Goal: To understand how we find Exo-Solar planets Objectives: 1)To learn what Hot Jupiters are and how we find them 2)To learn about the transit method 3)To learn about microlensing

What are hot Jupiters? 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!

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

First Discovery egon.edu/5 1peg.html

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)

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?

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.

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.

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

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

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.

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.

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)

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.

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

What is going on here?

Kepler 14-b (8.4 Jupiter masses)

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

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.

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.

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.

Current count As of planets BUT Kepler has 1200 candidates

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.