Astronomy Test 2
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Four main features of planets
- 1. Patterns of motion among large bodies. The sun, planets, and large moons generally orbit and rotate in a very organized way.
- 2. Two major types of planets. The eight official planets divide clearly into two groups: the small, rocky planets that are close together and close to the sun, and the large, gas-rich planets that are farther apart and farther from the Sun.
- 3. Asteroids and comets. Between and beyond the planets, huge numbers of asteroids and comets orbit the Sun. The locations, orbits, and compositions of these asteroids and comets follow distinct patterns.
- 4. Exceptions to the rules. We find a few notable exceptions to the general patterns observed in the solar system. For example, Earth is the only inner planet with a large moon, and Uranus is the only planet with its axis essentially tipped on its side. A successful theory must make allowances for such exceptions even as it explains general rules.
Comparing the planets to each other in order to understand their similarities and differences.
What are the patterns of motion:
- 1. All planetary orbits are nearly circular and lie nearly in the same plane.
- 2. All planets orbit the Sun in the same direction: counterclockwise as viewed from high above Earth's North Pole.
- 3. Most planets rotate in the same direction in which they orbit, with fairly small axis tilts. The Sun also rotates in this same direction.
- 4. Most of the solar system's large moons exhibit similar properties in their orbits around their planets, such as orbiting in their planet's equatorial plane in the same direction that the planet rotates.
What are the two distinct planetary classes?
Terrestrial planets and Jovian Planets.
The four planets of the inner solar system: Mercury, Venus, Earth, and Mars. Relatively small and dense, with rocky surfaces and an abundance of metals in their cores. They have few moons, if any, and no rings. We count our Moon as the fifth terrestrial world, because its history has been shaped by the same processes that have shaped the terrestrial planets.
The four large planets of the outer solar system: Jupiter, Saturn, Uranus, and Neptune. Much larger in size and lower in average density than the Terrestrial planets. They have rings and numerous moons. They are made mostly of hydrogen, helium, and hydrogen compounds-compounds containg hydrogen, such as water, ammonia, and methane. Because these substances are gases under earthly conditions, the jovian planets are sometimes called gas giants.
compounds containing hydrogen, such as water, ammonia, and methane.
rocky bodies that orbit the Sun much like planets, but they are much smaller
asteroids that are between the orbits of Mars and Jupiter
small objects that orbit the Sun, but they are made largely of ices mixed with rock
The donut-shaped region beyond the orbit of Neptune. Contains at least 100,000 icy objects, of which Pluto and Eris are the largest known. Objects all orbit the Sun in the same direction as the planets, though many have moderately large inclinations to the ecliptic plane.
Cometary region which is much farther from the Sun. Its most distant comets may sometime reside nearly one-quarter of the distance to the nearest stars. Orbits are randomly inclined to the ecliptic plane, giving it a could shape that is roughly spherical.
Exceptions to the rules.
Uranus' tilt is nearly on its side and Venus rotates clockwise. While most large moons orbit their planets in the same direction as their planets rotate, many small moons have much more unusual orbits. Terrestrial planets have no moons or very small moons, except for Earth which has one of the largest moons in our solar system.
When a spacecraft goes past a world just once and then continues on its way
When a spacecraft that orbits the world it is studying, allowing longer-term study.
When a spacecraft is designed to land on a planet's surface or probe a planet's atmosphere by flying through it. Some carry rovers.
Lander or probe
Requires a spacecraft designed to return to Earth carrying a sample of the world it has studied.
Sample return mission
When satellite's use gravity to bend its path rather than by burning fuel. They essentially speed up the spacecraft significantly while slowing the planet by an unnoticeable amount
Cheaper than other missions because they are less expensive to launch into space. Offer only a relatively short period of close-up study. Carry small telescopes, cameras, and spectrographs. Can obtain higher-resolution images and spectra than even the largest current telescopes viewing these worlds from Earth because they are able to get within a few tens of thousands of kilometers or closer to other worlds. May also carry instruments to measure local magnetic field strength or to sample interplanetary dust.
