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Studying Planets – Challenges to Overcome PowerPoint Presentation
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Studying Planets – Challenges to Overcome

Studying Planets – Challenges to Overcome

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Studying Planets – Challenges to Overcome

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  1. 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.

  2. 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

  3. 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?

  4. 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

  5. To find life on other planets, first we need to find planets Intensive telescope search (1930) - based on incorrect prediction! Predicted by Newtonian Mechanics (1846) Telescope (1781) “Naked Eye” planets

  6. Astrometric Planet Detection: What do we derive from SIM measurements? 1A.U. ~ 150,000,000 km ~80 A.U. Astrometry can measure all of the orbital parameters of all planets. Orbit parameter Planet Property Mass Atmosphere? Semi-major axis Temperature Eccentricity Variation of temp Orbit Inclination Coplanar planets? Period Sun’s reflex motion (Jupiter) ~500 µas Sun’s motion from the Earth ~0.3 µas

  7. 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).

  8. 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.

  9. Where is the most interesting search volume?

  10. Search for Terrestrial Planets • SIM adds direct information on masses and orbits for fuller characterization of planets from EarthsJupiters • 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 hearth from the Kepler mission. (Just as TPF-C’s plan will be modified according to best available knowledge from, e.g. SIM)

  11. Search for Terrestrial Planets Habitable Zone 1 L(sun) 4L(sun) Terrestrial sized planets SIM 5yr 200 visits 60 stars • Blue, all terrestrial size planets. • Green/Yellow Habitable zones around 1&4 Lsun • Sample size 60~250 stars depending on hearth in habitable zone (from COROT/Kepler) (18 pc)

  12. 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.

  13. Planet mass sensitivity vs distance Best 240 targets are all within 30 pc

  14. False-alarm probability (FAP) 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 Choose detection threshold for 1% FAP Gaussian noise has power at all frequencies: more frequencies searched → more false alarms

  15. 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

  16. Planetary Gravitational Lensing

  17. 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)

  18. Exoplanets Found by Doppler Shift of Starlight • One Jupiter mass (1 MJ) corresponds to 318 Earth masses. SIM will eliminate orbit inclination ambiguity of radial velocity method and detect smaller planets in longer period orbits

  19. NEWS Scientists discover first of a new class of extrasolar planets

  20. Principle of Astrometric Planet Detection SIM Simulation: detecting a planetary orbit with a series of 2-D measurements “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 1000 µas How Much Wobble? 1000 µas

  21. Astrometric Planet Detection:What do we derive from SIM measurements? Astrometry can measure all of the orbital parameters of all planets. Orbit parameter Planet Property Mass Atmosphere? Semimajor axis Temperature Eccentricity Variation of temp Orbit Inclination Coplanar planets? Period 1A.U. ~ 150,000,000 km Sun’s reflex motion (Jupiter) ~500 µas Sun’s motion from the Earth ~0.3 µas ~80 A.U.

  22. 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?

  23. Masses and Orbits of Planets SIM Can Detect Ground based astrometric techniques. SIM will be able to detect planets of a few Earth masses around nearby stars. Systems accessible only with SIM. Planetary systems inducing low radial velocities (<10m/s) in their central star can be detected through the astrometric displacement of the parent star.

  24. Deep Search for Terrestrial Planets Masses of 104 known 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 V E U N S J

  25. But What is a Habitable Planet? • Not toobig • Not toosmall • Not toohotor toocold A good planet is: SIM can find planets similar in mass to Earth, at the “right distance” from their parent stars

  26. 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

  27. 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

  28. The “Close” Candidates

  29. HST Fine Guidance Sensors


  31. NICMOS Discoveries

  32. MLR of VLMs

  33. 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 mas) 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 s

  34. Radial Velocity Planet Searches 15 - 20 Mearth • Gl 436 • 55 Cnc d • m Ara RV Limitations: • Only a < 0.1 AU • M > 10 Mearth ( Butler et al. McArthur et al., Santos et al. ) Detection Limit: ~ 0.2 MJUP @ 1 AU

  35. Can RV Detect Rocky Planets at 1 AU ? Benchmark: 1 Earth Mass at 1 AU. RV Amplitude: K = 0.09 m/s RV Errors: s = 1.0 m/s S/N ~ K / s ~ 0.1 RV Cannot Find Earths Anywhere Near HZ (Even with 1 m/s) Exception: M Dwarfs

  36. Nominal SIM Discovery Space Unique SIM Domain: 3 - 30 MEARTH Near Habitable Zones 3000 300 MASS (MEarth ) 30 3 . . SIM Domain . • Unambiguous Mass • Co-planarity of orbits in • multi-planet systems • Orbital: a, P, e 1 Mearth @ 1 AU for d= 1 pc ==> 3 microarcsec

  37. Democritus:Pre-SocraticGreekphilosopher(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.”

  38. Doppler Survey of 1330 Nearby Sun-like Stars Extrapolation: 6% of stars have giant planets beyond 3 AU Poor Detect- ability Rise? Model: Inward Migration: Planets left behind as disk vanishes Armitage, Livio, Lubow, Pringle et al. 2002 Trilling, Benz, Lunine 2002

  39. Planet – Metallicity Correlation Abundance Analysis of all 1000 stars: Spectral Synthesis 1.6 Pplanet ~ (NFe/ NH) Fe/H Fischer & Valenti 2005 Valenti & Fischer 2005

  40. Formation of Planetary Systems: The Solar System Paradigm Models of Protoplanetary Disks of Gas & Dust Observations • mm-wave dust emission • IR Excess/Spectra & SEDs • HST Imaging •  MDISK = 10-100 MJUP • Disk Lifetime ~ 3 Myr Theoretical Planet-Formation: • Dust Growth  pebbles/rocks • Grav. Runaway • Gas Accretion Migration & Interactions

  41. Multi-Planet Interactions • 100 Planet “Embryos” (~MEarth) • Scatter, Collide, Stick, • Accrete Gas Levison, Lissauer, Duncan1998 After 21.5 Myr Chaos After 30 Myr Lone Close-in, Jupiter in Eccentric Orbit.

  42. Levison, Lissauer, Duncan 1998 Monte Carlo Examples of Planetary Systems • Size  Planet mass (in M earth ) above each planet. Peri - Apo of orbit - - - Rocky Planets will Outnumber jupiters. AU

  43. Low-Precision Planet Search • 400 AFGKM stars at 10-30 pc • SIM precision: 4 mas • Use “SIM GRID” (not nearby Ref Stars) • Doppler Recon. at 1 m/s ==> Jupiters and Saturns within 5 AU 4 mas @ 30 pc reveals: 30 Mearth at 1 AU

  44. SIM: 3 Earth-Mass Planets precision 1 microarcsec d = 5pc Error bars are 1 uas

  45. 61 Cygni A Exp. Error • Photons • Angle sep. • Planet jitter Failure Prob. 1o

  46. RV Vetting of Reference Stars Typical M Dwarf Companion Eliminate Companions: 25 m/s RV Precision Planets around K giants get through

  47. Nuisance StarsFringe Contaminationif within 2 arcsec 61 Cygni A: Proper Motion

  48. 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-s SIM earths - enrich TPF target lists Avoid targets: SIM finds a giant planet in the habitable zone TPF Timing: Catch planets when they are 4 l/d = 65 mas from star. Inner Working Distance

  49. Epicurus (341-270 B.C.) Greek philosopher in Athens where he opened a school of philosophy “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…”