OOOO - Mars
We think that the Martian atmosphere was lost due to a process called impact erosion. Name and explain two reasons why the Earth did not suffer a similar fate.
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Mars Pathfinder has measured large daily variations in the wind speed and direction on the surface of Mars, but it doesn’t seem related to the global seasonal changes we’re familiar with. What causes these variations and why don’t we have similar large variations on small scales here on Earth?
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Even though we can’t see beneath the Martian surface, we have indirect evidence that there is a layer of frozen ice there, thanks to observations of certain craters on Mars.
a) (6 pts) Explain this evidence.
b) (6 pts) Even if Mars were as warm as the Earth, liquid water could no longer exist on the surface of Mars. Explain why.
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When the Pioneer spacecraft first arrived to survey Mars, the planet looked like a blank slate. Apparently, this is because Mars periodically suffers from planet-wide dust storms the likes of which we never see on Earth. Why do such storms occur on Mars but not Earth? Explain.
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Theorists tell us that the Sun was once substantially fainter than it is today, yet we know Mars was much warmer than its current -50° C a long time ago by at least 50 degrees. Name one piece of evidence in support of this fact about Mars and explain it.
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Argon reconstruction of the Martian atmosphere shows that the primitive atmosphere of Mars apparently had no Argon-36.
a) (8 pts) Why do we think this conclusion is incorrect? Explain.
b) (4 pts) Although Argon-36 is gone from Mars, there is apparently still some Argon-40 remaining. Where does it come from?
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Like Argon (atomic mass = 40), Carbon Dioxide (atomic mass = 44) is a very heavy gas found on Mars that is unlikely to escape over time.
a) (6 pts) Other than its high mass, why is Argon such a good tracer of Mars’ original atmosphere and not Carbon Dioxide? Explain.
b) (6 pts) The Argon abundance on Mars is only about 1% of Earth’s Argon abundance. Assuming Argon hasn’t left Mars’ atmosphere somehow since Mars formed, what does this imply about how Mars’ original atmosphere compared to that of Earth? Explain.
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One proposed mechanism that might have depleted the Argon (and virtually everything else) in the Martian atmosphere is a giant impact that occured sometime after the planet formed. What direct evidence contradicts this idea (I’m not asking for philosophical objects like “not falsifiable” here...in this case, the giant impact theory is falsifiable and I’m asking you to tell me how it is falsified)?
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Explain two pieces of evidence that lead us to believe that Mars has large amounts of frozen water located just beneath its surface.
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One reason Argon is such a good tracer of the original Earth atmosphere is that it is a noble gas, meaning that it doesn’t interact with other atoms in Earth’s atmosphere.
a) (6 pts) Name and explain another reason why Argon makes a good tracer of Earth’s original atmosphere.
b) (6 pts) Explain the evidence leads us to believe that most of the original Argon has somehow escaped from Mars sometime in the past.
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Explain why the low density of impact craters on the slopes of Mars’ largest volcano, Olympus Mons, leads theorists to believe that Mars should have a detectable magnetic field.
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The process of Argon reconstruction is apparently not valid for the Martian atmosphere because Argon reconstruction implies that Mars’ original atmosphere was only about 1% as thick as the Earth’s.
a) (6 pts) Explain what process depleted the Argon in the Martian atmosphere and what evidence led us to believe that it wasn’t some other process that depleted the Argon.
b) (6 pts) What evidence on the Martian surface implies that the Martian atmosphere was once very similar to Earth’s atmosphere? Explain.
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Some scientists believe that Mars once had primitive life forms, but there is no longer any evidence of life (at least, not above ground). One factor that may lead scientists to be skeptical about life on Mars is the apparent lack of a significant magnetic field on Mars.
a) (4 pts) Explain why the presence of a magnetic field is thought to be necessary for the existence of life as we know it.
b) (4 pts) Besides the fact that Mars rotates at about the same rate as Earth, what direct observational evidence on the surface of Mars leads us to believe that it should have a magnetic field? Explain.
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The Martian volcano Olympus Mons is the largest volcano in the solar system, covering a land area about equal to the state of Texas (and it’s just one mountain!).
a) (4 pts) Explain how the lack of plate tectonics on Mars contributed to the large size of this volcano.
b) (4 pts) Even if Mars did have plate tectonics, we would expect the mountains on Mars to be generally larger than the mountains on Earth. Explain why.
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According to the “impact erosion” theory for the loss of Mars’ atmosphere, Mars suffered far more impacts (due to its proximity to the asteroid belt) during the last few billion years than Earth or Earth’s Moon. Assuming the impact erosion theory is correct, suppose we are looking at a section of Mars and of Earth’s Moon, each with roughly the same crater density.
a) (2 pts) The Martian terrain will have a radioactive dating age (younger, older, the same) as the Moon’s terrain.
b) (6 pts) Explain your answer to part (a).
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Recently, scientists detected possible signs of ancient life inside a meteorite that had Mars as its parent body.
a) (7 pts) One tell-tale sign that indicated the rock came from Mars was the numerous tiny pockets of gas inside. Explain how these were used to determine the origin of the meteorite.
b) (7 pts) Normally, scientists can use reflection spectra to determine the parent body of a meteorite, but not in this case. This meteorite is a dull grey color while the Martian surface is very red. Explain the difference in colo--
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Astronomers believe that the Martian atmosphere was once very similar to Earth's atmosphere, and there have been several possible theories proposed to explain why these two atmospheres evolved to a point where they are so different today.
a) (6 pts) Name and explain the evidence that suggests Mars and Earth once had similar atmospheres.
b) (8 pts) Explain how the "freeze out" theory proposes Mars lost its atmosphere. You do not need to go into evidence for/against this theory, just describe it.
