The Search for Exomoons

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
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What is an Exomoon?
Motivation Detection Methods
The TDV Effect

• A smaller, natural satellite that orbits an
  extrasolar planet.

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What is an Exomoon?
Motivation Detection Methods
The TDV Effect

• 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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What is an Exomoon?
Motivation Detection Methods
The TDV Effect

• 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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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.

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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.

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Why Look for Exomoons?
Motivation Current Methods
The TDV Effect

1. A novel detection and proof of principle.

Sartoretti Schneider 1999
Szabo et al. 2006
Simon et al. 2007
Kipping 2008
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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.
2. Exomoons are likely to be lt MEARTH and rocky.

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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.
2. Exomoons are likely to be lt MEARTH and rocky.

Belbruno Gott 2005
Valencia et al. 2006
Canup Ward 2007
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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.
2. Exomoons are likely to be lt MEARTH and rocky.
3. Complex life may not form on exoplanets without
   large moons.

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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.
2. Exomoons are likely to be lt MEARTH and rocky.
3. Complex life may not form on exoplanets without
   large moons.

Molecules 2008, D. Kipping
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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection and proof of principle.
2. Exomoons are likely to be lt MEARTH and rocky.
3. 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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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection.
2. Exomoons are likely to be lt MEARTH.
3. Complex life may not form on exoplanets without
   large moons.
4. There may be more habitable exomoons than
   exoplanets.

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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection.
2. Exomoons are likely to be lt MEARTH.
3. Complex life may not form on exoplanets without
   large moons.
4. There may be more habitable exomoons than
   exoplanets.

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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection.
2. Exomoons are likely to be lt MEARTH.
3. Complex life may not form on exoplanets without
   large moons.
4. There may be more habitable exomoons than
   exoplanets.

Scharf 2008
Thommes et al. 2008
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Why Look for Exomoons?
Motivation Detection Methods
The TDV Effect

1. A novel detection.
2. Exomoons are likely to be lt MEARTH.
3. Complex life may not form on exoplanets without
   large moons.
4. There may be more habitable exomoons than
   exoplanets.
5. Implications for planetary formation theory.

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Direct Imaging?
Motivation Detection Methods
The TDV Effect

• Brightness ratio ? 11010.
• An Earth-sized body ?0.02 micro arcseconds.
• Current interferometric precision ?25 micro
  arcseconds (Baines et al. 2007)

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Direct Imaging?
Motivation Detection Methods
The TDV Effect

• Brightness ratio ? 11010.
• An Earth-sized body ?0.02 micro arcseconds.
• Current interferometric precision ?25 micro
  arcseconds (Baines et al. 2007)

NWO Proposal
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Direct Imaging?
Motivation Detection Methods
The TDV Effect

• Brightness ratio ? 11010.
• An Earth-sized body ?0.02 micro arcseconds.
• Current interferometric precision ?25 micro
  arcseconds (Baines et al. 2007)
• gt Directly imaging an exomoon is currently
  impossible.

NWO Proposal
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Radial Velocity?
Motivation Detection Methods
The TDV Effect

• 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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Radial Velocity?
Motivation Detection Methods
The TDV Effect

• 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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Radial Velocity?
Motivation Detection Methods
The TDV Effect

• 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.
• gt Radial velocity cannot be used to detect
  exomoons.

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Occultation?
Motivation Detection Methods
The TDV Effect

• Could we look for the dip in star light due to an
  exomoons shadow?

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The Transit Method
Motivation Detection Methods
The TDV Effect
Winn et al. 2008
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Occultation?
Motivation Detection Methods
The TDV Effect

• Planet transit Exomoon transit

Simon et al. 2007
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Occultation?
Motivation Detection Methods
The TDV Effect

• 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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Occultation?
Motivation Detection Methods
The TDV Effect

• Problem 2 Average position of moon results in
  lightcurves overlapping indistinguishable.

Cabrera Schneider 2005
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Occultation?
Motivation Detection Methods
The TDV Effect

• Could we look for the dip in star light due to an
  exomoons shadow?
• gt Possible, but somewhat insensitive to low mass
  objects.

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Motivation Detection Methods
The TDV Effect
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Motivation Detection Methods
The TDV Effect
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Motivation Detection Methods
The TDV Effect
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Transit Time Variation (TTV)
Motivation Detection Methods
The TDV Effect
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Transit Time Variation (TTV)
Motivation Detection Methods
The TDV Effect
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Transit Time Variation (TTV)
Motivation Detection Methods
The TDV Effect
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Transit Time Variation (TTV)
Motivation Detection Methods
The TDV Effect
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The Problem with TTV
Motivation Detection Methods
The TDV Effect

• Lots of things can cause TTV, not just exomoons.
• Prof. Holman called this the inverse-problem.

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The Problem with TTV
Motivation Detection Methods
The TDV Effect

• Lots of things can cause TTV, not just exomoons.
• Prof. Holman called this the inverse-problem.
• TTV ? MMOON aMOON
• 1 measureable, 2 unknowns gt Cant solve!

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The Transit Method
Motivation Detection Methods
The TDV Effect
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Motivation Detection Methods
The TDV Effect
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Transit Duration Variation (TDV)
Motivation Detection Methods
The TDV Effect
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Transit Duration Variation (TDV)
Motivation Detection Methods
The TDV Effect
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Transit Duration Variation (TDV)
Motivation Detection Methods
The TDV Effect
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TTV TDV A Unique Signature
Motivation Detection Methods
The TDV Effect

• 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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Sensitivity
Motivation Detection Methods
The TDV Effect

• An Earth mass exomoon is detectable from the
  ground with current instruments!

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The Holy Grail of Exomoons
Motivation Detection Methods
The TDV Effect

• Consider a Neptune like planet around an M-dwarf
  on a 35-day period gt Goldilocks zone.
• Consider an Earth mass exomoon orbiting this
  planet.
• TTV ? 140s and TDV ? 60s.
• Typical TTV error ? 10s
• Typical TDV error ? 20s.
• gt Very secure detection of a habitable
  Earth-like body!

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