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?

SOHO spacecraft image of the sun with a coronagraph

?

Telescope image of Saturn, rings and moons with a coronagraph

Fomalhaut

HR 8799

Beta Pictoris

Combination of two near-infrared images obtained with the Very Large Telescope

2. Stellar “Wobble”

Techniques for finding extrasolar planets

Is the sun influenced by the gravitational force of the planets?

Does Jupiter orbit around the center of the sun?

Review how gravity works: the space shuttle, the moon around the earth

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?

A B C D

Size of sun, Jupiter roughly to scale.

Sizes and distances not to scale with each other.

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).

3. Planetary “Transit”

Techniques for finding extrasolar planets

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.  Fraction of planets where life evolves 5.  Fraction of these planets where intelligent life evolves 6.  Fraction of intelligent life that communicates 7.  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