Since Venus is in an orbit interior to Earth’s orbit, it shows phases.
a) (2 pts) When Venus is in its full phase as viewed from the Earth, is the angular size of the entire planet larger or smaller than its angular size in its crescent phase?
b) (4 pts) Use a diagram to help explain your answer to (a). A diagram by itself is not a sufficient answer.
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The absence of liquid water on Venus is a crucial component to the process that warmed the planet up to its current extremely hot temperature. What role does liquid water play in the Carbon cycle on Earth and how does its absence lead to global warming?
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Craters on Venus are more numerous than on Earth, telling us that the surface is about 500 million years old, but it isn’t as old as, say, the lunar surface, so we know that some process is getting rid of craters on Venus.
a) (4 pts) Do craters disappear gradually on Venus over time, like on Earth?
b) (8 pts) What evidence confirms your answer to part (a)? Explain.
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Like Earth, Venus’ size apparently allows it to retain sufficient internal heat to support ongoing geological activity.
a) (6 pts) How do the mountains on Venus provide evidence of plate tectonics?
b) (6 pts) Even though we cannot see the surface, we know there is ongoing volcanism on Venus. How do we know? Explain.
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Though Venus’ atmosphere it today about 100 times thicker than Earth’s, the Argon abundance on Venus is about the same as Earth.
a) (4 pts) Before the runaway greenhouse effect took hold, what was Venus’ primitive atmosphere like, compared to the Earth (thicker, thinner, same, can’t determine)?
b) (8 pts) Explain your answer to part (a).
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Assuming that the runaway greenhouse theory is correct for Venus, water eventually rose to the upper atmosphere where it was broken apart. If this happened, then we should expect the ratio of heavy water to light water on Venus to be different from that of the Earth. Assuming this ratio is 1/10,000 (0.01%) on Earth...
a) (4 pts) Do we expect the ratio on Venus to be (larger, smaller, same, can’t determine)?
b) (8 pts) Explain your answer to part (a).
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What two properties of Argon enable the abundance of this gas in Venus’ atmosphere to remain constant over time in spite of the runaway greenhouse effect? Explain each property.
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Radio observations carried out by the Magellan spacecraft orbiting Venus enabled us to see the surface of Venus, which is much more heavily cratered than the Earth’s surface.
a) (4 pts) Is the surface of Venus (younger than, older than, same age as, can’t determine) the surface of the Earth?
b) (8 pts) Explain your answer to part (a).
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The distance from Earth to Venus varies by about a factor of six over the course of a year. Likewise, the distance from Earth to Mars varies by about a factor of six over the course of a year. Despite this, Venus is always roughly the same brightness in the sky while Mars varies in apparent brightness considerably. Explain this difference.
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Though Venus is a planet shrouded in mystery, we can speculate about its past and present from a few clues.
a) (5 pts) What evidence do we have that Venus underwent a cataclysmic episode of volcanism (or some other global geological event) about 500 million years ago? Explain.
b) (3 pts) What evidence do we have that volcanism on Venus on ongoing during the present time? Explain.
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The characteristics of the craters on the surfaces of the Earth and Venus are indicators of the very different geological histories of these two worlds.
a) (6 pts) How do we know that craters on the surface of the Earth are mainly erased through gradual processes?
b) (6 pts) How do we know that craters on the surface of Venus were mainly erased by some kind of catastrophic event?
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Explain why normal water (atomic mass = 18) is more likely to escape from Venus than “heavy water” (atomic mass = 20).
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One of the interesting things about the planet Venus is that it rotates in a retrograde direction (clockwise as seen from above). In other words, it rotates in a direction opposite to its orbital direction (counter-clockwise as seen from above), as shown in the diagram below. Assume for simplicity that Venus has a rotation period of 24 hours.
The sidereal day on Venus measures how long it takes for a distant star to return to the same location on the sky. The solar day measures how long it takes for the Sun to return to the same location on the sky.
a) (2 pts) Which is longer on Venus? (sidereal day, solar day, same length).
b) (6 pts) Explain your answer to part (a).
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Astronomers think that Venus lost its water via a process known as the runaway greenhouse effect.
a) (7 pts) Describe how the Carbon cycle on Venus was crippled over time, and explain how this effect led to the loss of water vapor and the addition of Carbon Dioxide into the atmosphere, thus worsening the effect.
b) (7 pts) An alternate theory that attempts to explain why Venus has little water today is this: Venus simply never accumulated any water in the first place, unlike Earth. What evidence in Venus' atmosphere today contradicts this? Explain.
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We know that Venus' proximity to the Sun led to both higher surface temperatures (which leads to more vaporization of water into the atmosphere) and more exposure to ultraviolet light (which breaks up water in the atmosphere, depleting it). This small difference between Venus and Earth led to the runaway greenhouse effect.
a) (7 pts) Explain the evidence that leads Astronomers to believe that Venus and Earth once had very similar atmospheres.
b) (7 pts) Explain how the positive feedback cycle of the runaway greenhouse effect leads to both higher temperatures and further loss of water from Venus' atmosphere.
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Today, Venus has much less water than Earth, even though we believe that both atmospheres started off with very similar abundances of water (and everything else, for that matter). Astronomers believe that this lack of water on Venus today is due to the runaway greenhouse effect.
a) (7 pts) Explain why we believe Venus and Earth once had similar amounts of water in their atmospheres.
b) (7 pts) The ratio of heavy water to normal water in Venus' atmosphere is seen as evidence that the runaway greenhouse was indeed the mechanism that depleted the water on Venus (rather than any other proposed mechanism). How does this ratio differ from that on Earth, and why does this evidence support the runaway greenhouse theory (you only need to discuss the runaway greenhouse, not the other mechanisms)?
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We believe that the runaway greenhouse effect led to the loss of virtually all the water on Venus. An alternate possibility is that the water has somehow been lost to underground reservoirs, locked deep inside the planet. Explain how the abundance of heavy water (relative to normal water) in Venus’ atmosphere supports the runaway greenhouse interpretation rather than the “lost underground” interpretation.
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This question deals with the geological history of Venus.
a) (6 pts) Besides the fact that they are more numerous on Venus, what is the difference between craters on Venus and craters on the Earth? Explain why that difference leads us to believe that a catastrophic event wiped out craters on Venus long ago.
b) (8 pts) Describe how Astronomers think craters were wiped out on Venus. An alternate theory is that volcanic eruptions erased the craters. State briefly the evidence or argument against this volcanic theory.
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Astronomers believe that the reason lacks a significant amount of water today is because of the process known as the Runaway Greenhouse Effect (RGE).
a) (6 pts) Name and explain two reasons that Venus is more suspectible to the RGE while Earth is not.
b) (8 pts) There is very little water in Venus' atmosphere. Of the water present, the ratio of light to heavy water is different on Venus than on Earth. How does the RGE account of the fact that lighter water is depleted on Venus relative to heavy water?
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While we have seen evidence of geological activity that tells us Venus has a significant internal heat source, recent measurements show that Venus has no detectable magnetic field. Name and briefly explain the two pieces of evidence that show us Venus has ongoing geological activity (volcanism), then explain why Venus has no magnetic field.
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Presumably, early in its history, Venus had an abundance of water on its surface.
a) (4 pts) Explain why we think this is true.
b) (4 pts) Would Venus have had high and low tides if it had liquid water on its surface? Justify your answer.
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Describe in detail the positive feedback mechanism called the "runaway greenhouse effect" (RGE) that appears to have resulted in the current conditions on Venus today. As part of your answer, briefly explain two reasons why Venus has undergone this process while the Earth has not.