KEPLER: The Search for Earth-size Planets in the Habitable Zone of Solar-like Stars

2 WB/lct Gibor Basri, U. Cal., Berkeley Alan Boss, Carneige Inst. W. Timothy Brown, HAO, UCAR Donald Brownlee, U. Wash. John Caldwell, York U. Christensen-Dalsgaard, Arhus U. William Cochran, U. Texas Edna Devore, SETI Institute Edward Dunham, Lowell Obs. Andrea Dupree, CfA, SAO T. Nick Gautier, JPL John Geary, CfA, SAO Ronald Gilliland, STScI Alan Gould, Lawrence Hall of Sci. Steve Howell, U. Ariz Jon M. Jenkins, SETI Institute Yoji Kondo, NASA GSFC David Latham, CfA, SAO Jack Lissauer, NASA Ames Geoff Marcy, U. Cal., Berkeley David Monet, U.S. Naval Obs. David Morrison, NASA Ames Tobias Owen, U. of Hawaii Harold Reitsema, Ball Aerospace Dmiter Sasselov, CfA, SAO Jill Tarter, SETI Institute William J. Borucki, PI, and David Koch, Deputy PI SCIENCE TEAM

3 WB/lct CHARACTERISTICS OF EXO PLANETS Most planets are inside of 2 AU Many planets heavier than Jupiter 15% of systems have > 2 Jupiters  Jupiters must form readily Most orbits have high eccentricity Giant planet migration & scattering remove small planets Lineweaver claims >10% of stars have giant planets  Earths might be rare

4 WB/lct KEY QUESTIONS: Are terrestrial planets common or rare? What are their sizes & distances? How often are they in the habitable zone? What is their dependence on stellar properties?

5 WB/lct SCIENTIFIC OBJECTIVES Frequency of terrestrial and larger planets in & near the habitable zone of a wide variety of stellar spectral types Distribution of sizes & semi-major axes of these planets Characterisitics of additional members of each planetary system by using other techniques Distributions of semi-major axis, albedo, size, and density of short-period giant planets Occurrence frequency and orbital distribution of planets orbiting multiple star systems Characteristics of stars that harbor planetary systems Determine the :

6 WB/lct REQUIRED SENSITIVITY ∆L/L = area Earth/area Sun = 1/12,000 = 8x10 -5 Require total noise <2x10 -5 for 4-  detection in 6.5 hours Three sources of noise and their contributions: - Stellar variability:<1x10 -5, Sun on timescale of ~1/2 day - Shot noise:1.4x10 -5, in 6.5 hr for m v =12 solar-like star and 0.95-meter aperture - Instr. noise: <1x10 -5, includes dark current, read noise, thermal effects, pointing jitter, & shutterless operation. Detectors: 42 2k x1k format CCDs with dual readout - Thinned, back-illuminated, & anti-reflection coated Brightest m v =9 and full-well depth of 10 6 e - requires: - Soft image and readout every 6 seconds.

7 WB/lct MEASUREMENT TECHNIQUE Use differential photometry (common mode rejection): - Stellar flux is re-normalized to the ensemble of thousands of stars in each half of each CCD & readout with a single amplifier; Transits only last several hours: - Long term photometric stability is not necessary; Star image covers 25 pixels: - Mitigates saturation (10 9 e - /hr) and sensitivity to motion; Control pointing to 3 millipixels (0.01 arc sec); - Images remain on the same pixels; Operate CCDs near full-well capacity at low temperature: - Dark current and read-noise effects negligible; - Minimizes damage by GCR & solar proton events; Photometer in a heliocentric orbit (like Spitzer): - Provides stable thermal and stray light environment.

8 WB/lct Use transit photometry to detect Earth-size planets  0.95 meter aperture provides enough photons  Observe for several years to detect transit patterns  Monitor a single FOV continuously to avoid missing transits  Use heliocentric orbit MISSION APPROACH Kepler: A Wide FOV Photometer to Monitor 100,000 Stars for 4 yrs that can Detect Earth-size Planets in the HZ Get statistically valid results by monitoring 100,000 dwarf stars Wide FOV telescope Large array of CCD detectors

9 WB/lct MISSION FEATURES Designed to find hundreds of Earth-size and larger planets Stellar classification for targets Ground-based observations rule out false positives Single science instrument: Photometer: 0.95m aperture, 42 CCDs, nm, passive cooling, focusable primary FOV: 100 sq deg. centered & fixed at 19h23m, 44º 30’ Launch Vehicle: Delta L Launch date: June 2008 Operational life: 4 years with expendables for 6 years

