Download A105 Stars and Galaxies

A100 – Ch. 7
Extra-Solar
Planets
Begin Chapter 8 on Monday–
Terrestrial Planets
Hand in homework today
Quiz on Oncourse
Today’s APOD
The Sun Today
Today’s Topics
Solar systems around other stars
How do we find them
What are they like?
How are they similar to our solar system?
How do they differ
What kinds of stars have planets?
Worlds around other Suns
Evidence exists for
planets around other
nearby stars
The new planets are
not observed directly,
but rather by their
gravitational effects
on their parent star
These new planets are
a surprise - they are
huge planets very
close to their parent
stars
Note: All of these
images are artists’
conceptions
Our Solar
System
Gas Giants
Terrestrial
Planets
Plutoids
Ice Giants
Searching for Planets
More than 300 “extra-solar” planets
have been discovered
How are planets discovered?
Radial velocity
Transits
Gravitational lensing
Wobbles in stars’ positions
Discovering
Planets
from
Spectra
o The Doppler Shift!
o Absorption lines shift left or right if
stars move toward or away from us
o Planetary orbits cause stars’ radial
velocities to change
The Electromagnetic Spectrum
What is
Wavelength
???
Time
 Some phenomena are periodic
 They repeat in equal intervals of time
 The time between successive peaks is called wavelength
 Wavelength = Color
 Red light has longer wavelengths
 Blue light has shorter wavelengths
Where does light come from?
THERMAL
EMISSION
ATOMIC
EMISSION
Thermal radiators emit light at
all wavelengths
Atomic emission occurs only at
particular wavelengths
The Doppler Shift
Johan Christian Doppler
Doppler Pumpkin
Police Siren
The Doppler Effect
How does light tell us the speed of a
distant object?
How does light tell us the rotation
rate of an object?
Doppler Principles (Police Traffic
Radar Handbook)
The Doppler Shift of Sound Waves
What's Happening?
The Doppler Shift for Light
Astronomers us
the Doppler effect
to measure the
“radial” velocities
of astronomical
objects
Radial velocities
are motions toward
or away from us
Stationary
Moving Away
Away Faster
Moving Toward
Toward Faster
Measuring the Shift
Doppler shift tells us ONLY about the part of
an object’s motion toward or away from us
The amount of blue or red shift tells us an
object’s speed toward or away from us:
The Doppler Shift in YOUR Life
Periodic velocity changes due to orbiting planet
Velocity vs. Time
VERY high precision is needed
to measure these very small
velocity changes
Velocity (meters per second)
80
60
40
20
0
-20
-40
About 7 orbits in 30 days
P=4.2 days
-60
-80
0
10
20
30
Time (days)
Velocity of 51 Peg
40
A Planet around e Eridani
 A planet orbits the star e Eridani at a
radius of 3.2 A.U.
 e Eridani is similar to our Sun
 e Eridani is only 10.5 light years away
 The planet is similar to Jupiter
 The planet orbits e Eridani in 7 years
 e Eridani has at least one more planet
terrestrial
planets
The star u And has at least 3 planets
Planetary Transits
If the Earth lies in the same
plane as the orbit of a planet
we see a transit
•The planet passes across
the face of the star
•Some of the starlight is
blocked by planet and the
star appears dimmer
Seeing
planets
near stars
is hard
Looking for an Earthlike planet around a
nearby star is like standing on the East
Coast of the United States and looking
for a pinhead on the West Coast — with a
VERY bright grapefruit nearby.
Very large telescopes will help
This photo shows an image
of the faint star GQ Lupi
taken in the infrared. The
faint object to the right
of the star is a possible
planetary companion. It is
250 times fainter than the
star itself and it located
0.73 arcsecond west. At
the distance of GQ Lupi,
this corresponds to a
distance of roughly 100
astronomical units. The
planet probably has a mass
of about 2 x Jupiter.
Imaging
Planets?
Orbiting the
brown dwarf
~225 light
years away
Young, temp
near 1000K
Further from
its “sun” than
Pluto is from
ours
(brown dwarf is
blocked out)
Another
possible
planet
Location
of brown
dwarf

Possible planet
Properties of KNOWN
Extra-Solar Planets
SURPRISES!
All are gas giants like Jupiter and Saturn
Most are larger than Jupiter
Many orbit very close to their parent stars
Some are in systems with multiple planets
Many Known
Planets Are
Close to
Stars
(Masses are
given as Jupiter
masses)
The Sun
Hot Jupiters
Did these hot Jupiters
form further out, and
migrate inward as they
eject smaller bodies from
their planetary systems
BUT: Selection Effects
Close-in, massive planets are easier to
detect
Far-out planets and light-weight planets
are MUCH HARDER to detect
So far, we’ve only been able to detect
massive, close-in planets
Techniques, sensitivity are improving
Terrestrial planets soon!
Planet Mass
Distribution
The number of planets discovered decreases as
planet mass increases
There are few planets much more massive than
Jupiter
Most planets are <2 Jupiter masses
incomplete
How Far
Are Planets
from their
Stars?
Planets with semi-major axes > 3AU have
periods comparable to or longer than the length
of most Doppler surveys, so the distribution is
incomplete beyond that distance.
Period
Distribution
for Hot
Jupiters
A “pile-up” of planets with orbital periods
near 3 days – very close to central star
Why???
What are
the
planets’
orbits
like?
 What are the eccentricities of our sun’s planets?
 Planets within 0.1 AU are probably tidally circularized
 Beyond 0.1 AU, the distribution of eccentricities
appears essentially uniform between 0 and 0.8
 Very different from our solar system!
Looking for Another Earth
So far, we don’t have the right
instruments to detect Earth-like
planets
Requires large ground-based telescopes
or large, specially equipped space
telescopes
Stay tuned!
Dates
to
ASSIGNMENTS
Remember
this week
 Begin Chapter 8 – Terrestrial
Planets
 HAND IN HOMEWORK