Initial experiments by the Viking lander showed positive results when testing for life. Describe how the use of a control experiment showed these initial results were false.
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To date, over a dozen extrasolar planets have been discovered via indirect techniques, mainly using Doppler shift information.
a) (6 pts) Why have only large planets (with masses about equal to the mass of Jupiter or larger) been discovered so far? Explain.
b) (6 pts) Why have only planets with very short periods (typically a year or less) been discovered so far? Explain.
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To date, almost a dozen extrasolar planets have been discovered. These planets all seem to be very massive (hundreds of times the mass of Earth) and extremely close to their parent stars (with orbital periods of a year or less); however, we have reason to believe that this sample of planets is probably not representative of all the planets that may exist in our galaxy. Explain two reasons why this sample is probably not a representative sample, using physical arguments (in other words, don’t use statistical arguments like “the sample size is too small”) that we’ve discussed in class.
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About 10-15 years ago, scientists set out to use the latest infrared technology to search for disks of gas and dust around nearby Sun-like stars. They expected to find such disks around many such stars. Explain why they expected this, in 2-3 sentences (note that I am not asking how they did it).
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On the graph below, sketch a graph of continuous radiation for a Sun-like star. On the same graph, sketch a graph of continuous radiation for a planet like Jupiter. Use this graph to help explain why we can only hope to directly detect planets around other stars by using infrared cameras rather than cameras that use visible light.
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A method of finding large planets around other stars involves detecting the stars’ “wobble” in response to the gravitational pull of the companion planet.
a) (4 pts) For systems in which the planetary orbit is viewed “face on”, we are unable to use Doppler shift measurements to detect the star’s “wobble”. Explain why.
b) (8 pts) Describe the technique we use to detect planets in “face on” systems.
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In the last 15 years, Doppler shift measurements of stellar “wobble” have revealed several Jupiter-sized planets around other stars with periods of less than one year. In our own solar system, the planet Jupiter has a period of about 12 years. We haven’t yet found any Jupiter-sized planets around other stars with such long periods as 12 years or more. Explain why we have not seen such long-period planets in 2-3 sentences.
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Explain why the number of currently existing, intelligent and communicative civilizations in our galaxy is proportional to the average lifetime of such civilizations (I’m not asking you to restate the Drake equation...I’m asking you to explain it).
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Assuming that if any aliens are trying to contact us, they are using very narrow-bandwidth signals, explain why we would want to search the spectrum using very narrow bandwidth channels (even though such a search would be much more time consuming than splitting the spectrum up into fewer broad channels).
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When we search for signals from other intelligent civilizations, one of the regions of the spectrum that we avoid is the ultraviolet (UV) portion of the spectrum. Give two reasons why it would probably be a waste of time to search this region of the spectrum.
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Astronomers have recently deduced the existence of planets orbiting other Sun-like stars in our galaxy by observing the periodic Doppler shifts of these stars, which indicate changing radial velocity in response to an orbiting planet.
a) (7 pts) Star X wobbles in one complete cycle every seven months. Star Y wobbles in one complete cycle every two months. Assuming both stars are exactly like the Sun (same mass), which star's planet is at a larger distance from its parent star? Give one reason to help explain your answer.
b) (7 pts) Star A and B wobble with exactly the same period. Star A's radial velocity with respect to the Earth varies from 15 meters/sec toward us to 15 meters/sec away from us. Star B's radial velocity varies from 7 meters/sec toward us to 7 meters/sec away from us. Which star probably has a more massive planet as a companion? Justify your answer.
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Astronomers have recently deduced the existence of planets orbiting other Sun-like stars in our galaxy by observing the periodic Doppler shifts of these stars, which indicate changing radial velocity in response to an orbiting planet.
a) (7 pts) Star A and B wobble with exactly the same period. Star A's radial velocity with respect to the Earth varies from 5 meters/sec toward us to 5 meters/sec away from us. Star B's radial velocity varies from 12 meters/sec toward us to 12 meters/sec away from us. Which star probably has a more massive planet as a companion? Justify your answer.
b) (7 pts) Suppose star A is actually not wobbling edge-on with respect to Earth but rather halfway between edge-on (where the radial velocity equals the orbital velocity at times) and face-on (where the radial velocity of the wobble is always zero, undetectable). Is the true mass of star A's companion larger or smaller than the mass we would estimate by assuming star A's wobble is seen edge on? Justify your answer.
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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 colors.
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Many scientists tend to believe that there is life elsewhere in the Universe, although there is some doubt as to whether we will know the answer to this question definitively in our lifetimes.
a) (7 pts) Explain what the Copernican Principle is and why the fact that most scientists assume this is true leads them to believe there is life elsewhere in the Universe.
b) (7 pts) Suppose communication with the Mars Polar Lander is somehow restored and the lander indicates that there is indeed evidence for primitive life on the surface of Mars. How and why would this affect our estimate of the likelihood for life to develop on Earth-like planets (one of the variables in the Drake equation)?
