1. A Search for Habitable Planets 1 NASA’s first mission to detect Earth-size planets orbiting in the habitable zone of sun-like stars. Launched March 6, 2009

2. A Search for Habitable Planets 2 How many Earths? How many Earth-size planets are in the habitable zone of sun-like stars? Credit NASA Goddard Space Flight Center http://visibleearth.nasa.gov/ By 2013... NASA’s Kepler mission will have an answer to this question!

3. A Search for Habitable Planets 3 Jupiter’s diameter is eleven times greater than the Earth’s, and it has over 300 times the mass. This is what we are looking for This is what we’ve found What have we found? The planets around other stars discovered so far are closer in mass to Jupiter.

4. A Search for Habitable Planets 4 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. Scientists use the Radial Velocity or “wobble” of a star to detect planets.

5. A Search for Habitable Planets 5 Size of Jupiter: 1% area of the Sun (1/100) 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. Kepler detectsTransits!

6. A Search for Habitable Planets 6 Let’s move this star away... Stars are far away …

7. A Search for Habitable Planets 7. Stars are far away …

8. A Search for Habitable Planets 8...and farther... Stars are far away …

9. A Search for Habitable Planets 9 Stars are far away …

10. A Search for Habitable Planets 10 Stars are far away …

11. A Search for Habitable Planets 11 Stars are far away …...and farther

12. A Search for Habitable Planets 12 Stars are far away …

13. A Search for Habitable Planets 13 Stars are very far away. We cannot see the planet cross in front of the star. Stars are far away …

14. A Search for Habitable Planets 14 Detecting Planets by Transits The Kepler Mission is designed to detect the slight dimming of the star when an Earth-size planet crosses between us and the star.

15. A Search for Habitable Planets 15 Detecting Planets by Transits Amount of light detected from the Star Jupiter-size planet? Earth-size planet?

16. A Search for Habitable Planets 16 For which of these star(s) will Kepler be able to detect transiting planets? A B C 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. System Orientation!

17. A Search for Habitable Planets 17 Where are we looking?

18. A Search for Habitable Planets 18 What is Kepler doing? 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%.

19. A Search for Habitable Planets 19 Its mission is to detect: orbiting in the habitable zone of sun-like stars. Earth-size planets

20. A Search for Habitable Planets 20 Why “Earth-size” planets? If a planet is: Too small (less than 1/2 the mass of Earth): Not enough gravity to hold onto a life- sustaining 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) Earth Mars Jupiter

21. A Search for Habitable Planets 21 What is the “Habitable Zone”? 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 SystemAnother sun-like star and its planets. Which planets are in its habitable zone? And its Habitable Zone

22. A Search for Habitable Planets 22 What is the “Habitable Zone” of a “sun-like” star? 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.

23. A Search for Habitable Planets 23 What is the “Habitable Zone” of a “sun-like” star? Cool Red stars: Less than the mass of the Sun Lifetime: Many billions to trillions of years Very small & close-in habitable zone

24. A Search for Habitable Planets 24 What is the “Habitable Zone” of a “sun-like” star? SUN-LIKE: Yellow/White Stars: 1 - 2 times mass of Sun Lifetime: Several billion years

25. A Search for Habitable Planets 25 What is the “Habitable Zone” of a “sun-like” star? HOT BLUE Stars: 3 - 60+ times mass of Sun Lifetime: Several million years Not enough time and too much radiation for life to evolve!

26. A Search for Habitable Planets 26 Comparative Life Zones of Stars

27. A Search for Habitable Planets 27 What else makes a planet “habitable”? 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.

28. A Search for Habitable Planets 28 What does an atmosphere do? It also matters if a planet has an atmosphere and how heavy that atmosphere is. “Sun” TOO HOT!TOO COLD! Mercury is too close to the Sun Venus’s “coat” is too heavy Earth is “just right” Mars is too far away and only lightly dressed!

29. A Search for Habitable Planets 29 How much of the Galaxy are we searching? Solar System here Image credit: NASA, STScI

30. A Search for Habitable Planets 30 How much of the Galaxy are we searching? Solar System here Image credit: NASA, STScI

31. A Search for Habitable Planets 31 How much of the Galaxy are we searching? Image credit: NASA, STScI Solar System here THIS MUCH !

32. A Search for Habitable Planets 32 Kepler would be searching an area about the size of Connecticut. Kepler Search Area Our whole Solar System would be this big Imagine, if you shrunk our solar system to a little larger than a quarter: How big an area is that? would span North America. Our Milky Way Galaxy

33. A Search for Habitable Planets 33 What’s next? When Kepler detects a possible Earth-size planet in the habitable zone of a sun-like star... Credit NASA Goddard Space Flight Center http://visibleearth.nasa.gov/ 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!

34. A Search for Habitable Planets 34 What else causes starlight to dim? Is it a planet that’s causing the star to dim? It might be an eclipsing binary: two stars orbiting each other, one passing in front of the other one. It might be a variable star that, for various reasons, normally gets brighter, then dimmer. LightLight

35. A Search for Habitable Planets 35 What is evidence of life? Look for evidence of oxygen Look for liquid water Look for signs of biological activity (methane) 17

36. A Search for Habitable Planets 36 More Information Kepler web site: http://Kepler.NASA.gov/ NASA’s Kepler Mission: Using transits orbiting in the habitable zone of sun-like stars. to detect Earth-size planets © 1999 Lynette Cook, all rights reserved.