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Astronomy test 3
Terms in this set (40)
From your textbook's chapter 7.1, explain what a "TNO" is. Where do we typically find TNO's in our solar system? About how many TNO's have been discovered?
TNO: trans-neptunian objects (smaller worlds beyond Neptune.) More than 2600 have been discovered
From your textbook's chapter 7.2, explain how the internal structure of the terrestrial planets tells us that these planets must have once been very hot and mostly liquid, even though they are mostly solid today.
The densest metals are in the central core, with the lighter silicates near the surface, which is the result of differentiation
From your textbook's chapter 7.2, explain how and why the history of geologic and volcanic activity on a world is related to its size.
It is like a baked potato: the larger it is, the longer it takes to cool off. Therefore, the moon is already cooled off but the Earth still has molten interiors today because it is so large
From your textbook's chapter 7.3, (a) describe how we estimate how old a planetary surface is (how long since it has undergone a major change). Also, (b) describe how we determine the age of a rock (how long ago it solidified).
A) We count the number of impact craters. Craters have been pretty constant for several billion years, so the number of craters is proportional to when the surface solidified.
B) We measure the age of rocks by radioactivity. For example, almost exactly half of the nuclei will have decayed by its half-life.
From your textbook's chapter 7.4, we find many "exceptions to the rule" in our solar system, such as the backwards rotation of Venus or the crazy tilt of the rotation axis of Uranus. Name and briefly explain the part of our theory of planetary formation can help explain these exceptions.
Planetesimals: precursors of the planets. They were believe to be the "exception of the rules" because they cause enormous collisions which can knock things out of balance.
From your textbook's chapter 21.3, explain why it is easier to search for planetary systems when the protoplanetary disk contains a lot of dust and gas before it gathers into planets instead of when planets have formed from all of the dust and gas in the disk.
It is easier to search for planetary systems before they form because we are able to detect radiation from all the dust particles. We can also detect the silhouette of the disk if it is blocking the light source behind it. Once the planet has formed, the dust is hidden in the interior of the plant. Thus making it too hard to detect the radiation.
From your textbook's chapter 21.4, explain how we deduce the approximate size (or radius) of transiting exoplanets. Also, how do we deduce the density of these exoplanets in order to determine whether they are rocky or gaseous?
1)we can determine the mass from the transit. The shadow of light can show. us how big an exoplanet is. 2) we can see how much the star moves -mass/ volume
From your textbook's chapter 21.4, explain why it is easier to use the infrared part of the spectrum (instead of the visible part) in order to directly image planets orbiting around other stars.
We have to use the infrared spectrum because when we look at a planet, even with the best telescopes, the radiation from its parent star is too bright to get a clear view
From the Scientific American article "What Is a Planet?" - What are the three properties an object in our solar system must have in order to be officially designated as a planet by the astronomical community?
size, shape, composition
From the Scientific American article "What Is a Planet?" - What were the original seven planets, and why wasn't Earth on the list?
Sun, moon, mercury, Venus, mars, Jupiter, Saturn. Earth was not on the list because it was considered the center of our universe, not a planet
From the Scientific American article "What Is a Planet?" - In the year 1851, the number of planets had grown to 15. What were all of these extra planets and why were they eventually disqualified from planet status?
The extra planets were identified as asteroids. They decided to list them in order of discovery rather than by distance from the sun.
From the Scientific American article "What Is a Planet?" - What is Eris? Why did the discovery of Eris lead the IAU to reevaluate the rules by which we call objects planets?
Eris is a KBO bigger than Pluto. If Pluto was considered a planet then Eris would be too. Along with so many more KBO's that are larger than Pluto so IAU had to reevaluate the rules of a planet
From the Scientific American article "Secrets of Primitive Meteorites" - Describe the general structure and appearance of chondrites. What makes them important to astronomers studying the early solar system and planetary formation?
Chondrites are the oldest rocks scientist have ever touched. They are made up of silicate rich dust drops, dust, metals and other materials that have solidified and now are chipped/rocky. If scientists fill in the gaps of the chondrites then they can better understand the process of formation of asteroids and planets
From the Scientific American article "Secrets of Primitive Meteorites" - The author asserts that carbonaceous chondrites probably orbit furthest from the Sun compared to any other type of chondrite. Explain why the author thinks this is true.
