Searching for Other Worlds:
John Bally1
1Center
for Astrophysics and Space Astronomy
Department of Astrophysical and Planetary
Sciences University of Colorado, Boulder
The Search for Exo-planets:
• The Context: The Age of Discovery
- Our generation is charting the Universe!
- Origns of the cosmos, stars, planets, and life
• How common are terrestrial (habitable) planets?
- Star and Planet Formation
- Astrobiology: The origins of life on Earth
In-situ searches in the Solar System
Remote-sensing biosignatures
• Methods of Discovery: Past, present, future (Saturday talk).
- Astrometry
- Radial velocity
- Transits
- gravitational lensing
- Direct detection, imaging, characterization
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Mission Development: From Concept to Flight to Science
- COROT, Kepler, SIM, TPF, Darwin , Starshade, Planet Imager, ….
The Age of Astronomical Discovery
• Access to all wavelengths of the spectrum
- Silicon technology
=> sensors at most wavelengths
- Large telescopes
• Powerful computers
• Access to space
- No atmosphere
a   X bl
=> Sharp images (Hubble Space Telescope)
=> Access to all wavelengths (Spitzer)
• Connections to Physics
- Scales: 1028 to 10-33 cm, 1017 to 10-43 sec
- 4 forces: gravity, electro-magnetism, weak, strong
- Matter (4%), Dark matter (24%), Dark energy (72%)
The Evolution of the Universe:
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Cosmology: Baryons = 4%
13.7 Gyr
Dark Matter = 26% (1 Gyr = 109 years)
Dark Energy = 70%
Cosmic Microwave Background:
The young Universe
400,000 years
Hot, ionized plasma 3,000 Kelvin
(1/2 temperature of Sun)
Smooth to 1:105
The Cosmic Dark Ages:
0.0004 – 0.6 Gyr
The First Stars: Massive
0.6
– 1 Gyr
Formation of Galaxies
> 1 Gyr
Solar System Formation:
9.1 Gyr
Star & Planet Formation today
Dark Energy: Expansion is accelerating!
Stars
Stars: The fundamental building blocks of the Universe
High mass: (8 - 100 times Mass of Sun)
Sources of light, chemical elements
Short lived: < 30 million years
Luminous: Thousand => million times Sun
Source of energy in interstellar medium
Explode as supernovae
Low Mass: (< 2 times Mass of Sun)
Long Lived: > Billion years
(Lock up mass for long time)
Planets: Abodes of life
Faint:
Introduction
• Star Formation:
The fundamental cosmic (baryonic) process
Determines cosmic fate of normal matter
Galaxy formation,
evolution, IMF
Star
Formation
Elements
(He => U)
Conditions for life
Planet formation
Clusters
Light, K.E. of ISM
black holes
(AGN, stellar)
M16
4 million
Year-old
Cluster
+
Ionized
Nebula
+
Surviving
cloud
M16
(HST)
Surviving
cloud
Star Formation
Shrink size by 107; increase density by x 1021 !
Where planets also form
• Giant Molecular Cloud Core
Raw material for star birth
• Gravitational Collapse & Fragmentation
Proto-stars, proto-binaries, proto-clusters
• Rotation & Magnetic Fields
Accretion disks, jets, & outflows
• Planets
Most may form in clusters!
C. Lada
Orion Nebula
Orion near-IR (Feigelson et al. 2005)
QuickTime™ and a
MPEG-4 Video decompressor
are needed to see this picture.
COUP X-rays (Feigelson et al. 2005)
QuickTime™ and a
MPEG-4 Video decompressor
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QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
Flux History, Typical 1 Mo Star
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Flux varies by 1000x
Peak flux approaches 107 G0.
Intense close encounters with core.
There is no `typical UV flux.’
Impulsive processing.
Planets in Formation?
d253-535 in M43
Smith et al. 05
Young Proto-planetary Disk
How common are close approaches?
HST 16
200 AU diameter
1” = 500 AU
HST 10
0.3 ly to O star
HST 17
Bally et al. 98
Anatomy of a planetary system
forming in an OB association
Sedimentation +
Photo-Evaporation
Self-irradiation
Gap opened at r = GM/c2
Viscous evolution +
Radial migration moves
dust into gap
Large dust:gas => planetesimals
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
The Search Extra-Solar Planets
Hard: Earth 1010 (10 billion) x fainter than Sun!
• Stellar Reflex Motion:
- Periodic Doppler variation
ground-based spectroscopy
- Periodic Position change
astrometry => space interferometry
• Transits (planet blocks light)
Kepler, TESS
• Gravitational Lensin
precission photometry
• Direct detection in images
coronagraphs, starshades
Direct imaging of exo-planets is Hard:
10 10
Sun
Earth
> 200 planets:
Most located
inside Earth’s orbit
Earth
Goeff Marcy
Paul Butler
radial velocity method
> 200 planets: Gas Giants like Jupiter
Orbit eccentricity
The Metallicity Effect:
The Search Extra-Solar Planets
Hard: Earth 1010 (10 billion) x fainter than Sun!
