Published on November 15, 2007
JOHANNES KEPLER: JOHANNES KEPLER A guy who’s thought a lot about planets ( By permission Sternwarte Kremsmünster) Kepler MissionA SEARCH FOR HABITABLE PLANETS: Kepler Mission A SEARCH FOR HABITABLE PLANETS David Koch NASA Ames Research Center Ames Internship Program 27 October 2004 OVERVIEW: 3 OVERVIEW What makes for a Habitable Planet Different Methods for Finding Planets Planets Discovered to date Transit Photometry Kepler Mission Concept Expected Results WHAT DOES HABITABLE MEAN TO YOU?: 4 WHAT DOES HABITABLE MEAN TO YOU? WHAT DOES HABITABLE MEAN TO YOU?: 5 WHAT DOES HABITABLE MEAN TO YOU? Right temperature Air Liquid water Light Radiation shield Asteroid protection “This land is your land, and this land is my land From the California, to the New York island From the Redwood Forest, to the Gulf Stream waters -- This land was made for you and me. “As I went walking that ribbon of highway, I saw above me that endless skyway, I saw below me that golden valley -- This land was made for you and me. “I roamed and rambled and I followed my footsteps To the sparkling sands of her diamond deserts All around me a voice was sounding -- This land was made for you and me. “When the sun comes shining and I was strolling And the wheat fields waving and the dust clouds rolling The voice was chanting as the fog was lifting This land was made for you and me.“ Words and music by Woody Guthrie (1940) THINGS THAT AFFECT TEMPERATURE: 6 THINGS THAT AFFECT TEMPERATURE Want temperature so you can have liquid water on the surface of the planet Temperature of star Stellar mass determines temperature and size type mass temp °K radius O5 60 42,000 12 B5 5.9 15,200 3.9 A0 2.9 9,790 2.4 F0 1.6 7,300 1.5 G2 (Sun) 1.0 5,790 1.0 K0 0.79 5,150 0.85 M2 0.40 3,520 0.50 STELLAR SIZES AND MASSES: 7 STELLAR SIZES AND MASSES The mass (in solar masses) and radius (in AU) of dwarf stars, also known as main-sequence stars or luminosity class V, are shown in black. The Sun has a radius of 0.00467 AU and a mass of 1 solar mass. Giant stars, luminosity class III, of the same spectral type are shown in red. THINGS THAT AFFECT TEMPERATURE: 8 THINGS THAT AFFECT TEMPERATURE 2. Distance from the star 3. Shape of planet’s orbit circular or elliptical 4. Planet’s atmosphere Greenhouse gases These define the Habitable Zone (HZ) for a star THE HABITABLE ZONE FOR VARIOUS STELLAR TYPES: 9 THE HABITABLE ZONE FOR VARIOUS STELLAR TYPES The Habitable Zone (HZ) in green is the distance from a star where liquid water is expected to exist on the planets surface. (Kasting, Whitmire and Reynolds, 1993) WHAT IS IMPORTANT ABOUT AN ATMOSPHERE?: 10 WHAT IS IMPORTANT ABOUT AN ATMOSPHERE? Composition (Earth) free oxygen (about 23%) mostly inert (about 75% nitrogen) very little toxic gases Composition affects temperature Minimize day-night extremes Greenhouse gases (water, CO2) hold in the heat Acts as a shield Cosmic rays (high energy gamma-rays, protons, electrons) Solar wind and solar flares (charged particles) UV - ultraviolet Micrometeoroids (put a hole through Space Shuttle window) Transports water Rain PLANET SIZE: 11 PLANET SIZE Planets form by accretion from a disk of gas and dust Too small (about <0.5 MÅ): Can’t hold onto a life sustaining atmosphere (Mercury, Mars) surface gravity g=0.8 G Too big (about >10 MÅ): Can hold onto the very abundant light gases (H2 and He) and turn into a gas giant (Jupiter, Saturn, Uranus, Neptune) surface gravity g=2.2 G (Surface gravity proportional to radius) Copyright Lynnette Cook Planet size affects habitability PLANETS IN OUR SOLAR SYSTEM: 12 PLANETS IN OUR