The most successful model of the origin of the solar system is called the nebular hypothesis. The solar system formed from a cloud of interstellar material called the solar nebula.
Solar Nebula and Its Evolution
the chemical composition of the solar nebula by mass was 98% hydrogen and helium and 2% heavier elements.
nebula flattened into a disk which all the material orbited the center in the same direction
how did the four terestial planets form
formed from the accretion of dust particles into planetesimals then into larger protoplanets
what is the core accretion model
the four jovian planets began as rocky protoplanetary cores, similar in character to the terrestrial planets. gas then accreted in a runaway fashion
alternative disk instability model
the jovian planets formed directly frmt he gases of the solar nebula. in this model the cores formed from planetesimals falling into the planets.
how was the sun formed
gravitational contraction of the center of the nebula. after 10^8 years temperatures at the protosuns center became high enough to ignite nuclear reactions that convert hydrogen into helium thus forming a true star
how have most planets been detected
atronomers have detected the "wobble" of stars around which they orbit
looks for the rare situation in which planet comes between us and its parent star called a transit
benefits of transit method
-know the true mass of the orbiting planet
-amount by which the star is dimmed during the transit depends on how large the planet is and tells diameter
-the transit the star's light passes through the planet's atmosphere aklows us to determine composition of the planet
-possible to detect a light dimming when the planet goes behind the star measures the amount of radiation which tells us the planet's surface temperature
if a star drifts through the line of sight between Earth and a more distant star the closer star's gravity acts like a lens that focuses the more distant star