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Recently, scientists have carefully studied a meteorite found in Antarctica and discovered that not only does it have Mars as its parent body, but it may also show fossilized signs of primitive life in its interior, life that may have originated on Mars.
a) (4 pts) Aside from the reflection spectrum, tiny gas bubbles inside the meteorite provide evidence that the meteorite is originally from Mars. State why in a brief sentence.
b) (4 pts) Although the Martian surface is mostly red due to oxidation (rusting), the Martian meteorite has a much darker color. Briefly explain why this difference exists (in a single sentence).
c) (6 pts) This meteorite probably left Mars via an impact, which knocked fragments of the surface off, some of which eventually fell to Earth millions of years later. Name and explain (one sentence each) two reasons why Mars is more susceptible to losing material via impacts compared to the Earth.
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Astronomers have concluded that Mars once had an Earthlike climate, but today it is a harsh, cold environment with a very thin atmosphere.
a) (6 pts) Explain briefly the evidence that makes us think Mars' atmosphere was once similar to the Earth.
b) (8 pts) How and why does the abundance of Argon on Mars imply that the atmosphere was originally very thin?
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Two types of impact theories attempt to explain what has happened to the water that once flowed in abundance on the surface of Mars.
a) (10 pts) Why do we believe an impact or series of impacts is responsible for the loss of the Martian atmosphere? Why is the "impact erosion" theory believed over the "giant impact" theory?
b) (4 pts) The Mars Odyssey probe is about to start searching for signs of water beneath the surface layers of Mars. Exactly how will the spacecraft be able to tell where the water can be found?
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One theory that explains why the Martian atmosphere today is very thin is the "freeze out" model, which says Mars' atmospheric gases are now locked up in the crust somehow, frozen in place.
a) (10 pts) Explain what triggered the beginning of this process and how this process presumably got rid of the Martian atmosphere.
b) (4 pts) Briefly explain the evidence in opposition to the freeze out theory.
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Astronomers have studied the atmosphere of Mars using the concept of spectral fingerprints and determined that the composition is very thin and largely composed of Carbon Dioxide.
a) (7 pts) Explain how Astronomers are able to determine the composition of the Martian atmosphere. As part of your answer, be sure to explain how Astronomers can distinguish absorption lines of the Martian atmosphere from other absorption lines in the spectrum (that may originate in the Sun's outer layers or the Earth's own atmosphere).
b) (7 pts) It is no surprise that the only gas in the Martian atmosphere is a rather heavy gas like Carbon Dioxide (total atomic mass = 44) as opposed to something lighter like water vapor (total atomic mass = 18). Explain why less massive gases are more likely to stick around in a planetary atmosphere (remember, an equation or a description of an equation is not a sufficient answer...you must explain why there is a relationship between gas mass and the ability of gas to escape a planet).
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Recently, a meteorite found in Antarctica was determined to have originated from Mars. In addition, some scientists claim that evidence from microbial life forms on Mars was found inside the rock.
a) (4 pts) This meteorite was not red like much of the Martian soil. Why not?
b) (4 pts) What conclusive evidence told scientists that the meteorite indeed originated from the planet Mars?
c) (6 pts) Why is it scientifically important to determine whether or not life once existed on Mars? If we do find that life existed on Mars, what does that imply about life on Earth? What if life didn't exist on Mars? What does that imply? Briefly explain your answer.
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Name and explain the reason many scientists feel that Mars is small relative to the other terrestrial planets Earth and Venus.
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How do we know the Martian atmosphere was once Earth-like? Answer in a brief sentence, then briefly explain the "freeze out" theory for the Martian atmosphere, and explain a major line of evidence that refutes this theory.
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Two different theories that try to explain the loss of the Martian atmosphere over time are "impact erosion" and "sputtering".
a) (7 pts) Explain how "impact erosion" works, then name (no explanation needed) two reasons why a similar process probably cannot happen on the Earth.
b) (7 pts) Explain how "sputtering" works, then briefly explain one reason why a similar process cannot happen on Earth.
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You have been given the average density of rock, metal, ice and gas on the cover page. Assume the density of Mars is 2 grams/cc. A newly discovered planet X orbits another star like our own Sun. We find that X has a mass one-fourth that of Mars. We also find that the radius (size) of planet X is one-half the radius of Mars.
a) (8 pts) What is the density of planet X in grams/cc? Show your work.
b) (6 pts) Describe the composition of Mars in terms of how much metal, rock and/or ice there might be, based on your knowledge of the density.
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Explain why the Earth's sky is blue while the Martian sky is pink (what causes each color).
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There are two possibilities for the original atmosphere of Mars: one is that it was thick, warm and Earthlike. The other is that it was very thin like it is today. Name and explain the evidence that supports each possibility.
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One reason some Astronomers believe the "freeze out" theory is that we know geological activity ceased on Mars sometime within the last 1-2 billion years.
a) (7 pts) Why has volcanism ceased on Mars but not on the Earth? Explain.
b) (7 pts) How do we know how long ago volcanism came to an end on Mars? Explain.