They have the most dust concentration and the presence of organics which is an indicator of being furthest from the sun
From the "Origin of the Solar System" video, briefly describe two things are mentioned in the video that allow microscopic dust particles to start quickly growing into much larger objects?
When they are very little they gently bump into each other and start forming together to slowly grow. Then, when they are large enough to become planetesimals, they exert a gravitational pull and collide to form port-planets
From the "Origin of the Solar System" video, briefly describe three reasons why terrestrial planets tend to lose their primary atmospheres shortly after formation unlike the gas giants, which still have the primary atmospheres they formed with.
1) Temperatures are warming near port-star -> hot gasses move faster than cold gasses
2) Low mass planets have less gravity/ low escape velocity -> hot gasses escape
3) Protostar's stellar wind is stronger in the inner solar system -> which makes it even harder for them to stick around
From the "Crash Course: Exoplanets" video: Around what kind of star were the first two planets discovered? Why was this discovery not very "satisfying" to Astronomers who were hoping to gain more insight into our own solar system?
The Pulsar. It was not satisfying because it looked like the exoplanets had formed from material left over after the supernova explosion.
From the "Crash Course: Exoplanets" video: The first planet discovered around an "ordinary" star was 51 Peg b. The fact that it is very massive (more massive than Jupiter) and also orbits very close to its parent star (8 million km compared to the 55 million km radius of Mercury's orbit, with an orbital period just over 4 days) was surprising, because our model of planetary formation predicted that no giant planets could form that close to their parent star. So how do we think 51 Peg b got there, exactly?
It was probably formed further out then it migrated inward, just like Jupiter, as it interacted with the disk of planet forming material around the star
From the "Crash Course: Exoplanets" video: What was so significant about the discovery of the exoplanet HD 209458b, discovered in 1999? Explain.
It created a transit (when it passes in front of its' star it blocks the light). Therefore, it was the first independent confirmation of an exoplanet
From the video "Life Beyond Earth, Part 1," we search the cosmos for the three things terrestrial life required. What are these three things, and for each ingredient, what is an example of a place where it may be found outside of our solar system?
Energy- the stars
Water- comets, the organ nebula
Organic Molecules that contain carbon- the organ nebula
From the video "Life Beyond Earth, Part 1," on the five km highway of life, the first life forms are found about 3.75 km away from where we are today (3.75 billion years ago). What were the first life forms that were common on Earth for 3 billion years after this time, and what were they like? Briefly describe them.
The first life forms on Earth were blobs of single-celled bacteria and algae called Stromatolites, which look like rocks
From the video "Life Beyond Earth, Part 1," critics of Darwinian evolution say it is impossible to produce complex life forms just from random mutations (just like it is impossible to randomly organize letters of the alphabet to produce "King Lear"). How do biologists respond to this argument?
They say that evolution is not just a random chance, it is a matter of discarding the variations that do not work and keeping the ones that do
From the video "Life Beyond Earth, Part 1," explain what is the habitable zone in our solar system. Also, explain two reasons why, about the time we were starting to venture into space, astronomers felt that life may exist on Mars or Venus.
The habitat zone is close enough to the sun for solar energy to drive the chemistry of life but not too close to boil. Astronomers thought life may exist on mars/venus because: 1) they believed Venus has a case of greenhouse effect, 2) they might have hot molten cores that could power volcanoes like earth
From the video "Life Beyond Earth, Part 1," describe what the Magellan spacecraft discovered about the past history of the planet Venus, starting about 500 million years ago?
Venus turned itself inside out with dramatic volcanic floods that covered up most of the surface which caused greenhouse effect and climate change
From the video "Life Beyond Earth, Part 1," what evidence discovered by the Viking orbiters on Mars indicated the Mars must have once had a thicker, warmer atmosphere than it does today?
The viking orbiters found dried up river beds which indicates a denser atmosphere and water was there
From the video "Life Beyond Earth, Part 1," Freeman Dyson explains that there are two possibilities regarding the origin of life. Either it came into being gradually through chemistry and steps we could hope to retrace (and could presumably be reproduced elsewhere) or life is some kind of extraordinary fluke. If the answer to the question of the origin of life is the first possibility, what does that imply about life beyond Earth? What if the answer is the latter possibility?
