studying planets – challenges to overcome
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The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest. Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs. Studying Planets – Challenges to Overcome. - PowerPoint PPT PresentationTRANSCRIPT
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The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest. Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs.
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Studying Planets – Challenges to Overcome
Planets are faint- Much smaller than stars- emit only the star’s reflected light- high sensitivity of large telescopes is needed
Planets are close to their much brighter star- looking for a firefly in the bright beam of a light
house- high angular resolution is needed to separate the
planet from the star
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Planetary Systems: Questions
• Statistics of planetary systems
– How common are planetary systems?
– Are certain star types favored?
– What is the distribution of planetary systems in the Galaxy?
• Characterizing planetary systems
– What are the orbit radii?
– Are the orbits circular or eccentric?
– Are multiple-planet systems common?
• For multiple planet systems
– What is the typical mass distribution of planets in a system?
– What is the typical radius distribution?
– Are the orbits co-planar?
• Must have astrometry to answer this
– Are the planets stable?
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Planet Detection - Search Regimes for SIM
• Jupiter-mass planets
– Signature is ± 5 as at 1 kpc
– Very large number of available targets
• Intermediate mass range: 2 - 20 Earth masses
– Massive terrestrial planets
– Detectable to many 10s of pc
– SIM can survey a large number of stars for planets less massive than Jupiter
• Earth-like planets
– The most challenging science for SIM
– 1 Earth mass at 1 AU -> ± 0.3 as signature at 10 pc
– Earths detectable only out to a few pc
– Orbit parameters only for the closest systems
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To find life on other planets, first we need to find planets
“Naked Eye” planets
Telescope (1781)
Predicted by Newtonian Mechanics (1846)
Intensive telescope search (1930) - based on incorrect prediction!
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Astrometric Planet Detection: What do we derive from SIM measurements?
Astrometry can measure all of theorbital parameters of all planets.
Orbit parameter Planet PropertyMass Atmosphere?Semi-major axis TemperatureEccentricity Variation of tempOrbit Inclination Coplanar planets?Period
Sun’s reflex motion (Jupiter) ~500 µasSun’s motion from the Earth ~0.3 µas
1A.U. ~ 150,000,000 km
~80 A.U.
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A star will wobble because it orbits a common center of mass with its companion planets
There is more wobble when the companion planet is massive and close to the central star. Groundbased observers measure the Doppler shift. SIM will measure the positional wobble. Doppler shift or a well-determined stellar mass is necessary to determine the true orbit(s) and planet mass(es).
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Many “exoplanets” have been found by measuring the Doppler shift of starlight
First discovery of a planet around a “normal” star (1995)But these are large planets (1 Jupiter Mass = 318 Earth masses) AND many are very close to their central stars. The masses listed are lower limits.
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Where is the most interesting search volume?
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Search for Terrestrial Planets
• SIM adds direct information on masses and orbits for fuller characterization of planets from EarthsJupiters
• SIM planet search program has a strong “terrestrial” planets component balanced by a “broad” survey of 2000 stars of Uranus mass planets The nominal SIM deep planet search program occupies ~17% of SIM time, and can search ~250 stars @ 50 2D visits over 5 years. (or 125 stars @ 100 2D visits or 60 stars @ 200 visits…)– 50 2D visits => ~3 Mearth for 1AU orbit around the Sun
@ 10pc
• The exact observational program will be modified according to best available data at the time, e.g RV on individual stars and on the value of earth from the Kepler mission. (Just as TPF-C’s plan will be modified according to best available knowledge from, e.g. SIM)
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Search for Terrestrial Planets
• Blue, all terrestrial size planets. • Green/Yellow Habitable zones around 1&4 Lsun• Sample size 60~250 stars depending on earth in habitable zone (from COROT/Kepler)
SIM 5yr 200 visits60 stars
Habitable Zone1 L(sun) 4L(sun)Terrestrial sized
planets
(18 pc)
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Planet Mass I (Planet and Star Orbit)
• The planet and star orbit around their common center of mass.– The orbits are mirror images of each other, the planet orbit is ~100,000
times larger.– The mass of the planet is deduced by measuring the motion of the star.
(the mass of the star is measured by watching the planet
– MPlanet = Mstar*Rstar/RPlanet
• SIM measures Rplanet by using Kepler’s 3rd law, from the period of the planet and the mass of the star.