Can study another world for a longer period of time than a flyby. Often carry cameras, spectrographs, and instruments for measuring the strength of magnetic fields. Some carry radar, which can be used to make precise altitude measurements of surface features. More expensive because it has to carry extra fuel to change from an interplanetary trajectory to a path that puts it into orbit around another planet. Orbiters have been to the Moon, to the planets Venus, Mars, Jupiter, and Saturn, and to two asteroids.
Landers or Probes
Most "up close and personal". Probes collect temp. pressure, composition, and radiation measurements. Landers offer close up surface views, local weather monitoring, and the ability to carry out automated experiments. Some landers carry robotic rovers able to venture across the surface.
Sample Return Missions
Experiments must be designed in advance and must fit inside the spacecraft.
Missions that combine more than on type of spacecraft. For example, the Galileo mission to Jupiter included an orbiter that studied Jupiter and its moons as well as the probe that entered Jupiter's atmosphere.
The detailed theory that describes how our solar system formed from a cloud of interstellar gas and dust.
The piece of interstellar cloud from which our own solar system formed.
What three processes altered the density, temperature, and shape of the solar nebula that changed it from a large, diffuse cloud to a much smaller spinning disk?
Heating, spinning, and flattening.
The temperature of the solar nebula increased as it collapsed. As the cloud shrank, its gravitational potential energy was converted to the kinetic energy of individual gas particles falling inward. These particles crashed into one another, converting the kinetic energy of their inward fall to the random motions of thermal energy. The sun formed in the center, where temperatures and densities were highest.
The solar nebula rotated faster and faster as it shrank in radius. The rapid rotation helped ensure that not all the material in the solar nebula collapsed into the center: The greater the angular momentum of a rotating cloud, the more spread out it will be.
The solar nebula flattened into a disk. Different clumps of gas within the cloud may be moving in random directions at random speeds. The clumps collide and merge as the cloud collapses, and each new clump has the average velocity of the clumps that formed it. The random motions of the original cloud therefore become more orderly as the cloud collapses, changing the cloud's original lumpy shape into a rotating flattened disk.
solid bits of matter from which gravity could ultimately build planets.
The general process in which solid (or liquid) particles form in a gas.
These gases never condense in interstellar space
Hydrogen and helium gas
Materials such as water, methane, and ammonia can solidify into ices at low temperatures
Gaseous at very high temperatures, but condenses into solid bits of mineral at temperatures between about 500 K and 1300 K, depending on the type
Condense into solid form at higher temperatures than rock. Are gaseous at very high temperatures. Examples: Iron, nickel, and aluminum.
Four major categories of the ingredients of the solar nebula
Hydrogen and helium gas (98%). Hydrogen compounds (1.4%). Rock (.4%). Metal (.2%).
the distance at which it was cold enough for ices to condense. lies between the present-day orbits of Mars and Jupiter.
Inside the frost line what elements could condense into solid "seeds"
metal and rock. that's why the terrestrial planets are made of metal and rock.
What elements could condense outside the frost line
Beyond the frost line it was cold enough for hydrogen compounds to condense into ices, the solid seeds were built of ice along with metal and rock.
Why are jovian planets bigger than terrestrial planets?
Because hydrogen compounds were nearly three times as abundant in the nebula as metal and rock combined, the total amount of solid material was far greater beyond the frost line than within it.
The process by which small "seeds" grew into planets
"pieces of planets"
A stream of charged particles (such as protons and electrons) continually blown outward in all directions from the Sun
The period in the first few hundred million years after the solar system formed during which the tail end of planetary accretion created most of the craters found on ancient planetary surfaces
A collision between a forming planet and a very large planetesimal, such as is thought to have formed our Moon.
athe process of determining the age of a rock (i.e., the time since it solidified) by comparing the present amount of a radioactive substance to the amount of it's decay product.
The spontaneous change of an atom into a different element, in which its nucleus breaks apart or a proton turns into an electron. It releases heat in a planet's interior.
has a nucleus that can undergo spontaneous change.
The time it would take for half of the parent nuclei in the collection to decay.