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Most extrasolar planetary systems undoubtedly exist in an orientation that is *not* edge-on with respect to the Earth, thus the Doppler shifts that we measure in these systems are not a true measure of the orbital velocity of the star as it wobbles in response to its companion planet.
a) (2 pts) Will the Doppler shift amplitudes for systems *not* seen edge-on be larger or smaller than for systems seen edge-on? One-word answer is fine here.
b) (4 pts) Will the estimated masses (based on the measured Doppler shifts) for systems *not* seen edge-on be larger or smaller than for systems seen edge-on? Justify your answer with a brief sentence or reference to an appropriate equation.
c) (8 pts) We know Astronomers are biased in favor of detecting extrasolar planets with large masses and short periods. You do not need to explain why here. One could argue that Astronomers are *also* biased in favor of detecting edge-on systems over systems with any other kind of inclination. Explain why.
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Recently, a meteorite that landed in Antarctica several thousand years ago was found to perhaps contain traces of fossil life. The parent body of this meteorite was determined to be Mars. While it seems unlikely that a rock could be knocked off Mars and eventually find its way to Earth, some important evidence supports this claim.
a) (7 pts) Explain the evidence, contained in tiny pockets of gas inside the meteorite, that its parent body is Mars.
b) (7 pts) The meteorite appears to be a grey/black color while most of the surface of Mars is red. How do scientists explain the color difference?
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It was almost certainly necessary for Jupiter to form far from the Sun in order for it to grow to such a large size, yet we see other solar systems where Jupiter-sized planets exist close to their parent stars. In order for such a system to form, it seems that giant planets would have to form far away from their parent star, like Jupiter did, then spiral inward. Name and explain one possible mechanism that could stop this spiraling, leaving a giant planet very close to its parent star (we are left to wonder why this didn't happen in our solar system, of course).
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Suppose we construct a device to take spectra of a system of terrestrial planets in the future. If there are planets in another system that are very similar in all respects to Earth and Venus, state what spectral features of the two planets will be similar (at least one) and also state at least one spectral feature that will be different (and in a sentence explain why it is different).
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Recent discoveries of radial velocity variations in some stars have convinced some Astronomers that planetary companions must be orbiting these stars. Skeptics assert that many if not all of these systems may instead be systems where the companion is much more massive than a planet. Thus, we are looking at a series of binary star systems (in which the companion star is just too dim to observe directly) instead of a series of extrasolar planetary systems.
a) (7 pts) Explain why it might be possible that we are looking at binary star systems instead of planetary systems.
b) (7 pts) Explain how recent observations of a small dip in the apparent luminosity of a star (which shows these radial velocity variations) was used to help prove that it is a planetary system, not a binary star system.
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Recently, scientists have discovered a meteorite in Antarctica that may contain fossilized traces of life from Mars.
a) (6 pts) Explain briefly the conclusive evidence that tells us the meteorite in question truly originated on Mars rather than somewhere else.
b) (8 pts) Over 20 years ago, the Viking lander attempted to test for the existence of microbial life in the Martian soil. Explain what sort of control experiment was used at the time to discount the possibility that life really exists in the Martian soil today.
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A big discovery in the past year has been a star system in which a planetary companion not only makes the parent star wobble but also transits (or eclipses) the parent star periodically, resulting in a small predictable dip in the brightness of the parent star.
a) (7 pts) Explain briefly how we are able to deduce the mass and size (thus the density) of the companion planet.
b) (7 pts) Other non-transiting systems may not be planetary systems at all but rather binary star systems. Explain why this transiting system is the only extrasolar planetary system that we know about for sure and why the others might not be planetary systems.
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Recently, the search for ancient life on Mars has caused considerable excitement in the scientific community.
a) (4 pts) There is a meteorite that originated from Mars that appears to have fossilized microorganisms inside. Explain the conclusive evidence that shows this rock is indeed from Mars and not just some exotic Earth rock.
b) (4 pts) The Mars Odyssey mission has just arrived into orbit around Mars. Explain how this spacecraft will attempt to find a suitable landing spot for a future mission In where chances would be good of finding remnants of ancient life on Mars.
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One promising area in the search for extrasolar planets is the set of rare systems in which the companion planet transits in front of the parent star.
a) (4 pts) Explain why the discovery of the first transiting planet system is so important for extrasolar planet hunters (until then, it could be argued that no extrasolar planets had truly been found...as part of your answer, explain why).
a) (4 pts) A satellite named Kepler has been proposed which will observe over 100,000 sun-like stars. How will this satellite be able to detect extrasolar planets without using the Doppler shift technique? Explain.
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In the film "Life Beyond Earth", we found out about the possibility on life on other worlds and also got some perspective about intelligent life on our own.
a) (4 pts) On a 5-km "highway of life", what length accurately reflects all of recorded human history?
b) (4 pts) What recent evidence discovered in Antarctica implies that life may have once existed on Mars?
b) (6 pts) Which gas, oxygen or ozone, is probably a better indicator of the existence of life on another planet and why?
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Recently, a meteorite was discovered that may have traces of fossilized life. Explain why scientists believe that the meteorite originally came from Mars.
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Explain what many SETI scientists feel (based on the assigned reading) that all-sky survey-type searches will be more effective and likely to detect signals compared to very sensitive surveys targeting a limited number of stars.
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The Drake Equation has two possible extreme interpretations, a pessimistic and an optimistic interpretation as to the value of "N". Briefly explain arguments against each of these two extreme interpretations.
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Briefly explain three other techniques we currently use for finding extrasolar planets aside from the "Doppler wobble" technique.