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The Search for Exomoons

23 th September 2008. The Search for Exomoons. David Kipping, UCL. Acknowledgements: Giovanna Tinetti, Alan Aylward, Ignasi Ribas, Jean-Philippe Beaulieu, Steve Fossey, the HOLMES collaboration. Motivation Detection Methods The TDV Effect. What is an Exomoon ?.

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The Search for Exomoons

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  1. 23th September 2008 The Search for Exomoons David Kipping, UCL Acknowledgements: Giovanna Tinetti, Alan Aylward, Ignasi Ribas, Jean-Philippe Beaulieu, Steve Fossey, the HOLMES collaboration

  2. Motivation Detection Methods The TDV Effect What is an Exomoon? • A smaller, natural satellite that orbits an extrasolar planet. Molecules 2008, D. Kipping 2/18

  3. Motivation Detection Methods The TDV Effect What is an Exomoon? • A smaller, natural satellite that orbits an extrasolar planet. • There are no known exomoons, but their existence is theorized around many exoplanets. Molecules 2008, D. Kipping 2/18

  4. Motivation Detection Methods The TDV Effect What is an Exomoon? • A smaller, natural satellite that orbits an extrasolar planet. • There are no known exomoons, but their existence is theorized around many exoplanets. Molecules 2008, D. Kipping 2/18

  5. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Molecules 2008, D. Kipping 3/18

  6. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Molecules 2008, D. Kipping 3/18

  7. Motivation Current Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Sartoretti & Schneider 1999 Szabo et al. 2006 Simon et al. 2007 Kipping 2008 Molecules 2008, D. Kipping 3/18

  8. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Exomoons are likely to be < MEARTH and rocky. Molecules 2008, D. Kipping 3/18

  9. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Exomoons are likely to be < MEARTH and rocky. Belbruno & Gott 2005 Valencia et al. 2006 Canup & Ward 2007 Molecules 2008, D. Kipping 3/18

  10. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Exomoons are likely to be < MEARTH and rocky. Complex life may not form on exoplanets without large moons. Molecules 2008, D. Kipping 3/18

  11. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Exomoons are likely to be < MEARTH and rocky. Complex life may not form on exoplanets without large moons. Molecules 2008, D. Kipping 3/18

  12. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection and proof of principle. Exomoons are likely to be < MEARTH and rocky. Complex life may not form on exoplanets without large moons. Laskar et al. 1993 Ward & Brownlee 2000 Waltham 2004 Lathe 2005 Molecules 2008, D. Kipping 3/18

  13. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection. Exomoons are likely to be < MEARTH. Complex life may not form on exoplanets without large moons. There may be more habitable exomoons than exoplanets. Molecules 2008, D. Kipping 3/18

  14. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection. Exomoons are likely to be < MEARTH. Complex life may not form on exoplanets without large moons. There may be more habitable exomoons than exoplanets. Molecules 2008, D. Kipping 3/18

  15. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection. Exomoons are likely to be < MEARTH. Complex life may not form on exoplanets without large moons. There may be more habitable exomoons than exoplanets. Scharf 2008 Thommes et al. 2008 Molecules 2008, D. Kipping 3/18

  16. Motivation Detection Methods The TDV Effect Why Look for Exomoons? A novel detection. Exomoons are likely to be < MEARTH. Complex life may not form on exoplanets without large moons. There may be more habitable exomoons than exoplanets. Implications for planetary formation theory. Molecules 2008, D. Kipping 3/18

  17. MotivationDetection Methods The TDV Effect Direct Imaging? • Brightness ratio  1:1010. • An Earth-sized body 0.02 micro arcseconds. • Current interferometric precision 25 micro arcseconds (Baines et al. 2007) Molecules 2008, D. Kipping 4/18

  18. MotivationDetection Methods The TDV Effect Direct Imaging? • Brightness ratio  1:1010. • An Earth-sized body 0.02 micro arcseconds. • Current interferometric precision 25 micro arcseconds (Baines et al. 2007) NWO Proposal Molecules 2008, D. Kipping 4/18

  19. MotivationDetection Methods The TDV Effect Direct Imaging? • Brightness ratio  1:1010. • An Earth-sized body 0.02 micro arcseconds. • Current interferometric precision 25 micro arcseconds (Baines et al. 2007) • => Directly imaging an exomoon is currently impossible. NWO Proposal Molecules 2008, D. Kipping 4/18

  20. MotivationDetection Methods The TDV Effect Radial Velocity? • Radial velocity (Doppler spectroscopy) measures the wobble of the host star due to a planet. • This method would be insensitive to a planet + moon system. Molecules 2008, D. Kipping 5/18