SOLAR SYSTEM Terrestrials Gas giants Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto mass 0.055 0.82 1.00 0.11 318 95 14 17 .0002 radius 0.38 0.95 1.00 0.53 11.2 9.4 4.0 3.9 0.18 area 0.15 0.90 1.00 0.28 126 89 16 15 0.03 volume 0.06 0.85 1.00 0.15 1408 844 64 59 0.006 density 0.98 0.95 1.00 0.71 0.24 0.12 0.24 0.32 0.20 (all values are relative to Earth) BOTTOM LINE: 13 BOTTOM LINE Key features for habitable planets Habitable zone (temperature) Planet size (mass) Reference: Rare Earth, Ward and Brownlee, Copernicus (Springer-Verlag) ISBN 0-387-98701 DETECTING EXTRA-SOLAR PLANTS: 14 DETECTING EXTRA-SOLAR PLANTS Meaning of extra-solar Planets outside our solar system Or Planets orbiting other stars TECHNIQUES FOR FINDING EXTRASOLAR PLANETS: 15 TECHNIQUES FOR FINDING EXTRASOLAR PLANETS Method Yield Mass Limit Status Pulsar Timing m/M ; t Lunar Successful (3) Radial Velocity m sini ; t Uranus Successful (~120) Astrometry m ; t ; Ds ; a Ground: Telescope Jupiter Ongoing Ground: Interferometer sub-Jupiter In development Space: Interferometer Uranus Being studied Transit Photometry A ; t ; sini=1 Ground sub-Jupiter HD209458, OGLE TR-56 Space Venus Planned Kepler Reflection Photometry: albedo*A ; t Space Saturn Planned Kepler Microlensing: f(m,M,r,Ds,DL ) Ground sub-Uranus On-going Direct Imaging albedo*A ; t ; Ds ; a ; M Ground Saturn Being studied Space Earth Being studied (Source: J. Lissauer) SEARCH RESULTS: 16 SEARCH RESULTS The first 50 known extrasolar planets are shown along with the planets in our solar system. The limit for planet detection using Doppler spectroscopy is shown. The range of habitable planets (0.5 to 10 MÅ) in the HZ is shown in green. WE NEED A DIFFERENT APPROACH: 17 WE NEED A DIFFERENT APPROACH Radial velocity (Doppler spectroscopy) method unable to detect Earth-size planets Earth-like planets are about 300 times less massive and about 100 times smaller in area than Jupiter Need a different approach that can detect smaller planets No method exists for detecting habitable planets from ground-based observatories The Kepler Mission uses photometry to detect transits and can detect Earth-size planets from space The Kepler Mission is optimized to detect habitable planets in the habitable zone of solar-like stars USING PHOTOMETRY TO DETECT PLANETS: 18 USING PHOTOMETRY TO DETECT PLANETS Transits Planet crosses line of sight between observer and star and blocks a small amount of light from the star Different from occultation or eclipse Occult means to cover over or to hide Photometry Method of measuring the amount of light A light meter on a camera is a simple photometer USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS: 19 USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS The relative change in brightness (DL/L) is equal to the relative areas (Aplanet/Astar) To measure 0.01% must get above the Earth’s atmosphere Method is robust but you must be patience: Require at least 3 transits preferably 4 with same brightness change, duration and temporal separation Jupiter: 1% area of the Sun (1/100) Earth or Venus 0.01% area of the Sun (1/10,000) GEOMETRY FOR TRANSIT PROBABILITY: 20 GEOMETRY FOR TRANSIT PROBABILITY Not all planetary orbits are aligned along our line of sight to a star Diameter of Sun d* is about 0.01 AU. Diameter of Earth orbit D is 2 AU Random probability of detecting a Sun-Earth analog is about 0.5% So one needs to look at thousands of stars IF all have an Earth (Ref: Koch & Borucki, Circumstellar Habitable Zones, p229-237, R. Doyle ed., Travis House, 1996) Kepler MISSION CONCEPT: 21 Kepler MISSION CONCEPT Kepler Mission