• Stellar Reflex Motion:
- Periodic Doppler variation
- Periodic Position change
• Transits (planet blocks light)
• Gravitational Lensing
• Direct detection in images
Quantitative estimate of reflex motion:
M*
mp
D*
Dp
CM
D* M*= Dp mp
Dp ~ r orbit
D* = (mp/M*) rorbit
V* = (mp/M*) Vorbit
Reflex Motion:
Planet
To Earth
Center of Mass
Parent Star
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Reflex Motion:
To Earth
Quantitative estimate of reflex motion:
MEarth = 6 x 1027 g
MJupiter = 1.7 x 1030 g
MSun
DEarth = 1.5 x 1013 cm (1AU)
DJupiter = 7.8 x 1013 cm
= 2 x 1033 g
D* = (mp/M*) rorbit
Earth @ 1AU
Jupiter@ 1AU
Jupiter @ 5.2 AU
4.5 x 107 cm
1.3 x 1010 cm
6.6 x 1010 cm
Searching for Other Worlds:
- Midterm #2 Next Friday
- Return mid-term / solutions posted
- HW#5 posted: Due Monday
searching for and characterizing exo-planets
Midterm #1 scores
The Search Extra-Solar Planets
Hard: Earth 1010 (10 billion) x fainter than Sun!
• Stellar Reflex Motion:
- Periodic Doppler variation
- Periodic Position change
• Transits (planet blocks light)
• Gravitational Lensing
• Direct detection in images
Quantitative estimate of reflex motion:
Orbital speed of planet:
Vp = (GM* / Dp)1/2
Orbital speed of star:
V* = Vp (D* / Dp)
V*
Earth @ 1AU
V*
Dp
Vp
D*
Jupiter@ 1AU
8.9 cm/s
25.4 m/s
Jupiter @ 5.2 AU 11.1 m/s
The Doppler Effect:
D n / n = D l / l = V*/ c
n  Frequency
ln  c
l  Wavelength
V*
Earth @ 1AU
8.9 cm/s
(v << c)
(speed of light)
Dl/l
3 x 10-10
25.4 m/s
8 x 10-8
Jupiter @ 5.2 AU 11.1 m/s
4 x 10-8
Jupiter@ 1AU
The Sun’s
Wobble
The first exo-planets:
Use radio timing of
Pulse-arival
- Doppler
-20
0
Time (days)
+20
Velocity variation of 51 Peg
(Doppler shift)
+50
0
-50
1
Goeff Marcy, Paul Butler
2
Time (days)
4
Gas-Giants Close-In: “Hot Jupiters”
Oribital Periods: 1 day => 1 year
D ~ 0.05 AU
to
> 1 AU
T ~ 1400 K
to
< 300 K
Giants => Composed of H, He (like Jupiter)
Evaporation of outer H in atmosphere
Earth-like planets, moons ?
Transits:
Transits:
Time (days)
Transit decreases light of star
Kepler: Transits
First planet
Discovered
Using the
Transit
method
Transit of HD209458b (HST)
UV absorption:
Escaping H and Na
Detected towards
HD209458
Recently, C and O
Have been detected
- escaping atmosphere!
Gravitational Lensing:
A cluster of galaxies `lensing’ more distant objects …
A star & its planets magnifying a
more distant star
Gravitational Lensing:
Magnification by star
-20
Magnification by
planet
Gravitational Lensing:
Star and planet magnifies
background starlight
0
-20
Time (days)
+20
Gravitational Lensing:
OGLE 2003-BLG0253
Gravitational Lensing:
Radio emission:
Jupiters
-20
0
Time (days)
+20
Exo-planet detection methods
Searching for Other Worlds:
- Midterm #2 Next Friday
- Return mid-term / solutions posted
- HW#5 posted: Due Monday
searching for and characterizing exo-planets
Methods for direct detection
and characterization of exo-planets :
Direct imaging with a coronagraph:
UV, visual, near IR
Mask light of star
control scattered light, diffraction
Large filled-aperture telescope
Interferometry
IR, radio
Link several telescope
pre-detection/post-detection
Ground vs. Space:
Ground:
- 10 – 100 meter vis/NIR
- Extreme adaptive optics to
correct turbulent images
- radio interferometry
(VLA, eVLA, SKA)
Space:
- 10 m + UV,VIS, NIR
- Interferometers
Future Projects for finding Planets:
Kepler: transits (2008+)
Atacama Large Millimeter Array (ALMA): 2010+
- mm interferometer:
direct detection of young gas giants
Next Generation Space Telescope
James Webb Space Telescope (JWST):
- direct imaging of forming gas giants?
Space Interferometry Mission (SIM):
- Astrometry (“defered”)
Terrestrial Planet Finder (TPF): (“defered”)
- Coronagraph
- IR interferometer
- Star Shade (Web Cash et al.)
Terrestrial Planet Imager (TPI): (?)
ALMA
(Atacama
Large
Millimeter
Array)
- Large next-generation space telescopes
(near-infrared & visual wavelength)
block parent star's light
Next Generation Space Telescope&
Finding planets around
other stars: (2010+)
-Space Interferometry
Mission (SIM)
measure stellar `wobble’
- Terrestrial Planet Finder
(TPF)
Direct detection of
Earth-sized planets
- Infrared `interferometer’
or
- visual `coronagraph’
Darwin
interferometer
Diffraction pattern of a circular aperture
Shaped telescopes: 0.3 < l < 3 mm
• Circular aperture diffracts light
in all directions.
- Light is scattered perpendicular to edges.
• Shaped aperture: Edges have limited
orientations
- Scatter light only into selected (unwanted)
directions
Diffraction patterns of shaped apertures
Earth as seen from 10 pc with various interferometers
Biosignatures: Spectra of various planets
IR (Stratosphere) vs. visible (Ground)