Life at the edge of what is possible with Kepler

A colloquium I gave a UC Berkeley. This was hastily thrown together as I was a replacement speaker. Charlie Townes (inventor of the laser) was sat int he front row.

Transcript

1. Life at the edge of what is possible with Kepler Tom Barclay NASA Ames Research Centre
2. A talk in three parts • What we can learn from the giant planets observed by Kepler • Exploring the smallest planet candidates • Pushing towards a second habitable Earth
3. What is a transit?
4. The Transit Method of finding Exoplanets
5. Transits of exoplanets Orbital Period Size of Planet The light curves tell us the size and orbital period of the planet. The orbital period can be used to estimate the planet’s surface temperature Brightness of Star Time (days)
6. What is needed to find Earth-like planets? • Transit probability somewhere from 0.5 – 3% – We want to look at LOTS of stars • We need very low noise – ideally limited by stellar variability – Go into space far away from the Earth • Observe multiple orbits of the same planet – Stare at the same field continuously for as long as possible So we built a spacecraft and called it Kepler 6
7. We want to look at LOTS of stars 7 • 42 CCDs • 2.25 Mpix each • 115 sq. deg. • 30 min cadence
8. Go into space far away from the Earth 8
9. Stare at the same field continuously
10. Stare at the same field continuously
11. * * March 6, 2009
12. * * Transiting Planets pre-Kepler Orbital Period in days Size Relative to Earth
13. * * Orbital Period in days Jun 2010 Feb 2011 Feb 2012 Candidates as of Jan 2013 Q0-Q8
14. Planet Size vs. T eq - Habitability
15. Why might we be interested in large planets? 15 • Large planets exhibit high signal to noise transits – We can observe tiny effects (<20 ppm) • This allows us to learn about physical characteristic beyond the radius • Some have RV follow-up – We can test our assumptions on these and apply to others We can look at the brightness variations we see as a function of orbital phase
16. What can Kepler bring to large planets 16
17. Phase variations 17
18. Tidally induced ellipsoidal variations 18
19. Doppler beaming 19 • From the reflex motion of the star owing to a planet • Combination of two effects – one relativistic and one classical Classical • As the star moves towards/away us the light is blue/red-shifted • The spectrum of the star moves in/ out of the Kepler passband the star gets brighter/fainter Relativistic • As star moves towards us the light is beamed in our direction • As it moves away light is beamed in other direction, star gets fainter
20. Reflection/emission from the planet 20 Madhusudhan & Burrows 2011
21. Phase variations • Build a simple model (really simple!!) • Assume phase variations are a combination of a few sinusoidal functions 21 Ellipsoidal variations Doppler beaming Reflection/emission from planet Shown here is a Lambertian phase function
22. What we can learn from phase variations 22
23. Occultation (secondary eclipse) 23
24. Using the occultation and reflection 24 The occultation tells us the planet-star contrast. The reflection/emission amplitude tells us the day-night planet contrast
25. Ellipsoidal variations from HAT-P-7b 25 Welsh et al. 2010 Shporer et al. in prep.
26. Kepler-13b 26 Used to derive a mass from beaming of 9.2±1.1 MJup Shporer et al. 2011
27. Phase variations seen from TrES-2b • We detect significant ellipsoidal, beaming and reflection from TrES-2b. • A radial velocity amplitude consistent with ground based RVs Derived planet mass 27 Photometry Ground-based RVs Barclay et al., 2012
28. The darkest exoplanet is even darker • TrES-2b is the darkest known exoplanet – The geometric albedo found by Kipping et al. is 0.025±0.007 • We find a geometric albedo of 0.014±0.003 The darkest known exoplanet is even darker than thought 28 (2011) Barclay et al., submitted
29. Characterizing Small planets • Looking for planets smaller than Mars
30. Thanks!
31. Three planet candidates KOI-245.03 Transit depth of 22 ppm A 13 day orbital period Two other candidates with periods of 21 and 40 days
32. Introducing Kepler-37 • A bright G-type star • Measurable Solar-like oscillation – The densest star for which asteroseismology has been possible Kp = 9.7 Teff = 5400 K R = 0.77 Rsun M = 0.80 Msun
33. BUT are these bone fide planets • Our validation attempt required exquisite follow-up observation • Follow-up was used in a BLENDER analysis Unfortunately this source is saturated which makes centoiding only good to 1 pix BLENDER explores false positive scenarios that could mimic a transit
34. Stunning AO data • FWHM < 0.1’’ • ΔKp > 10 at 1’’ – No other star observed 1’’
35. HIRES data • RV limit of 7 m/s over 2 years • CCF of spectra exclude stars with ΔRV > 10 km/s • Close stellar companions excluded • Bright background stars must have very similar <RV>
36. Calculating a planet prior • BLENDER works by comparing the false positive rate to the probability that the source is a real planet Largest candidate in the system in undoubtedly a planet – Kepler-37d The middle planet is a planet orbiting the target with a probability >99.95% – Kepler-37c
37. Planet prior for the small one • No population of planet candidates as small as KOI-245.03 – no comparison for planet prior We assume the occurrence rate of small planets is the same as for Earth-size planet With this assumption KOI-245.03 is a planet with a probability >99.95% – Kepler-37b
39. Kepler-37b is not a dwarf planet • A planet orbits the Sun a star • Is a nearly round shape • Has cleared its neighborhood The minimum mass for Kepler-37b is around 0.01 M ⊕ Therefore the planet must be ‘a nearly round shape’ Soter 2006
40. Enough of these hot planets! • The ultimate goal of the Kepler mission is to find Earth- size habitable planets around Sun-like stars
41. But what is the habitable zone? • A somewhat amorphous concept • Liberally 175-310 K • Conservatively 185-270 K Kopparapu et al. 2013
42. Kepler-69 • A Sun-like star (G4V) • Host to two planets • Kepler-69b – Porb=13 days – 2.3 Rearth • Kepler-69c – Porb=242 days – 1.74 Rearth • Detection very difficult because of image artifacts Barclay et al, 2013
44. Planet validation • We exclude false positive using Kepler data, Keck RVs and hi-res imaging
45. A possibly habitable zone planet • Kepler-69c is the first super-earth- sized planet in (or near to?) the habitable zone of a Sun-like star • Teq = 283+/-17 K
46. Conclusion?
 
 
 We are at the cusp of finding the first truly 
 Earth-like planet