is optimized for finding habitable planets ( 0.5 to 10 MÅ ) in the HZ ( near 1 AU ) of solar-like stars Continuously and simultaneously monitor 100,000 main-sequence stars Use a one-meter Schmidt telescope: FOV >100 deg2 with an array of 42 CCD Photometric precision: Noise < 20 ppm in 6.5 hours V = 12 solar-like star => 4s detection for Earth-size transit Mission: Heliocentric orbit for continuous viewing > 4 year duration Kepler PHOTOMETER: 22 Kepler PHOTOMETER Photometer = CCDs + (Telescope = optics + metering structure) Kepler will be 9th largest Schmidt ever built Proto Type CCDs: 23 Proto Type CCDs Views of a prototype module composed of two CCDs mounted to a common carrier Each CCD is 2200 columns by 1024 rows, thinned, back-illuminated, anti-reflection coated, 4-phase devices manufactured by e2v. Each CCD has two outputs with the serial channel on the long edge. The pixels are 27 m square, corresponding to 3.98 arcsec on the sky. Kepler SPACECRAFT: 24 Kepler SPACECRAFT (Colors are only meant to represent different sub-systems) EARTH-TRAILING HELIOCENTRIC ORBIT: 25 EARTH-TRAILING HELIOCENTRIC ORBIT Delta II 2925-10L FIELD OF VIEW IN CYGNUS: 26 FIELD OF VIEW IN CYGNUS A region of the extended solar neighborhood in the Cygnus-Lyra regions along the Orion arm of our galaxy has been chosen. DETECTABLE PLANETS FOR V=12 STAR: 27 DETECTABLE PLANETS FOR V=12 STAR The detectable planet size is shown for a nearly central transit as a function of the stellar size and orbit. For a solar-like star (G2V) and a 1 AU orbit a planet somewhat smaller than Earth can be detected. Detections are based on a total SNR >8s and >3 transits in 4 years. EXPECTED RESULTS: 28 The minimum detectable planet size versus planetary orbital period for a 12th magnitude solar-like star (G2), a CDPP of 20 ppm and >4 grazing transits. (Ref: Koch et al, , Overview and Status of the Kepler Mission, SPIE Conf 5487,p1491-1500 Optical, Infrared, and Millimeter Space Telescopes, J. Mather ed., Glasgow, Scotland, 2004) EXPECTED RESULTS EXPECTED RESULTS: 29 EXPECTED RESULTS Hypothesis: all dwarf stars have planets and monitor 100,000 dwarf stars for 4 years Transits of terrestrial planets: About 50 planets if most have R~1.0 RÅ (M~1.0 MÅ ) About 185 planets if most have R~1.3 RÅ (M~2.2 MÅ ) About 640 planets if most have R ~2.2 RÅ (M~10 MÅ ) About 70 cases (12%) of 2 or more planets per system Transits of thousands of terrestrial planets: If most have orbits much less than 1 AU Modulation of reflected light of giant inner planets: About 870 planets with periods ≤1 week, 35 with transits Albedos for 100 giants planets also seen in transit Transits of giant planets: About 135 inner-orbit planet detections Densities for about 35 giants planets from radial velocity data About 30 outer-orbit planet detections Results expected will most likely be a mix of the above SCHEDULE AND RESULTS: SCHEDULE AND RESULTS 30 SCIENCE TEAM: 31 SCIENCE TEAM William Borucki, Principal Investigator, NASA Ames Research Center David Koch, Deputy Principal Investigator, NASA Ames Research Center Co-Investigator’s Working Group G. Basri UC-Berkeley T. Brown HAO/NCAR W. Cochran McDonald Obs./U. Texas E. DeVore SETI Institute E. Dunham Lowell Observatory J. Geary SAO R. Gilliland STScI A. Gould Lawrence Hall of Sci/UC-B J. Jenkins SETI Institute Y. Kondo NASA/GSFC D. Latham SAO J. Lissauer NASA/ARC Science Working Group A. Boss Carnegie Institute of Washington D. Brownlee University of Washington J. Caldwell York University A. Dupree SAO S. Howell Planetary Science Institute G. Marcy UC-Berkeley D. Morrison NASA/ARC T. Owen University