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Planet mass sensitivity vs distance
Best 240 targets are all within 30 pc
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False-alarm probability (FAP)
Choose detection threshold for 1% FAP
Gaussian noise has power at all frequencies: more frequencies searched → more false alarms
FAP at a given detection
threshold is the probability that a noise peak could
exceed the threshold
Monte Carlo of peak periodogram power for 100,000 realizations of Gaussian noise
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Finding Planets Indirectly
• Gravitational Effects on Parent Star
– Radial Velocity Changes
• Favors large planets in close to star
• Independent of distance
– Positional Wobble (Astrometry)
• Favors large planets far from star
• Angular displacement decreases with distance
• SIM’s technique
• Effect of Planet on Star’s Brightness
– Transits of edge-on systems
• Small fraction of a percent for a few hours (10-5 for an Earth)
– Gravitational Lensing
• Planetary companion of lensing star affects magnification of background star by few percent for a few hours
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Planetary Gravitational Lensing
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An Important Example of Using Astrometry• Deduce planets orbiting nearby stars
• Motion of our sun (1990-2020) due to all planets in our solar system as viewed from 10 parsec (a little more than 30 light years) away
Scales are ±0.001 arc sec= ± 1 milli arc second= ± 1000 micro arc sec~ ± 5 nano-radian
Motion of star’s optical center is a few thousand micro arc seconds (μas)
SIM could measure this motion with an accuracy of about 1 μas (~5 pico-radian)
(quite a bit thinner than the line plotted here)
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One Jupiter mass (1 MJ)
corresponds to 318 Earth masses.
Exoplanets Found by Doppler Shift of Starlight
SIM will eliminate orbit inclination ambiguity of radial velocity method and detect smaller planets in longer period orbits
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NEWSScientists discover first of a new class of extrasolar planets
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“The wobble effect”: our
Solar System as seen at 10 pc distance
• 1 tick mark = 200 µas• SIM accuracy = 1 µas (single meas.)• Sun-Jupiter wobble = 500 µas • Sun-Earth wobble = 0.3 µas
SIM Simulation:
detecting a planetary orbit with a series of 2-D
measurements
Principle of Astrometric Planet Detection
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1000 µas
1000µas
How Much Wobble?
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Astrometric Planet Detection:What do we derive from SIM measurements?
1A.U. ~ 150,000,000 km
~80 A.U.
Astrometry can measure all of theorbital parameters of all planets.
Orbit parameter Planet PropertyMass Atmosphere?Semimajor axis TemperatureEccentricity Variation of tempOrbit Inclination Coplanar planets?Period
Sun’s reflex motion (Jupiter) ~500 µasSun’s motion from the Earth ~0.3 µas
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What are the SIM Planet-Finding Plans?
• The SIM planet science program has 3 components.
• Searching ~200 nearby stars for terrestrial planets, in its Deep Search at (1 µas).
• Searching ~ 2000 stars in a Broad Survey at lower but still extremely high accuracy (4 µas) to study planetary systems throughout this part of the galaxy.
• Studying the birth of planetary systems around Young Stars so we can understand how planetary systems evolve.
– Do multiple Jupiters form and only a few or none survive during the birth of a star/planetary system?
– Is orbital migration caused primarily by Planet-Planet interaction or by Disk-planet interaction?
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Masses and Orbits of Planets SIM Can Detect
Planetary systems inducing low radial velocities (<10m/s) in their central star can be detected through the astrometric displacement of the parent star.
Systems accessible only with SIM.
SIM will be able to detect planets of a few Earth masses around nearby stars.
Ground based astrometric techniques.
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1
10
100
0.1 0.3 1.0 3.2 10.0 31.6100.0316.21,000.03,162.210,000.031,622.0
Planetary Mass (Earths) .
Number of Detected Planets
E JS
Masses of 104 known planets
UNV
Deep Search for Terrestrial Planets
• Ground-based radial velocity technique detects planets above a Saturn mass
• SIM will detect planets down to a few Earth masses and measure their masses
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But What is a Habitable Planet?
• Not too big • Not too small
• Not too hot or too cold
A good planet is:
SIM can find planets similar in mass to Earth, at the “right distance” from their parent stars
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Broad Survey of Planetary Systems
Out of 100 planetary systems discovered to-date, only one resembles our solar system
So:
• Is our solar system normal or unusual?
• Are planets more common around sun-like stars?
• What are the ‘architectures’ of other planetary systems
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Planets around Young Stars
• How do planetary systems evolve?
