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Journal 2/15/17 What requirements did we say were necessary for life? How would we look for those in other star systems? Objective Tonight’s Homework To learn about regions around stars that can support human life Check your system for planets within the habitable zone The Habitable Zone When we look at other star systems, one of the first things we look for is what’s called the “habitable zone”. This is the area in the star system where you’d be just the right distance for water to be liquid. Why? Because it might mean a planet like Earth that we could someday colonize. So what factors influence the temperature of a planet? (Let’s make a list as a class) The Habitable Zone For purposes of this class, we’re only going to deal with 2 factors for finding habitable zone: distance and atmosphere. There are dozens of very complex equations to find this sort of thing, but Mr. C. has done some math and is boiling everything you need down to the simple equation below: Distance (in AU) = 73,632 ( L _ ½ (T-30)4 ) Or, rearranged… Temperature (in Kelvin) = 271.35 L ¼ + 30 D2 ( ) The Habitable Zone Example: Find the habitable zone range for the sun. The Habitable Zone Example: Find the habitable zone range for the sun. We want to use the first equation as it will tell us distances given temperatures. We said the habitable zone is where the temperature would give liquid water. Liquid water exists between 273 and 373 kelvin. So all we have to do is plug those in to get our range. Distance (close) = 73,632 1 _ ½ (373-30)4 ( Distance (close) = 73,632 Distance (close) = 0.63 AU ) ½ (7.22e-11) The Habitable Zone Example: Find the habitable zone range for the sun. 1 _ ½ Distance (far) = 73,632 (273-30)4 ( ) ½ -10 (6.86e ) Distance (far) = 73,632 Distance (far) = 1.25 AU So for an earth-like planet with an atmosphere like ours, we can expect to find liquid water at any distance between 0.63 AU and 1.25 AU. Earth is at 1 AU, so this makes sense! The Habitable Zone Problems with this idea: We have a few places in our own solar system that are outside the habitable zone but could still have liquid water. Like Europa. The major problem with the calculations for the habitable zone is that they don’t take any odd factors into account. Like tidal stretching, volcanic activity, or ultra-thick atmospheres. We have to keep in mind that this model is just an estimate. Habitable Zone Diagram We’re going to do an activity where you find the habitable zone range for each of the 7 major kinds of stars. Mr. C. is going to give you a handout. On the handout, find the close and far range for each type of star, given their luminosities (replace L with each star’s luminosity). This will tell you where liquid-water planets can be found for each kind of star. Exit Question As a star gets bigger and brighter, its habitable zone will move.... a) Farther from the star b) Closer to the star c) It depends d) None of the above