lecture_tan36 - Key Concepts Lecture 36 The Search for...

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Key Concepts: Lecture 36: The Search for Planets and Life Transit Technique The Habitable Zone Estimates from Drake Equation SETI and Fermi’s Paradox Planet Search Techniques Planet Searches: (Many more extrasolar planets are now known than there are planets in our own solar system) 1. Radial velocity search: gravity of planet causes star to wobble. Look for the blue and redshift of spectral lines from the star Most sensitive to massive planets that are close to their stars detected >~500 planets to date 2. Transit Search A planet passes in front of its star. We see a small dip in the brightness of the star. If we know the size of the star, we can then measure the size of the planet. Depth of Transit Depends on Relative Sizes of Star and Planet • Transit search technique measures the size of the planet (if we already know the size of the star)
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First Planetary Transit Detected in year 1999 • Star is called HD209458 • Radius of planet is 1.3 times Jupiter’s radius • Mass of planet (from radial velocity technique) is 0.63 times Jupiter’s mass • Why is the planet so big? Probably because it is so close to its star, is strongly heated, and so is puffed up. 3. The Microlensing Technique Microlensing is when a star (the Lens star) passes in front of a background star (the Source star) and acts as a gravitational lens, bending the light to our telescopes (recall Einstein’s General Relativity). This causes the source star to appear to brighten and then fade over time (see fig. on right). If the lens star has a planet, this can cause an extra blip in the magnification. This method is good at finding small planets that are far from their star (in contrast to the radial velocity method). But it requires monitoring millions of source stars and generally the planets that are found are so far away from us they are difficult to study further with other techniques. 4. Direct Detection
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This note was uploaded on 09/07/2011 for the course AST 1002 taught by Professor Dr.haywoodsmith,jr during the Spring '07 term at University of Florida.

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lecture_tan36 - Key Concepts Lecture 36 The Search for...

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