Why Search for Extrasolar Planets?

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2 Why Search for Extrasolar Planets? What is the diversity of habitats for life in the universe? Are Earth-like planets common or rare in our region of the galaxy? We have an elaborate and self-consistent theory for the formation of our own solar system, but It was based on just the single example of the system in which we live. Is our Solar System the proper paradigm for planetary system formation and evolution? Is planetary system formation a common natural result of star formation?

3 NASA s Kepler mission in a nutshell designed to find Earth-analogues (inside the habitable zone of Sun-like stars) Space telescope => continuous obs. / no atmosphere using transit method (+ ground-based FU) ~160,000 stars over yrs ppm precision (Earth-size transit: 85 ppm) Science P.I.: Bill Borucki NASA / AMES

4 Transit Frequency gives us ORBIT SIZE Orbit Size with Star Temperature tells us if planet is in habitable zone. Transit duration, depth, gives us PLANET SIZE Size and Mass (with a doppler measurement of the wobble ) gives DENSITY Density is clue to COMPOSITION.

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7 Kepler s orbit

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9 42(!) CCD detectors 95 megapixels 105 degree 2 FOV

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11 Kepler s in-flight performance:

12 Kepler s in-flight performance:

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15 The problem with FALSE POSITIVES: No planet at all: 1. Background eclipsing binaries 2. Multiple systems with one eclipsing binary 3. Grazing eclipses of binary stars 4. A transit of a MS star in front of a giant star Wrong planet: Wrong planet: 5. Giant planet transits a background MS star 6. Giant planet transits a giant star

16 Centroid Shift Analysis:

17 Follow-Up Observation Program Imaging (Standard, AO, Speckle, HST?) Removes confusion due to crowding Spectroscopy Low-Res removes some false positives (e.g., binaries) High-Res can measure mass of some planets Upper limit to RV for small planets Transit Observations Test for triples Combined with tests from Kepler data Occultations Centroid motion McDonald 2.7m

18 Follow-up Observing Program (FOP): drv [ cm / s ]

19 McDonald Observatory: Harlan J. Smith 2.7 m Telescope / Tull Coude Spectrograph 2 years of recon spectroscopy of several hundreds of Kepler candidates (V ~ 11 to 16) March to November Hobby-Eberly 9 m Telescope (HET) / HRS Super-recons S/N ~ : 65 hours of planet confirmation obs. >11 candidates (soon to be Kepler planets!)

20 Harlan J. Smith 2.7 m Telescope & Tull spectrograph Reconnaissance Spectroscopy :

21 Final step: RV determination of planetary orbit Keck/HIRES RVs (Geoff Marcy et al.)

22 Kepler 7b: The Styrofoam planet Period: 4.88 d Mass: MJup Radius: 1.84 RJup Density: 0.16 g cm 3

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24 Kepler planets confirmed in Texas: Endl et al. (2011) Desert et al. (2011) more to come soon.

25 The February 2011 Data Release: First 4 months of science data Light curves for ~ 156,000 stars! planet candidates

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33 Comparison of Kepler Result with Theory Lin & Ida ApJ From here on, if I say Kepler Planet I mean Kepler Planet Candidates. Rocky planets Icy planets Gas Giants

34 Comparison of Kepler Result with Theory Mordasini, Alibert & Benz, A&A Gas Giants Icy planets Rocky Planets

35 Kepler Planet Occurrence Rates (Howard et al. 2011) Occurrence rates take into account the actual observed S/N on each star. Consider only Kepler candidates in the range K p <15,T eff = and log g = Estimates are incomplete for planet radii < 2.0 R E. df ( R)! k R d log R Get power-law fit of with k = +0.5 = R and R 2.9 " = #1.92 ± 0.11 "0.4

36 Kepler Planet Occurrence Rates (Howard et al. 2011) R p (R E ) P < 10 days P < 50 days 2-4 R E 0.025± ± R E 0.005± ± R E 0.004± ± R E 0.034± ±0.008 The occurrence rate of hot Jupiters in the Kepler field is only 40% that of the solar neighborhood. Is Kepler sampling the same population of stars as RV surveys?

37 Kepler Planet Occurrence Rates (Howard et al. 2011) Expand the sample to T eff = Include only targets for which photometric noise permits discovery of planets of 2R E. The planet occurrence rate for small planets (2-4 R E ) rises dramatically with decreasing T eff. f ( T eff) = " # % $ T " 5100K & 1000K ( ' eff

38 Kepler Multi-Planet System Statistics Kepler Singles Kepler Multiples CoRoT Singles Kepler finds very few giant planets in systems of multiple planets Latham et al. ApJL in press 2011

39 1. Planets smaller than Neptune dominate single and multiple transiting systems, but more so for multiples (68% for singles but 86% for multiples) Preliminary evidence indicates that up to 30% of stars may have closely packed planetary systems of superearths 2. Singles may be more common around hotter stars (i.e. more massive)

40 Kepler Multi-Planet System Architectures Lissauer et al. ApJ submitted 2011

41 Kepler Multi-Planet System Architectures Candidates per system or more 1 Total stars Total planets 1184 Total stars with planets 946 MMR Total Pairs Adjacent Pairs 2: : : : : : : :7 3 3

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43 Kepler-10b R = 1.4 Rearth Period = 0.83 d Transit Depth: Batalha et al. 2011

44 Kepler-10b Batalha et al. 2011

45 CoRoT-7b ρ (gm/cm 3 ) Mercury Moon Mars Earth Venus Kepler-10b Iron enriched No iron Earth-like 2 From Diana Valencia Radius (R Earth )

46 CoRoT-7b Kepler-10b M star = 0.91 ±0.03 M sun R star = 0.82 ±0.04 R sun M Pl = 7.3 ±1.35 M Earth R Pl = 1.58 ±0.10 R Earth ρ Pl = 10.2 ±2.7 cgs M star = ± 0.06 M sun R star = ±0.02 R sun M Pl = 4.56 ±1.23 M Earth R Pl = ±0.025 R Earth ρ Pl = 8.8 ±2.5 cgs

47 Kepler-11 Lissauer et al. 2011

48 The mutual gravitational influence of the planets causes transit timing variations (TTVS): the transit of an individual planet occurs at slightly different times than expected. From these TTVs one can model the dynamics of the system and determine the planet mass. This is the first system whose planets masses were determined without Doppler measurements.

49 Kepler-11 planet properties

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55 Summary Current status: Kepler has released Q0-Q2 lightcurves on 155,453 stars and on the 1,235 planet candidates that it has discovered in the first four months of science operations. The planetary candidates include 68 of Earth-size, 288 of super-earth-size, 662 of Neptune-size, and 165 of Jupiter-size. 170 stars show the presence of systems of transiting planetary candidates. Kepler continues to make excellent progress toward its goal of determining the frequency of Earth-size planets.