Goal: To understand how we find Exo-Solar planets

1. Goal: To understand how we find Exo-Solar planets Objectives: To learn what Hot Jupiters are and how we find them To learn about the transit method To learn about microlensing

2. What are hot Jupiters?http://www.theregister.co.uk/2008/12/10/nasa_co2_gas_giant/ • Gas giants • Very close to their star • Very short orbital periods • Very hot on one side • Tidally locked to the star? • Not in the gas giant region!

3. Problem: • Stars are billions of times brighter than planets. • Using normal telescopes and normal viewing methods spotting a planet directly is very improbable.

5. First Discovery 1995 http://zebu.uoregon.edu/51peg.html

6. Why do we find so many Hot Jupiters? • The bigger the planet the more it moves the star it orbits • The closer to the star the shorter the orbital period • The closer to the star the faster the star moves • (gravity depends on the inverse of the distance squared)

7. How are Hot Jupiters formed? • You cannot form a gas giant that close to a star. • It had to form elsewhere and moved there. • But how?

8. Back to the beginning • We start out with a protostar and a disc • We form a 10 earth mass core • We get run away accretion as the massive core eats up all the gas in its path and becomes a gas giant.

9. For Hot Jupiters: • Once they have eaten up all the materials in their orbit you will have a dark empty ring in the disc. • At this point the planet has gained enough mass that the length of its gravitational reach increases enough to gobble up the material around it. • http://www.lpi.usra.edu/education/timeline/gallery/slide_1.html

10. Side effects • If it only gobbles materials outside of it (that is it takes material and moves it in towards itself) then it has to move out. • If gobbles on inside then it would move inward

11. Planetary migration • If a planet gobbles form the inside and outside the net effect will be very small. • However, if you have multiple planets…

12. Planetary Migration slide 2 • Once the material between 2 planets is consumed the outer planet can only eat what is outside of it and will move out. • The inner planet will eat the material inside of it as it moves in.

13. Evolution to Hot Jupiter • As the planet moves in it is closer to material that was previously too close. • It is also now larger and will eat that material as well. • This will produce a run away effect that only ends when the gas giant either gets very close to the star or the protostar turns into a full star and blasts out the remaining gas into deep space.

14. Effects on Terrestrial Planets • There are some models that predict that after the gas giant passes that the disc can be repopulated with the gas giants expelled leftovers • However it is more likely that the forming terrestrial planets are either: • 1) eaten by the gas giant • 2) pushed into the star • 3) flung into the outer solar system (similar to Oort cloud objects)

15. The question remains • Are we the exception to the rule? • 1) Hot Jupiters could be common. • 2) This could be an artifact of the fact that it is just easy to find them.

16. Transit/Eclipse Method • Works for planets just like for stars • Planet in front of star, it eclipses the star, barely • Jupiter in front of our sun would make it 1% dimmer • Need to have an inclination very close to 90 degrees

18. What is going on here?

19. Kepler 14-b (8.4 Jupiter masses)

20. Microlensing • Using gravity from a star/planet as a lens for a background star • From the intensity and duration of the lensing you can find the mass and size of the objects doing the lensing

23. http://planet.iap.fr/OB05390.news.html

24. What we can determine • The amount of brightening of the background star tells you the mass of the planet • The time period between peaks tells you the distance between planet and its star.

25. Advantages • No longer dependant on the distance to the star! • We can now find objects that are further out without taking decades to do it. • Can find earth sized planets using this method • Can find planets in stars very far from our sun.

26. Problems • This is a luck based procedure • It is a one shot proposition • Can only be done for certain parts of the sky which means for certain parts of our galaxy. • The planets found are so far away that we cannot study them anytime soon. • In fact we might not be able to see the star they orbit.

27. Current count • As of 11-22-2011 • 703 planets • BUT Kepler has 1200 candidates

28. Conclusion • We have learned how Hot Jupiters form • We have examined the implications of having a Hot Jupiter in a solar system • We have learned the possible fates of a Hot Jupiter.