theories about the solar system’s formation are only theories; they are subject to change with the introduction
of new evidence]
*Our solar system formed 4.6 billion years ago when a giant supernova caused the compression of a molecular
cloud that resulted in the formation of a solar nebula.
- Supernova: exploding / dying star
- Molecular cloud: very dense gas and dust cloud
*When gravity pulled the gas and the dust together, the whole cloud began to spin, with the center having a high
angular velocity and the outer parts spinning in a ring around the dense center.
*The center of the cloud eventually collapsed together into a protostar that would eventually become the sun.
The excess material made up the protoplanetary disc that revolved in a ring around the forming sun.
- protostar: the spinning center of the cloud. After 50 million years, the protostar underwent
thermonuclear fusion and grew until it reached hydrostatic equilibrium and became the sun that we
recognize today.
- protoplanetary disc: the revolving ring of excess material that, over time, accumulated together to form
the planets, moons, and asteroids
*During the protostar’s transition into our current sun, the center of the cloud was incredibly hot, and only rocky
non-gaseous materials could withstand the heat. This accounts for the division between the inner rocky planets
and the outer gas and ice planets.
[Link to the video shown in class: http://www.youtube.com/watch?v=-ht2yzscaDc]
Mercury
*Mercury has an extremely dense metallic core. The currently visible crust is actually the result of a lava flow that
resulted from repeated asteroid bombardment. Mercury is very stable and will not change for centuries.
Planetary Motion
*The planets in our solar system all began in the protoplanetary disc that circled the sun. The planets have kept
the original motion and rotation of which they were formed.
*The cloud’s rotation (angular momentum) remains unchanged due to The Law of Conservation of Momentum.
[Link to second video shown in class: http://www.youtube.com/watch?v=V3UsrfHa4MQ]
*Venus and Uranus do not rotate in the same counter-clockwise direction as the other planets. Early collisions are
believed to be responsible for this difference.
Venus
*Venus rotates clockwise. The reason for this may involve collisions between Venus and other “mini-planets” that
still orbited the sun early in Venus’s formation. A collision between Venus and one of these mini-planets,
especially considering that the mini-planet was most likely absorbed into Venus’s body, would have altered the
angular momentum and the original spin.
Earth and the Moon
*Earth formed 4.5 billion years ago and moves in a perpendicular direction to the sun’s gravity. Earth follows
Kepler’s first law of Planetary Motion in that it travels in an ellipse with the sun as the major foci.
*It is theorized that the moon was formed after a planetary body collided with earth resulting in a fracture in the
original planet in which a piece of debris splintered off and began to orbit around the Earth. This hypothesis is
supported by similar core compositions of the Earth and the Moon, as well as similarities in mean densities.
Mars
*Mars was formed from a planetesimal (small plane) that was once part of the asteroid belt. It formed as a result
of direct accretion of grain particles , and has similar planetary compositions to Earth and Mercury.
- The asteroid belt: lies between the four terrestrial planets and the 4 gas giant planets and PLUTO. The
asteroid belt is made up of a lot of debris and material left over from the initial formation.
Uranus
*Uranus has an unusual rotation as well, and rotates 90 degrees on its side. This is also due, probably, to an
impact early in the formation process.
Pluto the Has-Been Planet
*Pluto orbits the sun in the opposite direction of the other planets, and it does not travel on the same ecliptic
plane as the other planets. Since being stripped of its “Planet” title, Pluto is now the biggest mass in the Kupier
belt.
Conclusion: The Future of the Solar System
*In 5.4 billion years, when the whole supply of hydrogen has been turned into helium, the sun will stop being a
main sequence star and become a red giant. The sun will expand in diameter and decrease in temperature, thus
irrevocably altering the composition of our solar system.