David
Kipping, UCL
th
23 September 2008
Acknowledgements: Giovanna Tinetti, Alan Aylward, Ignasi Ribas,
Jean-Philippe Beaulieu, Steve Fossey, the HOLMES collaboration
Motivation
Detection Methods
The TDV Effect
• A smaller, natural satellite that orbits an extrasolar
planet.
2/18
Molecules 2008, D. Kipping
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.
2/18
Molecules 2008, D. Kipping
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.
2/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
3/18
Molecules 2008, D. Kipping
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
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
2. Exomoons are likely to be < MEARTH and rocky.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
2. Exomoons are likely to be < MEARTH and rocky.
Belbruno & Gott 2005
Valencia et al. 2006
Canup & Ward 2007
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
2. Exomoons are likely to be < MEARTH and rocky.
3. Complex life may not form on exoplanets without large
moons.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
2. Exomoons are likely to be < MEARTH and rocky.
3. Complex life may not form on exoplanets without large
moons.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection and proof of principle.
2. Exomoons are likely to be < 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
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection.
2. Exomoons are likely to be < MEARTH.
3. Complex life may not form on exoplanets without large
moons.
4. There may be more habitable exomoons than
exoplanets.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection.
2. Exomoons are likely to be < MEARTH.
3. Complex life may not form on exoplanets without large
moons.
4. There may be more habitable exomoons than
exoplanets.
3/18
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection.
2. Exomoons are likely to be < MEARTH.
3. Complex life may not form on exoplanets without large
moons.
4. There may be more habitable exomoons than
exoplanets.
Scharf 2008
3/18
Thommes et al. 2008
Molecules 2008, D. Kipping
Motivation
Detection Methods
The TDV Effect
1. A novel detection.
2. Exomoons are likely to be < 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.
3/18
Molecules 2008, D. Kipping
Motivation
•
•
•
4/18
Detection Methods
The TDV Effect
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
Motivation
•
•
•
Detection Methods
The TDV Effect
Brightness ratio  1:1010.
An Earth-sized body 0.02 micro arcseconds.
Current interferometric precision 25 micro arcseconds
(Baines et al. 2007)
NWO Proposal
4/18
Molecules 2008, D. Kipping
Motivation
•
•
•
•
Detection Methods
The TDV Effect
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
4/18
Molecules 2008, D. Kipping
Motivation
•
•
5/18
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.
Molecules 2008, D. Kipping
Motivation
•
•
5/18
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.
Molecules 2008, D. Kipping
Motivation
•
•
•
5/18
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.
=> Radial velocity cannot be used to detect exomoons.
Molecules 2008, D. Kipping
Motivation
•
6/18
Detection Methods
The TDV Effect
Could we look for the dip in star light due to an
exomoon’s shadow?
Molecules 2008, D. Kipping
Motivation
7/18
Detection Methods
The TDV Effect
Winn et al. 2008
Molecules 2008, D. Kipping
Motivation
•
Detection Methods
The TDV Effect
Planet transit + Exomoon transit
Simon et al. 2007
8/18
Molecules 2008, D. Kipping
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
8/18
Molecules 2008, D. Kipping
Motivation
•
Detection Methods
The TDV Effect
Problem 2: Average position of moon results in
lightcurves overlapping: indistinguishable.
Cabrera & Schneider 2005
8/18
Molecules 2008, D. Kipping
Motivation
•
•
9/18
Detection Methods
The TDV Effect
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
Motivation
10/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
11/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
12/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
13/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
13/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
13/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
13/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
•
•
14/18
Detection Methods
The TDV Effect
Lots of things can cause TTV, not just exomoons.
Prof. Holman called this the ‘inverse-problem’.
Molecules 2008, D. Kipping
Motivation
•
•
•
•
14/18
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 => Can’t solve!
Molecules 2008, D. Kipping
Motivation
(7/18)
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
(12/18)
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
15/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
15/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
15/18
Detection Methods
The TDV Effect
Molecules 2008, D. Kipping
Motivation
•
•
•
16/18
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.
Molecules 2008, D. Kipping
Motivation
•
17/18
Detection Methods
The TDV Effect
An Earth mass exomoon is detectable from the ground
with current instruments!
Molecules 2008, D. Kipping
Motivation
•
•
•
•
•
•
18/18
Detection Methods
The TDV Effect
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