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NASA's Kepler Mission: Searching for Earth-Analogues in Space

The Kepler mission is a space telescope designed to find Earth-analogues within the habitable zone of Sun-like stars using the transit method. It has observed approximately 160,000 stars over 3.5-4 years with high precision. The mission aims to determine the size, composition, and frequency of planets outside our solar system.

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NASA's Kepler Mission: Searching for Earth-Analogues in Space

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  1. NASA’sKepler 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 3.5 - 4 yrs • 20 -30 ppm precision (Earth-size transit: 85 ppm) Science P.I.: Bill Borucki NASA / AMES

  2. Kepler’s Third Law:Square of orbital period is proportional to cube of semi-major axis: P2~ a3 • 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.

  3. Kepler’s orbit

  4. 42(!) CCD detectors 95 megapixels 105 degree2 FOV

  5. Kepler’s in-flight performance:

  6. Kepler’s in-flight performance:

  7. The problem with FALSE POSITIVES: • No planet at all: • Background eclipsing binaries • Multiple systems with one eclipsing binary • Grazing eclipses of binary stars • A transit of a MS star in front of a giant star • Wrong planet: • Giant planet transits a background MS star • Giant planet transits a giant star

  8. Centroid Shift Analysis:

  9. 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 RVfor small planets Transit Observations Test for triples Combined with tests from Kepler data Occultations Centroid motion McDonald 2.7m

  10. dRV [ cm / s ] Follow-up Observing Program (FOP):

  11. 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 ~ 100 2010: 65 hours of planet confirmation obs. >11 candidates (soon to be Kepler planets!)

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

  13. Kepler 7b: The „Styrofoam“ planet Period: 4.88 d Mass: 0.433 MJup Radius: 1.84 RJup Density: 0.16 g cm–3

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

  15. The February 2011 Data Release: • First 4 months of science data • Light curves for ~ 156,000 stars! • 1200+ planet candidates

  16. Comparison of Kepler Result with Theory Lin & Ida ApJ 604 388 2004 From here on, if I say “Kepler Planet” I mean “Kepler Planet Candidates”. Rocky planets Icy planets Gas Giants

  17. Comparison of Kepler Result with Theory Mordasini, Alibert & Benz, A&A 501 1131 2009 Gas Giants Icy planets Rocky Planets

  18. 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 Kp<15,Teff=4100-6100 and log g = 4.0-4.9. Estimates are incomplete for planet radii < 2.0 RE. Get power-law fit of with and

  19. Kepler Planet Occurrence Rates(Howard et al. 2011) 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?

  20. Kepler Planet Occurrence Rates(Howard et al. 2011) Expand the sample to Teff = 3600-7100. Include only targets for which photometric noise permits discovery of planets of 2RE. The planet occurrence rate for small planets (2-4 RE) rises dramatically with decreasing Teff.

  21. 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

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

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

  24. Kepler Multi-Planet System Architectures

  25. Kepler-10b R = 1.4 Rearth Period = 0.83 d Transit Depth: 0.00015 Batalha et al. 2011

  26. Kepler-10b Batalha et al. 2011

  27. CoRoT-7b Kepler-10b 10 Iron enriched Earth-like 7 Earth Mercury r (gm/cm3) No iron 5 Venus Mars 4 3 Moon 2 From Diana Valencia 1 2 1.8 0.4 0.2 1 0.6 0.8 1.2 1.4 1.6 Radius (REarth)

  28. CoRoT-7b Kepler-10b Mstar = 0.91 ±0.03 Msun Rstar = 0.82 ±0.04 Rsun MPl = 7.3 ±1.35 MEarth RPl = 1.58 ±0.10 REarth rPl = 10.2 ±2.7 cgs Mstar = 0.895 ± 0.06 Msun Rstar = 1.056 ±0.02 Rsun MPl = 4.56 ±1.23 MEarth RPl = 1.416 ±0.025 REarth rPl = 8.8 ±2.5 cgs

  29. Kepler-11 Lissauer et al. 2011

  30. 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.

  31. Kepler-11 planet properties

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