• Is the evolution conducive to the formation of Earth-like planets in stable orbits?
• Do multiple Jupiters form and only a few (or none) survive?
SIM will:• Search for Jupiter-mass planets
around young stars – Pick stars with a range of
ages• Measure the ages and
‘evolutionary state’ of young stars– Need precise distances and
companion orbits
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The “Close” Candidates
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HST Fine Guidance Sensors
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FGS-TRANS
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NICMOS Discoveries
GJ 54 AB
130 mas
mid-M
2 yr
Binary #2
430 mas
late-M
13 yr
Binary #3
130 mas
mid-M
2 yr
Binary #4
3 arcsec
early-L
… long
Binary #5
80 mas mid-L 2 yr
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MLR of VLMs
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Primary SIM Targets
• 250 A, F, G, K, M dwarfs within ~15 pc
– Doppler Recon. @ 1 m s-1
Jupiters & Saturns within 5 AU
– SIM: 30 obs. during 5 yr (1 as)
3 MEarth @ 0.5 - 1.5 AU
• 6 K-giant reference stars @ 0.5 - 1 kpc – Located within 1 deg of each target– Doppler vetting for binaries @ 25 m/s
5 5
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Radial Velocity Planet Searches
Detection Detection Limit:Limit:
~ 0.2 M~ 0.2 MJUP JUP @ 1 @ 1 AUAU
15 - 20 M15 - 20 Mearthearth
Gl 436Gl 436 55 Cnc d55 Cnc d AraAra
RV Limitations:RV Limitations: Only a < 0.1 AUOnly a < 0.1 AU M > 10 MM > 10 Mearthearth
( Butler et al. McArthur ( Butler et al. McArthur et al., Santos et al. )et al., Santos et al. )
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Can RV Detect Rocky Planets at 1 AU ?
Benchmark: 1 Earth Mass at 1 AU.
RV Amplitude: K = 0.09 m/s
RV Errors: = 1.0 m/s
S/N ~ K / ~ 0.1
RV Cannot Find
Earths Anywhere Near HZ
(Even with 1 m/s) Exception: M DwarfsException: M Dwarfs
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Nominal SIM Discovery Space
Unique SIM Domain:
3 - 30 MEARTH
Near Habitable Zones
•Unambiguous Mass
•Co-planarity of orbits in
multi-planet systems
• Orbital: a, P, e
SIMDomain
MASS(MEarth )
1 M1 Mearth earth @ 1 AU for d= 1 pc @ 1 AU for d= 1 pc ==> 3 ==> 3 microarcsecmicroarcsec
......
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Democritus:Pre-Socratic 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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PoorDetect-ability
Doppler Survey of 1330 Nearby Sun-like Stars
Extrapolation: 6% of stars
have giant planets beyond 3 AU
Armitage, Livio, Lubow, Pringle Armitage, Livio, Lubow, Pringle
et al. 2002et al. 2002
Trilling, Benz, Lunine 2002Trilling, Benz, Lunine 2002
Model:Inward Migration:Planets left behindas disk vanishes
Rise?Rise?
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Planet – Metallicity Correlation
Fischer & Valenti 2005
Abundance
Analysis of all 1000
stars:
SpectralSpectral
SynthesisSynthesis
Valenti & Fischer 2005
1.61.6
PPplanetplanet ~ ~ ((NNFeFe
/ N/ NHH))
Fe/HFe/H
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Models of Protoplanetary Disks of Gas & Dust
TheoreticalPlanet-Formation:
Dust Growth pebbles/rocks Grav. Runaway Gas Accretion
Migration & Interactions
Formation of Planetary Systems:
ObservationsObservations mm-wave dust emission IR Excess/Spectra & SEDs HST Imaging
MDISK = 10-100 MJUP
Disk Lifetime ~ 3 Myr
The Solar System Paradigm
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Multi-Planet Interactions
Levison, Lissauer, Duncan1998
100 Planet “Embryos” (~MEarth)
Scatter, Collide, Stick, Accrete Gas
Chaos
After 21.5 Myr
After 30 Myr
Lone Close-in,Lone Close-in,
Jupiter inJupiter in
Eccentric Orbit.Eccentric Orbit.
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Levison, Lissauer, Duncan 1998
Size Planet mass (in M earth ) above each
planet.
