1. The Search for Exomoons
David Kipping, UCL
23th September 2008
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.
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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.
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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.
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5. Motivation Detection Methods The TDV Effect
Why Look for Exomoons?
A novel detection and proof of principle.
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6. Motivation Detection Methods The TDV Effect
Why Look for Exomoons?
A novel detection and proof of principle.
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7. Why Look for Exomoons? A novel detection and proof of principle.
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
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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.
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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
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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.
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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.
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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
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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.
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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.
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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
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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.
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17. Motivation Detection 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)
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18. Motivation Detection 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
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19. Motivation Detection 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
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20. Motivation Detection 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.
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21. Motivation Detection 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.
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22. Motivation Detection 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.
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23. Motivation Detection Methods The TDV Effect
Occultation?
Could we look for the dip in star light due to an exomoon’s shadow?
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24. Motivation Detection Methods The TDV Effect
The Transit Method
Winn et al. 2008
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25. Motivation Detection Methods The TDV Effect
Occultation?
Planet transit + Exomoon transit
Simon et al. 2007
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26. Motivation Detection 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
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27. Motivation Detection Methods The TDV Effect
Occultation?
Problem 2: Average position of moon results in lightcurves overlapping: indistinguishable.
Cabrera & Schneider 2005
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28. Motivation Detection 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.
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29. Motivation Detection Methods The TDV Effect
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30. Motivation Detection Methods The TDV Effect
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31. Motivation Detection Methods The TDV Effect
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32. Transit Time Variation (TTV)
Motivation Detection Methods The TDV Effect
Transit Time Variation (TTV)
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33. Transit Time Variation (TTV)
Motivation Detection Methods The TDV Effect
Transit Time Variation (TTV)
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34. Transit Time Variation (TTV)
Motivation Detection Methods The TDV Effect
Transit Time Variation (TTV)
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35. Transit Time Variation (TTV)
Motivation Detection Methods The TDV Effect
Transit Time Variation (TTV)
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36. Motivation Detection Methods The TDV Effect
The Problem with TTV
Lots of things can cause TTV, not just exomoons.
Prof. Holman called this the ‘inverse-problem’.
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37. Motivation Detection 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  MMOON aMOON
1 measureable, 2 unknowns => Can’t solve!
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38. Motivation Detection Methods The TDV Effect
The Transit Method
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39. Motivation Detection Methods The TDV Effect
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40. Transit Duration Variation (TDV)
Motivation Detection Methods The TDV Effect
Transit Duration Variation (TDV)
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41. Transit Duration Variation (TDV)
Motivation Detection Methods The TDV Effect
Transit Duration Variation (TDV)
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42. Transit Duration Variation (TDV)
Motivation Detection Methods The TDV Effect
Transit Duration Variation (TDV)
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43. TTV + TDV = A Unique Signature
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.
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44. Motivation Detection Methods The TDV Effect
Sensitivity
An Earth mass exomoon is detectable from the ground with current instruments!
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45. The Holy Grail of Exomoons
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!
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