2nd Midterm: Difficult Exam... Common Mistakes 1. Greenhouse Effect: CO2 absorbs IR light (not UV)....
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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.
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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) !
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Wednesday, April 23, 5:30pmChevron Auditorium - International House
"The Dawn of Creation: The First Two Billion Years"
A Special Lecture by
Steven Beckwith
Be There !
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Are there Other Planetary Systems ?Are there Other Planetary Systems ?
Are any of them Are any of them
like our Solar System ?like our Solar System ?
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February 5, 1996
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Now Exiting our Solar System to …Now Exiting our Solar System to …
The Milky Way Galaxy. .. . ..
. .. . . .. .
..
. . ..
. . ..
..
Now Leaving our Solar System . . .
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Democritus:Greek philosopher (460 - 370 BC).
“ 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. “
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Epicurus (341-270 B.C.)
“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…”
Greek philosopher in Athens where he opened a school of philosophy
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• 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.
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Giordano Bruno 1584
Giordano Bruno lost the thread of truth and the Roman Church burned him for it.
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)
Burned at the Stake February 17, 1600
By Catholic Church
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Stars are a billion times brighter…
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…than the planet
hidden in the glare.
Detecting Earths: Like detecting a firefly next to a nuclear explosion
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Light Reflected off Planet
Area of Sphere: 4 R2
Cross Sectional Area of planet: r2
Fraction of Star lightThat hits planet:
a) r2
R
/ 4 R2
For Earth: Fraction is 10 -10
r
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Planet DetectionPlanet Detection
The Wobble of a Star:The Wobble of a Star:
Gravitational pullGravitational pullby the planetby the planet
Star moves slower, due to Star moves slower, due to conservation of momentum: mass x velocityconservation of momentum: mass x velocity
MMSTARSTAR V VSTARSTAR = M = Mplanetplanet V Vplanetplanet
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1/2 m1/2 mPLPLVVPLPL2 2 == G mG mPLPLMMStarStar / r / r
VVPL PL ~ 10 ~ 10 km/skm/s
VVStarStar = = VVPLPL VVSTARSTAR ~ 10 ~ 10 m/sm/s xx (M(MPLPL /M /MJUPJUP))
Momentum:Momentum:
WobbleWobbleVelocityVelocity
MMPLPL
MMSTARSTAR
( )
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Detecting a Star’s Wobble: Detecting a Star’s Wobble: Doppler EffectDoppler Effect
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Detecting the wobble Detecting the wobble of a Star, pulled of a Star, pulled around by its planet.around by its planet.
SpectrumSpectrumstarlightstarlight
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12 years12 years . . . Jupiter . . . Jupiter
(Met
ers/
sec)
Need Telescope . . .
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Quiz
The period of the sine wave is:
a) 2 dayb) 10 dayc) 20 dayd) 40 day
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Echelle Spectrometer
CCD
Echelle
Grating
Collimator
StarlightStarlight
From TelescopeFrom Telescope
High Resolution ``Echelle”High Resolution ``Echelle”
SpectrometerSpectrometer
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Spectrum of Star:Spectrum of Star:
Doppler EffectDoppler Effect
Doppler Shift:Doppler Shift: = v / c= v / c
4096 Pixels
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Michel Mayor & Didier Queloz
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51 Peg
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Claim of First Detected Extrasolar Planet:Claim of First Detected Extrasolar Planet:5151PegasiPegasi
Orbital Period = 4.2 days ! Absurd Orbital Period = 4.2 days ! Absurd
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One week Later . . .
4 Nights at Lick Observatory
October 11, 1995
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Period = 4.2 days
Kepler’s 3rd Law: P2 = a3
Units: P in years, a in AU
Solve for a:a = 0.05 AU
Proximity: Temp = 1500 C
Determination of Orbital Distance from Star to Planet
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Determination of Planet’s Mass
Conservation of Momentum: Conservation of Momentum: momentum of star = momentum of planetmomentum of star = momentum of planet
MMSTARSTAR V VSTARSTAR = = MMplanetplanet V Vplanetplanet
Solve for Mass of planet:Solve for Mass of planet:MMplanetplanet = M = MSTARSTAR V VSTARSTAR / V / Vplanetplanet
MSTAR : Star Masses are known (most are Sun-like)
VSTAR from Doppler shift: 55 m/s
What is Vplanet ?
Vplanet = 2 a / PYou know “a” from Kepler’s 3rd Law: P2 = a3
Can Determine Mplanet
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Quiz
From Doppler measurements, a star exhibits the sine wave variationIn velocity. The orbital plane is orientededge-on to us at Earth, causing the planet to block the star light.
a
b
c
dAt what point on the velocity plot
will the planet block the star light ?
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Summary of Doppler Wobble MethodSummary of Doppler Wobble Method::Orbital PhysicsOrbital Physics
Kepler’s 3rd Law and Conservation of MomentumKepler’s 3rd Law and Conservation of Momentum
PP22 = 4 = 4 22/[G(M/[G(Mstarstar + M + Mplanetplanet)] a)] a33
P = orbital period a = orbital distance of planet from starP = orbital period a = orbital distance of planet from star
Simple Version of Kepler’s 3rd Law:Simple Version of Kepler’s 3rd Law:
PP22 = 4 = 4 22/GM/GMstarstar a a3 (3 (planet’s mass is negligible compared to star.)planet’s mass is negligible compared to star.)
Measure P from Doppler periodicity: Can solve for a.Measure P from Doppler periodicity: Can solve for a.
Circular Orbit: VCircular Orbit: Vplanetplanet = 2 = 2 a / P (Circumference/Time) a / P (Circumference/Time)
Momentum Conservation:Momentum Conservation:
MMstarstar V Vstarstar = M = MPlanetPlanet V Vplanetplanet
Mplanet = Mstar Vstar / VPlanet
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Doppler Wobble Method:Unknown Orbital Inclination
Tilt of Planet’s Orbital Plane: UnknownTilt of Planet’s Orbital Plane: Unknown• Edge-on Orbit: Full Doppler EffectEdge-on Orbit: Full Doppler Effect• Face-on Orbit: No Doppler EffectFace-on Orbit: No Doppler Effect• General Tilt Angle: True Wobble speed is General Tilt Angle: True Wobble speed is greater than Doppler indicatesgreater than Doppler indicates
True planet mass is GREATER than theTrue planet mass is GREATER than themass found by the Doppler method. (25% greater mass found by the Doppler method. (25% greater
on Avg.)on Avg.)
We measure M sin i
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Period = 4.2 days
Kepler’s 3rd Law: P2 = a3
Units: P in years, a in AU
Solve for a:a = 0.05 AU
Proximity: Temp = 1500 C
51 PegasiFirst Extrasolar Planet
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Detecting Extrasolar PlanetsDetecting Extrasolar Planets
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Kepler’s 3rd Law: P2 = a3
Momentum Conservation:Momentum Conservation:
MMSTARSTAR V VSTARSTAR = = MMplanetplanet V Vplanetplanet
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16 Cygni 16 Cygni BBMass = 1.7 M
JUP (Min)
Orbit PeriodOrbit Period
2.2 yr2.2 yr
Not SinusoidalNot Sinusoidal
VelocitVelocit
yy
WobbleWobble
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Velocity
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Orbit of Planet around 16 Cygni
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16 Cygni: Planet & Moon
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Life on Gas Giant Planets ?Life on Gas Giant Planets ?
FloatersFloaters
Earth-Like MoonEarth-Like Moon
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Eccentric Orbit ! of Planet around 16 Cygni