Modern astronomers believe that the sun and planets condensed out of a nebula or large cloud of gas and dust.
This idea is named the Nebular Hypothesis. It was first presented by the German philosopher Immanuel Kant in the late 1700’s.
Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris)
The Formation of the Solar System Our solar system began as a rotating gas cloud or nebula that collapsed toward its center under the influence of gravity. A condensation formed at the center, which is called a protostar. A flattened disk of matter surrounded the protostar, which begtan to shine and become a star, our sun.
The rising temperature from the sun removed the gas from the inner regions, leaving dust and larger debris
Inner planets formed from solid debris
Outer planets retained original gases
Planets established dominance in their regions of the solar system. After almost all of the remaining gas, dust, and small debris was collected by the larger objects, the solar system took on the form we recognize today.
Disk of gas, dust seen edge-on, star Beta in center (covered to reveal faint outer disk)
Solar System Composite http://www2.jpl.nasa.gov/galileo/sepo/education/nav/ss2.gif
Common Properties of Planet Orbits in Our Solar System As viewed from above, all of the planets orbit the Sun in a counterclockwise direction. The planets orbit in nearly the same plane (ecliptic). All planets except Pluto have an orbital inclination of less than 7°.
Inner Solar System http://www.nineplanets.org/overview.html
Outer Solar System http://www.nineplanets.org/overview.html
In mass, the sun represent 99% of the solar system
The smallest planet, Mercury, has a diameter of 3031 mi
Pluto, the previous smallest planet, has a diameter of 1457 mi
The largest planet, Jupiter, has a diameter of 88,700 mi
Earth = 7926 mi
Ganymede, the largest moon of Jupiter, is larger than Mercury, yet Ganymede is not considered a planet because it revolves around Jupiter
Two Basic Groups of Planets TERRESTRIAL (earth-like) Small size, low Mass Higher density Mostly rock Mercury, Venus, Earth, Mars JOVIAN (Jupiter-like) Large size, massive Low density Mostly gas Jupiter, Saturn, Uranus, Neptune
Classical —Known since prehistoric times, visible to the unaided eye: Mercury, Venus, Mars, Jupiter, Saturn
Modern —Discovered in modern times, visible only with telescopes: Uranus, Neptune, (Pluto)
Classification Table Planet Rocky or Gas? Small or Giant? Inner or Outer? Inferior or Superior? Classical or Modern? Mercury R S I I C Venus R S I I C Earth R S I N/A ? Mars R S I S C Jupiter G G O S C Saturn G G O S C Uranus G G O S M Neptune G G O S M Pluto ? S O S M