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Structure PH116: of the Universe 1-5: 1 point each 6, 7, & 8: 5 points each 1. What method has detected the most extrasolar planets so far? a. b. c. d. The transit method Hubble images The Doppler method The Astrometric method Homework 1, due Thursday 29 January 7. The planet orbiting TrES-1 has been detected by both the transit and Doppler methods, so we can calculate its density and get an idea of what type of planet it is. a. Using the method of Mathematics Insight 13.3, calculate the radius of the transiting planet. The planetary transits block 2% of the star's light. The star TrES-1 has a radius of about 85% of our Sun's radius. b. The mass of the planet is approximately .75 times the mass of Jupiter, and Jupiter's mass is about 1.9X10^27 kg. Calculate the average density of the planet. Give you r answer in grams per cubic centimetre. Compare this density to eh average desity of Saturn (.7 g/cm^3) and Earth (5.5 g/cm^3). Is the planet terrestrial or jovian in nature? 8. It's possible to make a rough estimate of how often planetary systems form by making some basic assumptions. For example, if you assume that the stars we see have been born at random times over the last 10 billion years, then the rate of star formation is simply the number of stars we see divided by 10 billion years. The fraction of planets with detected extrasolar planets is at least 5%; so this factor can be multiplied in to find the approximate rate of formation of planetary systems. a. Using these assumptions, how often does a planetary form system in out galaxy? (our galaxy contains at least 100 billion stars) b. How often does a planetary system form somewhere in the observable universe, which contains at least 100 billion galaxies? c. Write a few sentences describing your reaction to your results. Do you think the calculation is realistic? Are the rates larger or smaller than you expected? 2. How many extrasolar planets have been detected? a. b. c. d. e. 1-10 10-50 50-250 500-1000 More than 10,000 3. Which one of the following can the transit method tell us about a planet? a. b. c. d. Its mass Its size The eccentricity of its orbit Its age 4. Which method could detect a planet in an orbit that is face-on to the Earth? a. Doppler method b. Transit Method c. Astrometry 5. How is the planet 51 Pegasi b different from Jupiter? a. Much closer to its star b. Much longer year c. Much more massive 6. How hard would it be for and alien astronomer to detect the light from planets in out solar system compared to light from the sun itself? a. Calculate the fraction of the total emitted sunlight that is reflected by Earth. What fraction of that area does the disk of a planet take up? Note Earth's reflectivity is 29%. (imagine a sphere around the sun the size of the planet's orbit) b. Would detecting Jupiter be easier or harder than detecting Earth? Comment on whether you think Jupiter's larger size or greater distance has a stronger effect on its detectability. You may neglect any difference in reflectivity between Earth and Jupiter.

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