Exoplanets:Finding Other Worlds Around Other Stars

Paul GreenCenter for Astrophysics

• What's the nearest star?

• Different kinds of stars• hot and cool• large and small• far and near

• Difference between a star and a planet?• Stars shine, planets don't• So why can we see planets?

• There are different kinds of planets too!

Our Solar System

(Comparing Sizes)

Terrestrial (Rocky) Planets

Gas Giant Planets

Planets’ Distances from the Sun

How the Solar System FormedAbout 5,000,000,000 years ago

Why do you think the rocky planetsare close to the Sun, and the gas giants far away?

Exoplanets

Do you think there are planets around other stars?

Finding Exoplanets

Like a mosquito near a far away headlight, planets around other stars are too faint to be seen.

So how can we find them?

TIME

BRIGHT

NESS

00

Imagine you have a light sensor aimed a lamp.

What would the transit of a book look like if you made a graph of brightness vs time?

Like this?

TIME00

BRIGHT

NESS

What would the transit of a planet look like if you made a graph brightness vs

time?

TIME00

BRIGHT

NESS

TIME00

This is a “light curve.”

How are the planet’s size and orbital period

shown in the light curve?

BRIGHT

NESS

What’s This?

NASA’s Kepler Mission

A Kepler Planetary Transit Lightcurve

3.2 day period

5 hour eclipse

21

Transiting Planets pre-Kepler

Orbital Period in days

Size

Rel

ative

to E

arth

2222

Transiting Planets as of June 2010Data: May-Sep 2009

Orbital Period in days

Size

Rel

ative

to E

arth

Jun 2010

23

Transiting Planets as of Feb 2011Q0-Q5: May 2009 - Jun 2010

Orbital Period in days

Size

Rel

ative

to E

arth

Jun 2010 Feb 2011

24 Orbital Period in days

Size

Rel

ative

to E

arth

Transiting Planets as of Dec 2011Q0-Q6: May 2009 - Sep 2010

Jun 2010 Feb 2011 Dec 2011

Different Types of Stars

Do blue stars always look fainter than red stars?

28

What’s Next?• Kepler has discovered thousands of planets, now what?

• There are big surprises, like gas giants in close orbits,and enormous super-earths in large orbits.

• Time to search for signs of life!

• Giant telescopes are being built right now!

Habitable Zone