Peri - Apo of
orbit
AUAU
-- -- --Rocky Planets willRocky Planets will
Outnumber jupiters.Outnumber jupiters.
Monte Carlo Examples of Planetary Systems
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Low-Precision Planet Search
• 400 AFGKM stars at 10-30 pc– SIM precision: 4 as– Use “SIM GRID” (not nearby Ref Stars)– Doppler Recon. at 1 m/s
==> Jupiters and Saturns within 5 AU
4 as @ 30 pc reveals:
30 Mearth at 1 AU
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Error bars are 1 uas
SIM: 3 Earth-Mass Planets
d = 5pc
precision 1 microarcsec
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61 Cygni A
Exp. Error• Photons• Angle
sep.• Planet
jitter
Failure Prob.
1o
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Typical M Dwarf Companion
Eliminate Companions:
25 m/s RV Precision
RV Vetting of Reference Stars
Planetsaround K giantsget through
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61 Cygni A: Proper Motion
Nuisance Stars
Fringe Contamination
if within 2 arcsec
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SIM Synergy with TPF
TPF inner working Angle
• SIM ~250 closest stars: Identify targets for
TPF-c Definite targets: SIM finds
rocky planets - in the habitable zone
Potential targets: 2- SIM
earths - enrich TPF target lists
Avoid targets: SIM finds a giant planet in the habitable zone
Catch planets when they are 4 /d = 65 mas from star.
TPF Timing:
Inner Working DistanceInner Working Distance
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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
QuickTime™ and aTIFF (Uncompressed) decompressor
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Gliese 436: Velocity vs. Phase
Msini = 21 MEarth
M ~ 21 MEarth
a = 0.03 AU
K ~ Mpl / a1/2
3 Mearth at1 AU
K = 10 cm/sAt 1 AU,RV can detect20 MEarth
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• What fraction of young stars have gas-giant planets?– Only SIM astrometry can find planets around young stars since active
stellar atmospheres and rapid rotation preclude radial velocity or transit searches
• Do gas-giant planets form at the “water-condensation” line? – SIM will survey ~200 stars to a level adequate to find Jovian or smaller
planets on orbits <1 AU to >5 AU around stars from 25-150 pc– 4 as precision NAngle (50-150 pc) and 12 as precision WAngle (25-
50 pc)• Does the incidence, distribution, and orbital parameters of planets change
with age and protostellar disk mass? – Study of clusters with ages spanning 1-100 Myr to test orbital migration
theories– Correlate with Spitzer results on disks (4-24 m)
• Where, when, and how do terrestrial planets form ?– Understand the formation and orbital migration mechanisms of the
giant planets• No other technique before and possibly including TPF (RV, AO imaging,
IR interferometry) can credibly claim to find planets down to Saturn-Jupiter mass within 1-10 AU of parent stars at 25-150 pc
How Do Planetary Systems Form and Evolve?
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JWST and AO Imaging Will Find Young Jupiters in Large Orbits (>30 AU)
• ESO and other telescopes beginning to identify possible gas giants at 10s-100s of AU
• At 5 m NIRCAM on JWST will be powerful tool for finding distant planets outside of 50 AU (3/D=0.575"=30~100 AU at 50-150 pc)
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Possible Detections for 1 M primary with 500 m/s• 1 M companion, 4 AU: vrad ~ 11 km/s, P ~ 11 yrs (SB2)•50 MJ companion, 1 AU: vrad ~ 2 km/s, P ~ 1.5 yrs (few years)•50 MJ companion, 0.1 AU: vrad ~ 6 km/s, P ~ 15 days (few days)•10 MJ companion, 0.3 AU: vrad ~ 600 m/s, P ~ 50 days (few months)
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Adaptive Optics Results
• AO Observations of Northern targets nearly complete from Palomar (Tanner, Dumas, Hillenbrand, Beichman)– K=9 mag at 1-2″– 14 out of 14 Pleiades targets
• 5 targets have 8 visual companions (>2.5″)
– 16 out of 19 Tau Aur targets • 11 have 20 visual
companions (>2.5″)• 80 hours scheduled for March 2004
to observe 15 stars in Sco Cen and Upper Sco with VLT AO (Dumas et al.)
• Speckle observations of Northern targets planned from Keck (Ghez)– In 2000, identified 3 potential
targets with companions <1″• Keck-Interferometer suggests V830
Tau is multiple
BP Tau
Hii1309 (Pleiades)
3.1"