Astronomy- Ch. 8 – Flashcards

a. Patterns of motion among large bodies- Sun, planets, large moons rotate in an organized way (co-planar)—nearly circular orbits in the same direction (coplanar and prograde) b. Two major types of planets- terrestrial vs. jovian planets c. Asteroids and comets- locations, orbits, and compositions follow distinct patterns—Asteroids are b/t Mars and Jupiter in the asteroid belt. Also located in the Kuiper belt and Oort Cloud d. Exceptions to the rules- Earth is inner planet with large moon, Uranus is only side tilted axis, etc.

The nebular theory is a modification of the nebular hypothesis which said that the solar system formed from the gravitational collapse of an interstellar cloud of gas. It was formed when scientists used more sophisticated models of the processes that occur in a collapsing cloud of gas. It became a theory because it offered natural explanations for all four of the general features of the solar system (listed in question 1). It is so widely accepted because it successfully predicted the existence of other planetary systems (that we are found recently).

The solar nebula is the cloud of gas from which our solar system was born when it collapsed under its own gravity. By using the compositions of the Sun, other stars, and interstellar gas clouds, we know that the solar nebula contained 98% hydrogen and helium and only 2% of all other elements combined. This came from the billion of years of galactic recycling that occurred before the Sun and planets were born.

The solar nebula took the form of a spinning disk, instead of a sphere, because of three main processes: heating, spinning, and flattening. -Heating: means that the temperature increased as it collapsed representing energy conservation. As it shrank, the PE was converted into the KE of individual gas particles falling inward. These crashed into each other, converting their inward, falling KE into the random motions of thermal energy. The Sun formed in the center, where temperatures and densities were the highest. -Spinning: Like an ice skater, the solar nebula became faster as it shrank in radius representing conservation of angular momentum. Before the collapse, the rotation was very slow, but as it shrank, fast rotation was inevitable. It helped ensure that everything in the nebula didn't crash into the center because the greater the angular momentum, the more spread out it would be. -Flattening: consequence of collisions between particles in a spinning cloud. Randomly shaped and sized clumps of gas collide and merge as the cloud collapses and each clump gets the average velocity of the clumps that formed it. Basically, it becomes more orderly as the cloud collapses. The observational evidence supporting this scenario include the infrared radiation we've detected from many nebulae where star systems appear to be forming. Also, other stars have flattened, spinning disks. Other support comes from computer simulations. Also, we see other examples (like the Milky Way, planetary rings, and accretion disks of neutron stars and black holes) of where flattening should occur because of the orbiting particles colliding.

Hydrogen and helium: 98% of solar nebula. NEVER CONDENSE Hydrogen compounds (1.4% of solar nebula. Condense into ices below 150K .these include water, methane, and ammonia Rock: 0.4% of solar nebula, Condenses into solid bits of mineral b/t 500-1300K Metal: 0.2% of solar nebula. Condense into solid form at temps b/t 1000-1600K ---The ingredients present in terrestrial planets include rocks and metals because it is hotter closer to the sun where the rocks and metals could condense to form a planet. Farther away from the sun where it requires less temperature to condense hydrogen and helium and hydrogen compounds are where the jovian planets formed. In comets and asteroids, it is carbon-rich minerals that condensed because of the low enough temperature.

The frost line in the solar nebula lies between Mars and Jupiter. It is the distance where it was cold enough for hydrogen compounds to condense into ices. Temperature differences led to the formation of two distinct types of planets (terrestrial and jovian) b/c of the temperature at which the materials that make up each type of planet could condense. (Ex. Takes a higher temp to condense rock and metal [terrestrial] and a lower temp to condense hydrogen, helium, and hydrogen compounds [jovian]). This also tells us why the jovian planets are so much larger than the terrestrials (b/c hydrogen is most abundant and could only condense farther out from the Sun).

The process by which terrestrial planets formed is called accretion. It begins with the microscopic solid particles that condensed from the solar nebula's gas. Because the particles orbited the Sun just like the gas that orbited, the particles "collisions" were really just gentle touches- sticking together through electrostatic forces (static electricity). Small particles became larger ones; then, gravity began helping the process of sticking together, which made the growth much faster. These particles became planetesimals ("pieces of planets"). Only the largest planetesimals avoided being shattered and could grow into terrestrial planets.

Condensation of ices farther out in the solar nebula meant there were more solid materials in addition to the metal and rock. Jovian planets formed as gravity drew gas around ice-rich planetesimals much larger than Earth; (when it gets about 10 Earth masses) therefore they had a strong enough gravity that it could capture and hold hydrogen and helium that made up a vast majority of the material in the solar nebula. After collecting and collecting, they hardly resembled the icy seeds from which they grew.

...

...

...

...

...

...

...

...

...

...

...