1. extrasolar = outside of (external to) our solar system
Extrasolar Planets
extrasolar = outside of (external to) our solar system

2. How can we discover planets?
Try to image them
2. Observe the motion of the star as it gets pulled by the
planet
3. Look at stars and wait for planets to go in front of them,
making the stars temporarily dimmer

3. 1. Imaging Techniques for finding extrasolar planets
This is very hard to do because the light from the planet is extremely dim compared to the host star and the planet is close to the star.
Therefore need to somehow mask the light from the star

4. Can you think of a way around the problem?
SOHO spacecraft
image of the sun
with a coronagraph
Are these real?
Why can’t we see planets?

5. Beta Pictorisa
Combination of two near-infrared images obtained with the Very Large Telescope

6. It is difficult to directly image planets
It is difficult to directly image planets. Only a few planets have been detected with this method. In general, this technique can discover extended disks around stars that are likely in the process of forming a planetary system
Are these real?
Why can’t we see planets?

7. Techniques for finding extrasolar planets
2. Stellar “Wobble”

8. Is the sun influenced by the gravitational force of the planets?
Does Jupiter orbit around the center of the sun?

9. Suppose Jupiter and the Sun could be placed on a see-saw
Suppose Jupiter and the Sun could be placed on a see-saw. Which point is closest to the center of balance?
Size of sun, Jupiter roughly to scale.
Sizes and distances not to scale with each other. A B C D

11. Now, how do we observe this wobble?

12. How do we observe stellar wobble?
Draw on the board here: planet moves, but does sun also move? Yes.
And explain the Doppler shift.
(Here’s what the data actually look like)

13. The first planets were detected with this method, and to date, hundreds of planets have been detected with this method. Before 2009, nearly all planets were detected with this method.
Are these real?
Why can’t we see planets?

14. Techniques for finding extrasolar planets
3. Planetary “Transit”

15. A special geometry is needed for a transit Transits are rare

16. The Kepler Mission

17. The Kepler mission has now discovered thousands of planets using the transit technique primarily – search is biased towards detecting low mass planets

20. The Kepler Mission
Has greatly increased the possibility that life exists on other planetary surfaces