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### 33 Cards in this Set

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 In order to be considered a planet what 3 important characteristics must it meet? must have enough mass to be spherical, orbit the sun and "clear its neighborhood" how are the distances from each planet known? By Kepler's law we can estimate the distance between planets according to its orbit speed. How are planet's sizes determined in the sky? By using angular measurements in the sky and using geometry with Earth's distances to determine the sizes. What is the equation to determine a planet's diameter? D= 2dA pi / 360 degrees How is a planet's mass determined? By observing the gravitational behavior of its orbiting moons and nearby planets. How is a planet's density determined? Mass / Volume Planets orbit the sun (as viewed from the North pole) COUNTER CLOCKWISE All planets with the exception of ________________ roughly orbit sun in the same plane. Mercury and Pluto Terrestrial planets -distance to sun - masses and sizes -surfaces -densities -rotation -magnetic field -rings -moons closer to the sun smaller than jovian rockier and solid surfaces higher densities Smaller magnetic fields No rings few moons (Earth=1 Mars=2) Jovian planets -distance to sun - masses and sizes -surfaces -densities -rotation -magnetic field -rings -moons farmer from the sun larger than terrestrial Gaseous surfaces lower density faster rotation larger magnetic field many rings many moons What is a comet? What are some of its chemical components? A dirty snowball. Methane, ammonia and ice, hydrogen envelope. There are two classes of comets. What are they? what is the difference? Long period comets- take about 1 million years to orbit the sun. Orbits beyond pluto. Short term comets- orbit the sun in 200 years or less. where are each class of comets believed to originate? Long term comets- oort cloud Short term comets- Kuiper belt interplanetary rocky material smaller than 100 m. Meteorite A meteorite that entered Earth's atmosphere and burned. Meteor a meteorite that has made it to the ground? meteorite what is the cause of most meteor showers? Meteor showers occur when Earth crosses the orbit of a freshly-passing comet. Meteors are rocky and made up of what two unusual elements? Nickel and iron By dating the carbon on the rock, how old do meteors appear to be? 4.5 billion years old. What are asteroids? Rocks with sizes larger than 100 m. Where do most asteroids accumulate? The asteroid belt between Mars and Jupiter. Asteroids are made up of what elements? Iron and carbon (recall meteorites have nickel). Why are all those asteroids there? Its all jupiter's fault. It’s all Jupiter’s fault….. Because it is believed that Jupiter’s massive gravitational pull is playing tug of war with the Sun NOT allowing the asteroids to form a planet. the theory that proposes that the solar system began from dust and gas? Nebular theory How does nebular theory suppose that the cloud of gas contracts? According to its own gravity particles are attracted to the center of mass and the cloud constricts. According to the theory the planets spun quickly as they constricted creating a dense system. How does it explain how this happened? Conservation of angular momentum. As the gas constricted the angle of rotation got smaller so the velocity goes up. What shape occurs as a result of this gravitational force and conservation of angular momentum? A pancake shape (which we have since seen around new stars) What is the formula for angular momentum? Mommentum= mass x radius^2 x rate of rotation. How did planets form from this flattened disk of dust and gas? CONDENSATION. condensation occured and a certain amount came together and formed a planetesimal. The rest was blown away by solar wind and formed another planetessimal. THEN What? The planetesimals over hundreds of millions of years collided and grew into planets. Why then are the jovian planets so large? because in their formation they were able to sweep up massive amounts of gas as well. why are the inner planets composed of rocky material while the outer planets picked up gasses? TEMPERATURE. The type of material that was able to condense out depends on the temperature. Far from the sun only gas was able to condense and so the Jovian planets condensed as gases.... How many extrasolar planets have been detected? How? 193. They are detected by observing the gravitational wobble of stars because of other planets.