Transcript Goal: To understand how Saturn formed and what its core is

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.uor
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.
•
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.