of Hawaii H. Reitsema Ball Aerospace D. Sasselov SAO J. Tarter SETI Institute MANAGEMENT TEAM Chet Sasaki, Project Manager at Jet Propulsion Lab Larry Webster, Deputy Project Manager at NASA Ames Research Center Len Andreozzi, Program Manager Ball Aerospace, Boulder, CO SUMMARY: SUMMARY The Kepler Mission will: Observe more than 100,000 dwarf stars continuously for 4 to 6+ years with a precision capable of detecting Earth’s in the HZ The Kepler Mission can discover: Planet sizes from that of Mars to greater than Jupiter Orbital periods from days up to two years About 600 terrestrial planetary systems if most have 1 AU orbits About 1000 inner-orbit giant planets based on already known frequency Can expect 100’s to 1000’s of ??? size planets depending on frequency ??? and orbit ??? A NULL result would also be very significant ! ! ! Results begin 3 months after launch in Oct. 2007 and continue for 4 to 6+ years 32 New Yorker Cartoon: New Yorker Cartoon “Well, this mission answers at least one big question: Are there other planets like ours in the universe?” Drawing by H. Martin; © 1991 The New Yorker Magazine, Inc. 33 Backups: 34 Backups THINGS THAT AFFECT TEMPERATURE: 35 THINGS THAT AFFECT TEMPERATURE 2. Distance from the star 3. Shape of planet’s orbit circular or elliptical 4. Planet’s atmosphere Greenhouse gases These define the Habitable Zone (HZ) for a star 1. Type of star (mass, temperature and size) MOTIVATION: MOTIVATION • Fundamental human question: Are we alone? (public) • Deeper scientific question: What is the frequency of Earth-size planets? (theory) • Future space missions: How to build or not to build TPF? (NASA managers) • Many others… • Kepler Mission goals are … 36 Kepler GOALS: Kepler GOALS Explore the structure and diversity of planetary systems. This is achieved by observing a large sample of dwarf stars to: 1. Determine the frequency of terrestrial and larger planets in or near the habitable zone of a wide variety of spectral types of stars; 2. Determine the distributions of size and semi-major axis of these planets; 3. Estimate the frequency and orbital distribution of planets in multiple-star systems; 4. Determine the distributions of semi-major axis, albedo, size, mass and density of short-period giant planets; 5. Identify additional members of each photometrically discovered planetary system using complementary techniques; and 6. Determine the properties of those stars that harbor planetary systems. 37 ASTROPHYSICAL VALUE OF PHOTOMETRY WITH KEPLER MISSION: 38 ASTROPHYSICAL VALUE OF PHOTOMETRY WITH KEPLER MISSION Stellar Physics Value Stellar rotation rates Extensive data set p-mode oscillations Window to stellar interior: Mass, age, He abundance Characteristics of solar-type stars Define: What is a "normal" star? Frequency of Maunder minimums Earth climatic implications, paleoclimatology Stellar activity Star spot cycles, white light flaring Astrophysics Value Cataclysmic Variables Pre-outburst activity, mass transfer Eclipsing binaries Frequency of high-mass-ratio systems Active Galactic Nuclei variability "Engine" size in BL Lac, quasars, blazars (Ref: NASA CP-10148, "Astrophysical Science with a Spaceborne Photometric Telescope") COMPARISON: 39 COMPARISON My apologies if any number is incorrect or out-of-date EXTENDED SOLAR NEIGHBORHOOD: 40 EXTENDED SOLAR NEIGHBORHOOD The stars sampled are similar to the immediate solar neighborhood. Young stellar clusters, ionized HII regions and the neutral hydrogen, HI, distribution define the arms of the Galaxy. The view is from the north galactic pole looking down onto the galactic plane SEARCH