Download Extrasolar Planets

Extrasolar Planets
extrasolar = outside of (external to) our
solar system
First, what is the difference between a star and a
planet?
How do we detect them?
How many are known?
Do any have life as we know it?
Here are some extrasolar planets – all artist
conceptions!
We are not yet able to image planets like this. Why?
Let s review our model solar system, week 1
If the orbit of the earth around
the sun is the size of the circle
out front, then:
•  the sun is the size of a big peach
•  the earth a very small seed, and the moon is about an inch away
•  Jupiter is a very small grape at the ramada
• Saturn is an even smaller grape, by the flagpole
Let s review our model solar system, week 1
If the orbit of the earth around
the sun is the size of the circle
out front, then:
The nearest star is in Chicago!
So we are trying to image a non-luminous grape near a very
bright peach from thousands of miles away
How can we discover planets?
1.  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
1. How might we image planets?
Telescope image of
Saturn, rings and
moons with a
SOHO spacecraft
coronagraph
image of the sun
with a coronagraph
?
Fomalhaut
HR 8799
Beta Pictoris
Combination of two near-infrared images
obtained with the Very Large Telescope
Techniques for finding extrasolar planets
2. Stellar Wobble
Review how gravity works: the space shuttle, the moon
around the earth
Is the sun influenced by the gravitational force
of the planets?
Does Jupiter orbit around the center of the sun?
Stars and planets orbit around
their center of mass
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
Note that the star is much brighter than the planet, so
we observe the motion of the star produced by the
planet. It also depends on the orientation of the star and
planet: face-on vrs edge-on
Turn to lecture tutorial, p. 125, Motion of Extrasolar planets
How do we observe stellar
wobble?
Remember the Doppler shift.
Looks
red
Looks
blue
What a plot of the data looks like
(Here s what the data actually look like)
We don t know the inclination of the
planet s orbit
Which one would show the largest Doppler wobble?
Suppose we observe some Doppler shift, v,
but we do not know the orientation of the
orbit. Which orbital orientation would imply a
larger mass planet?
A
B
The Doppler technique only
provides the minimum mass of
the planet if the orientation is
not known (which is most of the
time).
Techniques for finding extrasolar planets
3. Planetary Transit
Planetary Transit
Transit of sun by Venus
Last one occurred June 2012
Transits are easier to detect if
the planet is
(A) large
(B) small
What would you learn about a
planet if you found it with the
planetary transit technique?
(A) Its radius
(B) Its mass
(C) Its orbital period
(D) Both its radius and its orbital period
A special orientation is needed for a transit
Transits are rare
Transits get
(A) more
(B) less
likely as the planet s orbit
gets larger.
The Kepler Mission: this has discovered thousands of
planets
The WIYN telescope has confirmed many of the Kepler
discoveries
Review: The three extrasolar planet detection
techniques are:
1.  Direct imaging
2.  The “wobble” or “Doppler shift” technique
3. The transit method
Since about 1998, we have discovered thousands of
exoplanets. Almost all are around stars within about 300
light years of the sun.
What are extrasolar planets
like?
Are they similar to the planets in the solar
system? Class project on a comparison of our
solar system with some extrasolar systems.
http://www.astronomy.ohio-state.edu/~microfun/ob06109/
What defines life?
•  the capacity to grow,
•  metabolize (convert
food to energy)
•  respond (to stimuli),
•  adapt
•  reproduce
What is necessary? Recent discoveries of life under extreme conditions
on earth (extremophiles) show that neither sunlight nor oxygen are
required
1. How can we measure the number of stars in our galaxy?
(This isn’t an actual picture of
our galaxy. Why?)
Scientific Notation: or handling big numbers
scientific notation:
1,000
= 103 = one thousand
1,000,000 = 106 = one million
1,000,000 = 109 = one billion
100 = 102 1000 = 103 ,
102 x 103 = 105 (add the exponents)
(2 x 102) x (3 x 103) = 6 x 105
105 / 103= 102 (subtract the exponents)
Our CCD at 0.9m was 4 x 103 by 4 x 103 pixels. How many
pixels total?
yellowstone
Yellowstone National Park: microbes live in boiling
water (90 C). Other pools are extremely acidic, yet
microbes and bacteria thrive there
Life in extreme
conditions on
earth
Black smoker, deep in the
ocean: an example of life
that has no need of
sunlight:
From vents deep in the
ocean hydrogen sulfide
provide energy for
bacteria, which in turn
feed clams, tube worms
(up to 10 ft long)
The Drake Equation: statistical estimate of the
number of intelligent, communicating civilizations
in our galaxy right now
1.  Number of stars in our galaxy
2.  Fraction of stars that have planets around them
3.  Number of planets per star that are capable of supporting life (see
habitable zone)
4. 
5. 
6. 
7. 
Fraction of planets where life evolves
Fraction of these planets where intelligent life evolves
Fraction of intelligent life that communicates
Fraction of a planet’s lifetime during which the civilizations
communicate
N equals the product of all these factors!
how many left-handed, 8 year old boys are there is the US
right now?
1.  Population of the US, P:
2.  Fraction of males, Fm
3.  Fraction of people who are left handed Fl
4.  Fraction of population who are 8 years old F8
• 
Answer = P * Fm* Fl* F8