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?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!

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 1995

http://zebu.uoregon.edu/51peg.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.

• http://www.lpi.usra.edu/education/timeline/gallery/slide_1.html

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

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

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 11-22-2011

• 703 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.