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A Search for Habitable Planets NASA’s first mission to detect Earth-size planets Launched March 6, 2009 orbiting in the habitable zone of sun-like stars. 1 How many Earths? A Search for Habitable Planets How many Earth-size planets are in the habitable zone of sun-like stars? NASA’s Kepler mission will have an answer to this question! By 2013 . . . Credit NASA Goddard Space Flight Center http://visibleearth.nasa.gov/ 2 What have we found? The planets around other stars discovered so far are closer in mass to Jupiter. A Search for Habitable Planets This is what we’ve found This is what we are looking for Jupiter’s diameter is eleven times greater than the Earth’s, and it has over 300 times the mass. 3 Scientists use the Radial Velocity or “wobble” of a star to detect planets. A Search for Habitable Planets If an unseen planet tugs the star back and forth… Astronomers can detect these shifts by very carefully observing the spectra (or colors) of the stars. This method has revealed many stars with large planets, but is not quite sensitive enough to detect Earth-size planets. 4 Kepler detectsTransits! Size of Jupiter: 1% area of the Sun (1/100) A Search for Habitable Planets Size of Earth or Venus: 0.01% area of the Sun (1/10,000) A transit occurs when a planet crosses the line of sight between an observer and a star and blocks a small amount of light from the star, causing the light from the star to dim slightly for a few hours. 5 Stars are far away … A Search for Habitable Planets Let’s move this star away . . . 6 Stars are far away … A Search for Habitable Planets . 7 Stars are far away … A Search for Habitable Planets . . .and farther . . . 8 Stars are far away … A Search for Habitable Planets 9 Stars are far away … A Search for Habitable Planets 10 Stars are far away … A Search for Habitable Planets . . .and farther 11 Stars are far away … A Search for Habitable Planets 12 Stars are far away … A Search for Habitable Planets Stars are very far away. We cannot see the planet cross in front of the star. 13 Detecting Planets by Transits A Search for Habitable Planets The Kepler Mission is designed to detect the slight dimming of the star when an Earth-size planet crosses between us and the star. 14 Detecting Planets by Transits Amount of light detected from the Star A Search for Habitable Planets Earth-size planet? Jupiter-size planet? 15 System Orientation! A Search for Habitable Planets For which of these star(s) will Kepler be able to detect transiting planets? B A B. The star’s planets must orbit the star edge-on from our viewpoint! Not all planetary orbits are aligned this way . . . So we must watch thousands of stars to find several that are correctly oriented. C 16 Where are we looking? A Search for Habitable Planets 17 What is Kepler doing? A Search for Habitable Planets Launch: March 6, 2009 Continuously and simultaneously monitoring about 100,000 stars for at least four years in an area 10 by 10 degrees of sky. To detect two or more orbits of each planet orbiting in the habitable zone of sun-like stars. The probability that a planet in the habitable zone is aligned properly to transit the star is about 0.5%. 18 A Search for Habitable Planets Its mission is to detect: Earth-size planets orbiting in the habitable zone of sun-like stars. 19 Why “Earth-size” planets? A Search for Habitable Planets If a planet is: • Too small (less than 1/2 the mass of Earth): Earth Mars Not enough gravity to hold onto a lifesustaining atmosphere (like Mercury or Mars) • Too big (More than about 10 times the mass of Earth): Holds onto too much of the light gases (hydrogen and helium) and turns into a giant (like Jupiter or Neptune) Jupiter 20 What is the “Habitable Zone”? A Search for Habitable Planets Where evidence of life might be detected across the vastness of space: An orbit around a star where liquid water might exist on the planet’s surface year-round. Our Solar System And its Habitable Zone Another sun-like star and its planets. Which planets are in its habitable zone? 21 What is the “Habitable Zone” of a “sun-like” star? A Search for Habitable Planets On a cold night, how close would you stand to be comfortable? These different sized fires represent different sizes of stars. More massive stars are hotter stars! Mass determines temperature and lifetime of the star. 22 What is the “Habitable Zone” of a “sun-like” star? A Search for Habitable Planets Cool Red stars: Less than the mass of the Sun Lifetime: Many billions to trillions of years Very small & close-in habitable zone 23 What is the “Habitable Zone” of a “sun-like” star? A Search for Habitable Planets SUN-LIKE: Yellow/White Stars: 1 - 2 times mass of Sun Lifetime: Several billion years 24 What is the “Habitable Zone” of a “sun-like” star? A Search for Habitable Planets HOT BLUE Stars: 3 - 60+ times mass of Sun Lifetime: Several million years Not enough time and too much radiation for life to evolve! 25 Comparative Life Zones of Stars A Search for Habitable Planets 26 What else makes a planet “habitable”? A Search for Habitable Planets Would it matter if you wore a light jacket? How about a very heavy jacket? It also matters if a planet has an atmosphere and how thick that atmosphere is. 27 What does an atmosphere do? A Search for Habitable Planets TOO HOT! “Sun” Mercury is too close to the Sun TOO COLD! Venus’s “coat” is too heavy Earth is “just right” Mars is too far away and only lightly dressed! It also matters if a planet has an atmosphere and how heavy that atmosphere is. 28 How much of the Galaxy are we searching? A Search for Habitable Planets Solar System here Image credit: NASA, STScI 29 How much of the Galaxy are we searching? A Search for Habitable Planets Solar System here Image credit: NASA, STScI 30 How much of the Galaxy are we searching? A Search for Habitable Planets THIS MUCH ! Solar System here Image credit: NASA, STScI 31 How big an area is that? Imagine, if you shrunk our solar system to a little larger than a quarter: Our whole Solar System Our Milky Way Galaxy A Search for Habitable Planets Kepler Search Area Kepler would be searching an area about the size of Connecticut. would be this big would span North America. 32 What’s next? A Search for Habitable Planets When Kepler detects a possible Earth-size planet in the habitable zone of a sun-like star . . . Follow-up work is done by other methods to make sure it’s really a planet . . . . . . and other observations try to detect evidence of life! Credit NASA Goddard Space Flight Center http://visibleearth.nasa.gov/ 33 What else causes starlight to dim? A Search for Habitable Planets Is it a planet that’s causing the star to dim? It might be a variable star that, for various reasons, normally gets brighter, then dimmer. L i g h t It might be an eclipsing binary: two stars orbiting each other, one passing in front of the other one. 34 What is evidence of life? A Search for Habitable Planets Look for evidence of oxygen Look for liquid water Look for signs of biological activity (methane) 1735 More Information NASA’s Kepler Mission: Using transits A Search for Habitable Planets to detect Earth-size planets orbiting in the habitable zone of sun-like stars. Kepler web site: http://Kepler.NASA.gov/ © 1999 Lynette Cook, all rights reserved. 36