SPACE SENSITIVITY: 41 SEARCH SPACE SENSITIVITY The limit of Kepler for planet detection of planets around a solar-like star is shown by the yellow region Ground based photometry is limited by the Earth’s atmosphere The range of habitable planets (0.5 to 10 MÅ) in the HZ is shown in green. BRIEF HISTORY: BRIEF HISTORY • 1952 Struve suggests advantages of photometric detection vs. radial velocity • 1974 Rosenblatt paper suggesting looking for planetary transits • 1984 Borucki and Summers paper on transit detection • 1992 Present concept at Discovery workshop, San Juan Capistrano • 1994 First Discovery proposal as FRESIP (cost not believable) • 1996 Second Discovery proposal as Kepler (technically weak) Conducted CCD testing for next go-round • 1998 Third Discovery proposal (believed single CCD test, but questioned system performance) Performed Tech Demo of end-to-end system with transit detection • 2000 Fourth Discovery proposal (one of three selected for study phase) • 2001 Dec 21 selected as Discovery mission #10 (DAWN selected as #9) 42 AFTER SELECTION: AFTER SELECTION Delayed phase B startup by one year, but… Told by Ed Weiler to maintain schedule for CCDs and optics Told to select either GSFC or JPL to manage the development After a lot of … , JPL was named as the management center Kick-off with new team member (JPL) in June 2002 Replanned/recosted program with one-year slip to Oct 2007 launch System Requirements Review October 2003 Preliminary Design Review October 2003 43 ORGANIZATION CHART: ORGANIZATION CHART We are really organized or Really, we are organized 44 KEY PARAMETERS FOR PHOTOMETRIC DETECTION OF EXTRASOLAR PLANETS: 45 KEY PARAMETERS FOR PHOTOMETRIC DETECTION OF EXTRASOLAR PLANETS Duration of a transit: tc =13 a1/2 M1/4 hrs ~ 13 a1/2 hrs (a in AU) when crossing the center of the star Relative brightness change caused by a transit: DL/L = Ap/A*, area Earth/area Sun = 84 ppm Probability of seeing a transit: p = radius of star / radius of orbit = 0.5% r*/a (r* solar radii, a in AU) Robust but must be patience: Require at least 3 transits preferably 4 with same brightness change, duration and temporal separation CONTINUOUSLY VIEWABLE HIGH DENSITY STAR FIELD: CONTINUOUSLY VIEWABLE HIGH DENSITY STAR FIELD One region of high star field density far (>55°) from the ecliptic plane where the galactic plane is continuously viewable is centered at RA=19h22m Dec=44°30’. The 55° ecliptic plane avoidance limit is defined by the sunshade size for a large aperture wide field of view telescope in space. 46 NUMBER AND DISTANCE OF DWARF STARS FOR WHICH VARIOUS PLANETS CAN BE DETECTED: 47 NUMBER AND DISTANCE OF DWARF STARS FOR WHICH VARIOUS PLANETS CAN BE DETECTED Based on planets in a 1-yr orbit, detection SNR > 8s, transits lasting 80% of central transit duration and monitoring of 100,000 dwarf stars as faint as V=14 for 4 years. Planets in shorter period orbits have a greater detectability. PROGRAM PHASES: PROGRAM PHASES Phase A Concept Study (Aug ‘01) (Mostly done in 4 proposals) Phase B Engineering solution for all subsystems, cost to complete, Start long lead procurements Lock up requirements, System Requirements Rev (SRR) Oct ‘03 Ends with Preliminary Design Review (PDR) Oct ‘04 and Confirmation Review (CR) Dec ‘04 Phase C Detailed design and manufacturing drawings Ends with Final Design Review (CDR) Oct ‘05 Phase D Fabricate, assemble, test, launch (Oct ‘07) and commission Phase E Flight operations (4+ years) and scientific data analysis 48 STELLAR CLASSIFICATION PROGRAM: 49 STELLAR CLASSIFICATION PROGRAM Kepler Input Catalog: Spectroscopic measurements and