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Journal 2/9/17 What's the most alien kind of planet you can think of? Try to come up with something realistic, but super-different from anything in our solar system! Objective Tonight’s Homework To learn how we find planets around other stars Read Nightfall pp 1-7 Detecting Extrasolar Planets History and Detection: The first exosolar planet was found in 1995 around the star 51 Pegasi. The planet is 150 times more massive than Earth but orbits at 1/10 the distance mercury does from our own Sun. The planet is designated “51 Pegasi b” but has unofficially been named “Bellerophon”. Detecting Extrasolar Planets Since then, we’ve confirmed the discovery of over 1,500 3,400 planets orbiting around other stars. But how do we detect them? We have 3 methods: - Spectroscopy (red and blueshift like how we detect binary stars.) - Transit (when the planet goes in front of the star, dimming it like a binary light curve.) - Microlensing (when gravity from the system can act like a lens, bending light around to magnify possible planets in the system.) Detecting Extrasolar Planets The spectroscopic and transit methods are the most successful, so we’ll discuss those. When we look at a star, it’s possible to see some very slight variations in the light curve. Since planets go around stars only slowly, this observation is usually over a period of years. If we see slight variation, it could indicate a planet making the star move and wobble a bit. years of time Detecting Extrasolar Planets We can use a similar method for spectroscopy. If we see the star wiggle between red and blueshift over a period of years, we know planets must be orbiting the star. Determining the properties of a planet based on these methods is far harder. After all, if we see a wiggle, what does that tell us? Scientists have managed to get approximate size, distance, and temperature of a planet from such wiggles! Detecting Extrasolar Planets We also have bias in the planets we find. Most extrasolar planets are found around smaller stars (G, K, and M classes). The planets we find are also usually huge Jupiter-like planets. This is mainly for two reasons: 1) Larger stars emit more radiation. This makes it harder for planets to form because the light from the star pushes away rocks and debris needed to make planets. 2) Our instruments for detecting planets are sort of crude. Because of this, we only really see the big ones since they’re more visible. There are likely tons of small planets we just can’t detect yet. Detecting Extrasolar Planets Even with this bias, we’re finding a lot of planets. Astronomers estimate that on average, there are about as many planets in the galaxy as stars. This means there could be 400 billion planets in our galaxy! Homework Time Your homework for this week is to read an award-winning science fiction short story called “Nightfall”. It’s about a civilization on a planet with 6 stars. It’s a pretty cool story. Pages 1-7 are assigned for tonight, but you’re more than welcome to read ahead. Exit Question True or false: the majority of planets we’ve seen, we’ve observed directly with telescopes. a) true b) false