2nd Midterm

: Difficult Exam . . .

Common Mistakes 1. Greenhouse Effect: • CO2 absorbs IR light (not UV).

• 2. Geological activity on Jupiter’s moons is due to their composition of ice: Allows melting and flow at low temperatures in the outer solar system.

• 3. Titan retained its atmosphere because it’s cold: molecules don’t move fast enough to escape.

Announcements

•

Homework

due a week from Friday (May 2): • Read Chapter 13:

Planets Around Other Stars

•

Final Exam

- comprehensive: May 20 @ 8am: 237 Hearst Gym • Telescope Observations: - Observing Starts: 8pm !

- Sketch 2 Objects & Star Chart (3 obs of Mars): Due Friday, May 2 (w/ HW) !

"The Dawn of Creation: The First Two Billion Years"

A Special Lecture by

Steven Beckwith Wednesday, April 23, 5:30pm Chevron Auditorium International House

Be There !

Are there Other Planetary Systems ?

Are any of them like our Solar System ?

February 5, 1996

.

Now Exiting our Solar System to … .

The

.

. .

Milky Way Galaxy

. .

. .

Democritus:

Greek philosopher ( 460 - 370 BC ).

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“ There are innumerable worlds of different sizes.

These worlds are at irregular distances, more in one direction and less in another, and some are flourishing, others declining. Here they come into being, there they die, and they are destroyed by collision with one another. Some of the worlds have no animal or vegetable life nor any water. “

Epicurus (341-270 B.C.)

Greek philosopher in Athens where he opened a school of philosophy QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

“There are infinite worlds both like and unlike this world of ours ... we must believe that in all worlds there are living creatures and plants and other things we see in this world…”

Giordano Bruno 1584

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http://www.gospelcom.net/chi/DAILYF/2002/02/daily-02-17-2002.shtml

Wrote; ‘

De l'infinito, universo e mondi

(The Infinity, the Universe and Its Worlds) • Bruno was enthusiastic about the Copernican theory that the planets circle the sun and he believed there are many other planets around other stars, some of them with life. Giordano Bruno lost the thread of truth and the Roman Church burned him for it.

Burned at the Stake February 17, 1600 By Catholic Church

Stars are a billion times brighter…

…than the planet

hidden in the glare.

Detecting Earths: Like detecting a firefly next to a nuclear explosion

R

Light Reflected off Planet

Cross Sectional Area of planet:



r 2 r Fraction of Star light That hits planet: a)



r 2 / 4

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R 2 For Earth: Fraction is 10 -10 Area of Sphere: 4



R 2

Planet Detection

The Wobble of a Star: Gravitational pull by the planet Star moves slower, due to conservation of momentum: mass x velocity M STAR V STAR = M planet V planet

Wobble Velocity 1/2 m PL V PL 2 = G m PL M Star / r

V PL ~ 10 km/s

Momentum: V Star ( )

M STAR

V PL

V STAR ~ 10

m/s x (M PL /M JUP )

Spectrum starlight Detecting a Star’s Wobble: Doppler Effect

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Detecting the wobble of a Star, pulled around by its planet.

12 years . . . Jupiter

Need Telescope . . .

Quiz The period of the sine wave is: a) 2 day b) 10 day c) 20 day d) 40 day

Starlight From Telescope High Resolution ``Echelle”

Echelle Spectrometer

Echelle Grating

Collimator

CCD

4096 Pixels

Spectrum of Star:

Doppler Effect

Doppler Shift:

Dl/l

= v / c

Claim of First Detected Extrasolar Planet: 51Pegasi Orbital Period = 4.2 days ! Absurd

Michel Mayor & Didier Queloz 51 Peg QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

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One week Later . . . 4 Nights at Lick Observatory October 11, 1995

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Determination of Orbital Distance from Star to Planet Period = 4.2 days Kepler’s 3rd Law: P 2 = a 3 Units: P in years, a in AU Solve for a: a = 0.05 AU Proximity: Temp = 1500 C

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Determination of Planet’s Mass

Conservation of Momentum: momentum of star = momentum of planet M STAR V STAR = M planet V planet Solve for Mass of planet: M planet = M STAR V STAR / V planet M STAR : Star Masses are known (most are Sun-like) V STAR from Doppler shift: 55 m/s

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What is V planet ?

V planet = 2

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a / P You know “a” from Kepler’s 3rd Law: P 2 = a 3 Can Determine M planet

a b c d Quiz From Doppler measurements, a star exhibits the sine wave variation In velocity. The orbital plane is oriented edge-on to us at Earth, causing the planet to block the star light.

At what point on the velocity plot will the planet block the star light ?

Summary of Doppler Wobble Method

: Orbital Physics

Kepler’s 3rd Law and Conservation of Momentum P 2 = 4



2 /[G(M star + M planet )] a 3 P = orbital period a = orbital distance of planet from star Simple Version of Kepler’s 3rd Law: P 2 = 4

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2 /GM star a 3 ( planet’s mass is negligible compared to star.) Measure P from Doppler periodicity: Can solve for a.

Circular Orbit: V planet = 2

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a / P (Circumference/Time) Momentum Conservation: M star V star = M Planet V planet M planet = M star V star / V Planet

Doppler Wobble Method

: Unknown Orbital Inclination

Tilt of Planet’s Orbital Plane: Unknown

• Edge-on Orbit: Full Doppler Effect • Face-on Orbit: No Doppler Effect • General Tilt Angle: True Wobble speed is greater than Doppler indicates True planet mass is GREATER than the mass found by the Doppler method. (25% greater on Avg.)

We measure M sin i

51 Pegasi First Extrasolar Planet Period = 4.2 days Kepler’s 3rd Law: P 2 = a 3 Units: P in years, a in AU Solve for a: a = 0.05 AU Proximity: Temp = 1500 C

Detecting Extrasolar Planets

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Kepler’s 3rd Law: P 2 = a 3 Momentum Conservation: M STAR V STAR = M planet V planet

16 Cygni B

Mass = 1.7 M JUP (Min)

Not Sinusoidal Orbit Period 2.2 yr Velocity Wobble

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Orbit of Planet around 16 Cygni

16 Cygni: Planet & Moon

Life on Gas Giant Planets ?

Floaters Earth-Like Moon

Eccentric Orbit !

of Planet around 16 Cygni