modeling to determine spectral type and size for all stars in the FOV with V<15 Identify and eliminate magnetically active, young, unevolved stars FOLLOW-UP OBSERVING PROGRAM: 50 FOLLOW-UP OBSERVING PROGRAM Eliminate grazing eclipsing binaries and white dwarfs: Radial velocity measurements to eliminate stellar companions Determine mass of transiting giant planets: Radial velocity measurements for M>0.5 MJ Determine density for transiting giant: Use measured mass and size Search for additional non-transiting giant planets in system: Radial velocity measurements Determine detailed stellar properties (all stars with planets and for a control set): Mass, size, distance, metallicity, luminosity, multiplicity (binary, etc.) Eliminate background objects: Look in Kepler data for change in point spread function during “transit” due to background transiting giant planet or eclipsing binary High spatial resolution image: HST, WST or ground based adaptive optics POWER SPECTRUM OF SUN FROM SMM DATA FOR 1985-1989: 51 POWER SPECTRUM OF SUN FROM SMM DATA FOR 1985-1989 The intrinsic brightness fluctuations are expected to range from 10-3 at the rotation period of the star (~weeks) due to the presence of large star spot groups to <10-5 with a duration of hours due to turbulent motions and gravity waves in the stellar photosphere (Fröhlich, 1987). Brightness changes with durations greater than 16 hours will have little affect on the detectability of transits. INFORMATION OBTAINED FROM PLANETARY TRANSITS: 52 INFORMATION OBTAINED FROM PLANETARY TRANSITS Planet size: From relative brightness change and stellar size Orbital size: From orbital period and stellar mass using Kepler’s Third Law Characteristic planet temperature: From orbit size and stellar luminosity Frequency of planet formation for broad range of stellar types: From ensemble of planetary systems Distribution of planetary sizes, orbital sizes, coplanarity, effects of Jovian planets: From ensemble of planetary systems Frequency and orbits of planets in multiple stellar systems (binaries, etc.): From ensemble of planetary systems Additional science relating to planet habitability: Stellar activity (star spot cycles, p-mode oscillations, white light flaring, etc.) Frequency of Maunder minimums and the implications for the Earth’s climate Stellar rotation rates and limb darkening NUMBER OF DWARF STARS FOR WHICH PLANETS CAN BE DETECTED: 53 NUMBER OF DWARF STARS FOR WHICH PLANETS CAN BE DETECTED The solid lines show the number of dwarf stars of each spectral type for which a planet of a given radius can be detected at ≥8s. The conservative numbers are based on 4 near-grazing transits with a 1 yr period and stars with V≤14. The dashed lines show a significant increase in the number of stars when assuming 4 near-central transits with a 1-yr period. An even greater increase is realized for 8 near-grazing transits with a 0.5-yr period. TRANSIT PROPERTIES FOR SOLAR SYSTEM OBJECTS: 54 TRANSIT PROPERTIES FOR SOLAR SYSTEM OBJECTS Orbital Semi- Transit Transit Geometric Inclination Prob Period Major Axis Duration Depth Probability Invariant pl sec Det Planet P (yrs) a (A.U .) (hours) (% ) (%) f (deg) (%) Mercury 0.241 0.39 8.1 0.0012 1.19 6.33 15 Venus 0.615 0.72 11.0 0.0076 0.65 2.16 23 Earth 1.00 1.00 13. 0.0084 0.47 1.65 22 Mars 1.88 1.52 16 0.0024 0.31 1.71 14 Jupiter 11.86 5.2 30 1.01 0.089 0.39 18 Saturn 29.5 9.5 40 0.75 0.049 0.87 4 Uranus 84.0 19.2 57 0.135 0.024 1.09 2 Neptune 164.8 30.1 71 0.127 0.015 0.72 2 Dependency P2M* = a3 13d*( a/M*)1/2 ∆L/L=Ap/A* d*/D f 4 d* πf D Note: M* is in solar masses; Ap is the area of the planet.