Gravitational Microlensing

4 multiple choice question and 8 short answer essay questions

1. If we want to discover a Jupiter-sized planet orbiting at Jupiter's distance to a Sun-like star, which discovery technique would be most likely to find us the best candidate for obtaining a follow-up spectrum to learn more about its atmosphere?
   A. Astrometry
   B. Transit
   C. Radial Velocity
   D. Gravitational Microlensing
2. Which of the following is not evidence for the Nebular Model theory and the idea that our Solar System was formed from a once homogeneous mix of material?
   A. The composition of Carbonaceous Chondrite meteorites.
   B. Planets closer to the sun are more dense.
   C. HST observations of protoplanetary disks around young stars.
   D. The presence of an Oort Cloud.
3. You discover two planets orbiting a distant Sun-like star (Planet A & Planet B). Using the Transit Method, you determine the planets are both roughly 1.5 times the size of the Earth. Combining this with the Radial Velocity Method, you estimate the density of Planet A to be 0.99 g/cm3, and Planet B to be 5.3 g/cm3. Using this information, which planet would you expect to have a younger surface?
   A. Planet A's surface is younger.
   B. Planet B's surface is younger.
   C. I cannot determine the age based solely on this information.
   D. Both surfaces are the same age.
4. If Io and Europa formed farther from Jupiter than they are today, and remain in 2:1 resonance would the amount of geological activity on Io change?
   A. No, geological activity is driven by radioactive decay in the core, so it is independent of the distance to Jupiter.
   B. No, Io would still be just as active as before because the two satellites remain in resonance.
   C. Yes, because they are still in the same resonance so Io's orbit would still be elliptical.
   D. Yes, because Io is now further from Jupiter.
5. The cartoon below represents an asteroid in the asteroid belt

(4 pts) Describe the properties of this asteroid in the space provided below. Hint: Your argument should include information on the following: approximate size (in km); most likely composition (eg. ice, iron, cheese, etc.); possible sample type(s) (eg. meteorite classes) that would come from this asteroid.
(2 pts) Is it likely that this asteroid is differentiated? Explain your answer.

1. The figure below gives the reflectance spectra of five known surface samples: snow, live vegetation, dry soil, litter (a mix of dry soil and dead vegetation), and liquid water. The figure also includes spectra of two unknown surfaces: blue & green lines.

Using the information in the figure, answer the following three questions.

1. (4 pts) Describe the surface composition of the two unknown (blue & green) surfaces using the given samples.
2. (2 pts) If you had a camera with a narrow filter centered on 650 nm (+/- 10 nm) and that was the only part of the spectrum you could observe, would you be able to confidently distinguish the blue surface from a surface composed primarily of vegetation? Explain your response.
3. (2 pts) If you observe the green surface in only the visible wavelength region of the figure, would you conclude that there is snow on the green surface? Explain your response.
4. The image below is of a former comet after a very close encounter with one of the gas giant planets. The object passed within one planetary radius (1 Rplanet) of the planet.
5. (2pts) Describe where in the Solar System this comet likely came from?
6. (4 pts) Given the above information, describe the probable scenario and the mechanism responsible for leaving the comet in this disrupted state.
7. (1 pts) If the object were a 10 km asteroid, would it have suffered the same fate? Explain your response.
8. The surfaces of the satellites of the giant planets display a broad range of cratering histories. Their surfaces range from the heavily crater-saturated to the smooth and nearly pristine. A variety of mechanisms are responsible for these differences. Take for example Triton, Neptune’s largest satellite:

Its surface has a little of everything: heavily cratered regions, smooth surfaces and some interesting features rarely seen on other worlds in the Solar System. The most unique features are the dark streaks located near Triton’s southern pole as seen in the above image. In the space below, answer the following three questions.

1. (4 pts) What are these dark streaks and where did they come from? Hint: Describe the mechanism that created these features and also mention whether this mechanism is still modifying the surface today.
2. (2 pts) Discuss briefly another world likely to have the same mechanism at work, explaining why these two worlds would be affected by this same phenomenon.
3. (2 pts) Finally, would it be possible for you to determine the surface ages (relative or absolute) of either Triton, or the world you discussed above? Explain why or why not.
4. Our planetary system may be unusual in having a giant planet like Jupiter, and yet Jupiter has had an enormous impact on the formation, evolution and components of our Solar System.
   Provide 3 examples of how Jupiter may have influenced our Solar System’s history, structure and/or habitability.
   For each example, describe what Jupiter influenced, and also how Jupiter was responsible.
5. It’s the year 2040, and NASA’s LUVEx telescope, a space-based direct imaging telescope with a coronagraph, has (finally!) launched. During its initial year of operation it has sent back the first direct imaging spectra of extrasolar terrestrial planets from three different planetary systems. Each planet was observed at both visible (left) and mid-infrared (right) wavelengths (LUVEx won’t be able to observe the mid-infrared, but let’s just pretend it can for the duration of this question :) ). Examine the spectra of the three planets below (and the atmospheric molecules they reveal) and answer the following questions. Note that masses of the planets (in Earth masses) are also given in the left of the diagram.
6. (4 pts) Which of the three planets, A, B or C is most likely to be habitable? Why? Justify your choice by also explaining why the other two planets are not likely to be habitable.
7. (2 pts) Which of these planets is most likely to have life on it? Justify your answer by describing biosignatures detected in the spectra of the planet.
8. (2 pts) Carbon dioxide is generally not considered a reliable sign of life when detected in the atmosphere of a planet. However, there is one scenario in which it might be a biosignature. What is that scenario, and how would you use LUVEx to detect it?
9. The Nobel-prize winning discovery in 1995 of 51 Peg b, a Jupiter-sized planet orbiting the Sun-like star 51 Pegasus in a 4.2 day orbit, revolutionized our understanding of the possibility of extrasolar planets. It also really changed our thinking about our own solar system and the key processes that sculpted it. Explore the broader impact of 51 Peg b on our understanding of our own Solar System by answering the questions below. Keep your answers brief.
   (2 pts) Which technique was used to discover the planet 51 Peg b? Describe how this technique was able to detect the planet.
   (1 pt) Give two reasons why 51 Peg b was more likely to be detected by this particular technique.
   (2 pts) Given what you know about the condensation sequence and the core accretion method of planet formation, explain why no one expected to find 51 Peg b so close to its star.
   (1 pt) Given what you know about giant planet atmospheres and atmospheric escape, why is it perfectly OK for 51 Peg be to be so close to its star?
   (1 pt) How did the discovery of 51 Peg b change our thinking about a key process that planets undergo after formation that we might have mistakenly ignored in our own solar system?
   (3 pts) Based on this change in our understanding, briefly describe (1-2 sentences) one theory of the past evolution of our solar system inspired by the discovery of 51 Peg b that helps us better explain a key observable about our Solar System, and describe that observable.
10. Make a scientific case for why Europa may be an excellent place to look for life beyond the Earth. To answer this question:
11. (1pt) List life's three requirements for a habitable environment
12. (1pt) Describe our current understanding of the components of Europa’s internal structure
13. (4pts) Describe two observations of Europa that provide evidence that the world likely meets at least one of those requirements, and explain how those observations support the case for Europa’s habitability
14. (2pts) Describe a key planetary process that could deliver energy to Europa, and explain how this process enhances Europa’s potential habitability.

Sample Solution