10 WB/lct MERIT FUNCTION (MF) Quantifies science value as f(instrument & mission properties) Mission chosen for the science it could perform => MF score based on currently predicted science performance MF properties Models of planetary systems, instrument specs., detection approach Score is 100 based on currently predicted instrument perform. a)60 pts for planets in HZ, 30 pts for planets outside HZ, 10 pts for p-modes b)Small planets have higher value than bigger (40,20,5,1) c)Outer planets have higher value than inner planets (r 2 ) Adjustable parameters for instrument specs & performance, mission parameters, and surprises of nature

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14 WB/lct STELLAR CLASSIFICATION PROGRAM Multiband photometry of 5x10 6 stars in FOV Calibrate against spectroscopic observation of clusters Get spectral type & luminosity class  Size estimate Choose late type dwarfs for targets Choose only brightest large stars and accept dim small stars to maximize small planet detections

15 WB/lct DETECTION PROTOCOL

16 WB/lct VALIDATION OF DISCOVERIES  SNR > 7 to rule out statistical fluctuations  Three or more transits to confirm orbital characteristics  Light curve depth, shape, and duration  Radial velocity Medium resolution rules out stellar companions High resolution measures mass of giant planets  Image subtraction to identify signals from eclipsing background stars  High spatial resolution Identifies extremely close background stars  Color change during transit identifies bkgd stars

17 WB/lct DETECTION OF SHORT-PERIOD GIANTS Log Radiative PWR

18 WB/lct SCIENCE DRIVER Statistically valid result for abundance of Earth-size planets in habitable zone Expected # of planets found, assuming one planet of a given size & semi-major axis per star and random orientation of orbital planes. # of Planet Detections Orbital Semi-major Axis (AU)

19 WB/lct NUMBER OF TERRESTRIAL PLANETS IN HZ

20 WB/lct NUMBER OF PLANETS FOUND OUTSIDE HZ

21 WB/lct OPPORTUNITIES FOR PARTICIPATION Guest Observer Program Choose targets in FOV 250 stars at 1-min cadence, 3000 stars at 15-min cadence, Continuous for 3 months Data Analysis Program Obtain observations from STScI archive Both differential and instrument magnitudes Participating Scientist Program Propose exoplanet studies that complement science team studies

22 WB/lct SUMMARY & PLANS Phase C/D work is underway. Reduced funding requires delaying the launch by several months. 24 Flight-grade CCDs have been received. Optics are being polished.  Kepler is on track for a June 2008 launch.

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24 WB/lct MOST STARS ARE QUIET ENOUGH –Variability noise declines with rotation rate Magnetic activity declines Spot passage period increases –Solar-type stars slowed enough by 2-3 Gyr Rotation-activity relationship well-known Stellar spin-down timescales well-known –70% of solar-type stars are slow & quiet enough Galaxy >10 Gyr old & star formation ~constant Detailed galactic population models confirm Actual observations of stellar activity confirm

25 WB/lct STARS QUIET ENOUGH TO FIND EARTHS Solar behavior at Kepler timescales and precision is known –ACRIM, DIARAD, VIRGO on SMM, SOHO –Measured throughout solar cycle Transits can be seen despite variability –Short durations (~10 hours) –Well-defined shapes and depths –Highly periodic repetitions

26 WB/lct STELLAR ACTIVITY LEVELS

27 WB/lct HST OBSERVATION OF HD209458b Ten-minute binned data from several orbits have a precision of 60 ppm (Brown et al. 2001).

28 WB/lct OPERATIONS ORGANIZATION

29 WB/lct CONFUSION DUE TO ECLIPSING BINARIES EXPECTED NUMBER OF GRAZING TRANSITS BY TARGET STARS 50% of target stars are binaries => 50,000 targets are binaries 20% have orbital periods of order days to weeks 10,000 stars with transit probabilities near 10% 1000 stars will show stellar transits Of these 1,000 stars, ~ 6.5% (i.e., 65) stars will show 1% deep transits ~ 1.4% (i.e., 14) stars will show 0.1% deep transits ~ 0.3% (i.e., 3) stars will show 0.01% deep transits 20% have orbital periods between a few months and a few years 10,000 stars with transit probabilities near 1% 100 stars will show stellar transits Of these 100 stars; ~ 6.5% (i.e., 6 ) stars will show 1% deep transits ~ 1.4% (i.e., 1.4 ) stars will show 0.1% deep transits ~ 0.3% (i.e., 0.3 ) stars will show 0.01% deep transits

30 WB/lct Transit Signal vs. Solar Noise Time Scale, days Energy&PowerDensityEnergy&PowerDensity 8-hour transit 10-hour transit Solar Min Solar Max