  21. MotivationDetection Methods The TDV Effect Radial Velocity? • Radial velocity (Doppler spectroscopy) measures the wobble of the host star due to a planet. • This method would be insensitive to a planet + moon system. Molecules 2008, D. Kipping 5/18

  22. MotivationDetection Methods The TDV Effect Radial Velocity? • Radial velocity (Doppler spectroscopy) measures the wobble of the host star due to a planet. • This method would be insensitive to a planet + moon system. • => Radial velocity cannot be used to detect exomoons. Molecules 2008, D. Kipping 5/18

  23. MotivationDetection Methods The TDV Effect Occultation? • Could we look for the dip in star light due to an exomoon’s shadow? Molecules 2008, D. Kipping 6/18

  24. MotivationDetection Methods The TDV Effect The Transit Method Winn et al. 2008 Molecules 2008, D. Kipping 7/18

  25. MotivationDetection Methods The TDV Effect Occultation? • Planet transit + Exomoon transit Simon et al. 2007 Molecules 2008, D. Kipping 8/18

  26. MotivationDetection Methods The TDV Effect Occultation? • Problem 1: Transit of moon is very small. • Require space-based telescope to do 2.5 MEARTH. Ballard et al. 2008 Molecules 2008, D. Kipping 8/18

  27. MotivationDetection Methods The TDV Effect Occultation? • Problem 2: Average position of moon results in lightcurves overlapping: indistinguishable. Cabrera & Schneider 2005 Molecules 2008, D. Kipping 8/18

  28. MotivationDetection Methods The TDV Effect Occultation? • Could we look for the dip in star light due to an exomoon’s shadow? • => Possible, but somewhat insensitive to low mass objects. Molecules 2008, D. Kipping 9/18

  29. MotivationDetection Methods The TDV Effect Molecules 2008, D. Kipping 10/18

  30. MotivationDetection Methods The TDV Effect Molecules 2008, D. Kipping 11/18

  31. MotivationDetection Methods The TDV Effect Molecules 2008, D. Kipping 12/18

  32. MotivationDetection Methods The TDV Effect Transit Time Variation (TTV) Molecules 2008, D. Kipping 13/18

  33. MotivationDetection Methods The TDV Effect Transit Time Variation (TTV) Molecules 2008, D. Kipping 13/18

  34. MotivationDetection Methods The TDV Effect Transit Time Variation (TTV) Molecules 2008, D. Kipping 13/18

  35. MotivationDetection Methods The TDV Effect Transit Time Variation (TTV) Molecules 2008, D. Kipping 13/18

  36. MotivationDetection Methods The TDV Effect The Problem with TTV • Lots of things can cause TTV, not just exomoons. • Prof. Holman called this the ‘inverse-problem’. Molecules 2008, D. Kipping 14/18

  37. MotivationDetection Methods The TDV Effect The Problem with TTV • Lots of things can cause TTV, not just exomoons. • Prof. Holman called this the ‘inverse-problem’. • TTV  MMOONaMOON • 1 measureable, 2 unknowns => Can’t solve! Molecules 2008, D. Kipping 14/18

  38. Motivation Detection Methods The TDV Effect The Transit Method Molecules 2008, D. Kipping (7/18)

  39. Motivation Detection Methods The TDV Effect Molecules 2008, D. Kipping (12/18)

  40. Motivation Detection Methods The TDV Effect Transit Duration Variation (TDV) Molecules 2008, D. Kipping 15/18

  41. Motivation Detection Methods The TDV Effect Transit Duration Variation (TDV) Molecules 2008, D. Kipping 15/18

  42. Motivation Detection Methods The TDV Effect Transit Duration Variation (TDV) Molecules 2008, D. Kipping 15/18

  43. Motivation Detection Methods The TDV Effect TTV + TDV = A Unique Signature • The TDV signals lags behind the TTV signal by 90o. • TTV  TDV  1-10 seconds . • TTV and TDV allow you to solve for both the mass and orbital radius of the exomoon. Molecules 2008, D. Kipping 16/18

  44. Motivation Detection Methods The TDV Effect Sensitivity • An Earth mass exomoon is detectable from the ground with current instruments! Molecules 2008, D. Kipping 17/18

  45. Motivation Detection Methods The TDV Effect The Holy Grail of Exomoons • Consider a Neptune –like planet around an M-dwarf on a 35-day period => Goldilocks zone. • Consider an Earth mass exomoon orbiting this planet. • TTV  140s and TDV  60s. • Typical TTV error  10s • Typical TDV error  20s. • => Very secure detection of a habitable Earth-like body! Molecules 2008, D. Kipping 18/18

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