If it was gradually through chemistry then it presumably happens all over the cosmos and we should find a lot of life; if it is a fluke then we will not find life
From the video "Life Beyond Earth, Part 1," explain what is meant by the term "gravitational habitable zone" and what discoveries on Earth have led us to make plans to search non-traditional places like Europa for life.
Gravitational Habitable Zone is the energy from the gravitational pull combined with the force of the moons pulling on each other as they orbit which causes them to flex tidally. This creates heat in their interiors and gives them molten cores and active surfaces. The discovery that life can grow in extreme conditions on Earth led to a search
From lecture, during the collapse of our spherical presolar nebula, the shape of the nebula changed from a roughly spherical shape into a flattened disk instead of into a smaller spherical shape. Explain what caused this change of shape.
The change of shape of our Nebula is because as it shrinks, the gravity compacts but centrifugal force opposes gravity from the sides. Therefore it gets smushed down into a disk.
From lecture after the protoplanetary disk had time to cool, some substances began to condense from the cloud of gas/dust into solid form. Explain why rock and metal condensed in the region closer to the protosun while rock, metal and ice condensed in the region further from the protosun.
From lecture explain two reasons why massive outer planets like Jupiter and Saturn can capture and hold Hydrogen and Helium gas while the terrestrial planets closer to the Sun (like Earth) cannot.
1) it is a really high escape velocity
2) because Jupiter is further away, the gas is much cooler, therefore slower and less chance of escape.
From lecture, what are two examples of sources and two examples of sinks for planetary atmospheres?
Sources: 1) impacts rich with volatiles
2) outgasses, gas released by melted rocks
Sinks: 1) condensation
2) chemical reaction
3) thermal escape
From lecture, explain what is escape velocity, and explain why it is easier for gases to escape the atmosphere of a hotter planet as opposed to a colder planet.
Escape velocity is the speed needed to escape a planet's gravity. It is easier to escape the atmosphere of a hot planet because when it is cold, it is much slower.
From lecture, explain why Earth can hold on to gases like Carbon Dioxide but not Hydrogen.
Earth cannot hold onto hydrogen because heavier particles move slower so the larger/ heavier gasses are less likely to reach escape velocity.
From lecture, explain what are the three rules of Doppler shifting.
1) objects moving toward an observer have their waves shorter ( blueshifting)
2) objects moving away from an observer have their waves longer ( redshifting)
3) the amount of shift depends on radial velocity (line-of-sight)
From lecture, explain the difference between radial velocity and transverse velocity. If you have two stars with the same velocity but star A is moving directly away while star B is moving transverse to your line of sight, which will show a larger Doppler shift and why?
If a star is moving along your line-of-sight then it is radial. If it is moving across then it is transverse. Radial velocity shows a larger Doppler shift because transverse velocity cannot be detected.
From lecture, in the Doppler wobble method of exoplanet detection, explain what we observe and how that turns into a graph of radial velocity vs time.
We do not see the color of the stars, we only see the shifting. It takes a long time for a shift to occur for us to detect it. We measure the spectrum lines through and calculate the doppler shift from that then graph it
From lecture, once we have a graph of a star's radial velocity vs time, what two things on that graph do we measure? For each of these two things, explain what property of the companion planet do deduce (explain why it there is a relation between what we measure and the property of the planet).
1) the time it takes to complete a wobble- period of a wobble is equal to star to planet distance 2)amplitude: max radial velocity- companion planet mass
From lecture, if the planetary system is face-on with respect to our line of sight instead of edge-on, we will not be able to detect any exoplanets with the Doppler wobble technique, even if the star is wobbling. Explain why not.
We could measure or graph it but it would be a straight line because there would be no velocity so we really cannot measure that. The reason: the stars are wobbling face-on exhibit no radial velocity. So it will look like the star is not moving at all
From lecture, if the planet system is tilted with respect to our line of sight, our estimate of the companion planet's mass will be too small. Explain why.
From lecture, explain why Astronomers feel that, if other intelligent beings exist in the galaxy, our first evidence of them is more likely to be a signal sent to us from a distant world rather than an actual spaceship showing up to fly around in our planet's atmosphere.
Communication is much easier to use then visiting another planet. Building a spaceship would cost too much money. We could just send a signal.
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