The extension of the study of Earth's surface and interior to apply to other solid bodies in the solar system, such as terrestrial planets and jovian planet moons.
vibrations that travel both through the interior and along the surface after an earthquake.
The highest density material, consisting primarily of metals such as nickel and iron, resides here.
Rocky material of moderate density-mostly minerals that contain silicon, oxygen, and other elements.
The lowest-density rock, such as granite and basalt (a common form of volcanic rock)
gravity pulls the denser water to the bottom, driving the less dense oil to the top in what process?
a planet's outer layer consists of relatively cool and rigid rock
The surface of the terrestrial worlds can change with time. what is the process that describes these ongoing changes?
What three ways do the interior of planets get hot?
heat of accretion, heat from differentiation, Heat from radioactive decay.
Heat of accretion
Accretion deposits energy brought in from afar by colliding planetesimals. As a planetesimal approaches a forming planet, its gravitational potential energy is converted to kinetic energy, causing it to accelerate. Upon impact, much of the kinetic energy is converted to heat, adding to the thermal energy of the planet.
Heat from differentiation
The sinking of dense material and rising of less-dense material means that mass moves inward, losing gravitational potential energy. This energy is converted to thermal energy by the friction generated as materials separate by density
Heat from radioactive decay
The rock and metal that built the terrestrial worlds contained radioactive isotopes of elements such as uranium, potassium, and thorium. When radioactive nuclei decay, subatomic particles fly off at high speeds, colliding with neighboring atoms and heating them. In essence, this transfers some of the mass-energy of the radioactive nuclei to the thermal energy of the planetary interior.
Three basic cooling processes
Convection, conduction, and radiation
Process by which hot material expands and rises while cooler material contracts and falls. It therefore transfers heat upward, and can occur whenever there is strong heating from below.
Transfer of heat from hot material to cooler material through contact. Occurs through the microscopic collisions of individual atoms or molecules. Molecules of materials in close contact are constantly colliding with one another, so the faster-moving molecules in hot material tend to transfer some of their energy to the slower-moving molecules of cooler material.
Planets ultimately lose heat to space through radiation. Objects emit thermal radiation charateristics of their temperatures; this radiation (light) carries energy away and therefore cools an object. Because of their relatively low temperatures, planets radiate primarily in the infrared.
an individual small region of convecting material.
The three basic requirements for a global magnetic field
- an interior region of electrically conducting fluid (liquid or gas), such as molten metal
- Convection in that layer of fluid
- At least moderately rapid rotation
What processes shape planetary surfaces
- impact cratering
what are the three types of volcanic features
- volcanic plains- the runniest lavas flow far and flatten out before solidifying
- Shield volcanoes-somewhat thicker lavas tend to solidify before they completely spread out
- stratovolcanoes- the thickest lavas cannot flow very far before solidifying and therefore build up tall steep volcanoes
a mixture of many different minerals that erupts from volcanoes as a high-density but fairly runny lava
What are the key effects of atmospheres
- 1. They create pressure that determines whether liquid water can exist on the surface
- 2. Absorb and scatter light. Scattering makes daytime skies bright on worlds with atmospheres, and absorption can prevent dangerous radiation from reaching the ground.
- 3. Create wind and weather and play a major role in long-term climate change.
- 4. Interactions between atmospheric gases and the solar wind can create a protective magnetosphere around planets with strong magnetic fields.
- 5. Can make planetary surfaces warmer than they would be otherwise via the greenhouse effect
- Gases that are particularly good at absorbing infrared light. Examples: water vapor, carbon dioxide, and methane.
- These gases absorb infrared light effectively because their molecular structures begin rotating or vibrating when struck by an infrared photon.
The process by which greenhouse gases in an atmosphere make a planet's surface temperature warmer than it would be in the absence of an atmosphere.
Without the greenhouse effect what two things effect the surface temperature
- The planet's distance from the sun, which determines the amount of energy received from sunlight. The closer a planet is to the Sun, the greater the intensity of the incoming sunlight.
- The planet's overall reflectivity, which determines the relative proportions of incoming sunlight that the planet reflects and absorbs. The higher the reflectivity, the less light absorbed and the cooler the planet.
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