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Tidal Constraints on Planetary Habitability Rory Barnes U. of Washington Virtual Planetary Lab Sean N. Raymond, Brian Jackson, Richard Greenberg.

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Presentation on theme: "Tidal Constraints on Planetary Habitability Rory Barnes U. of Washington Virtual Planetary Lab Sean N. Raymond, Brian Jackson, Richard Greenberg."— Presentation transcript:

1 Tidal Constraints on Planetary Habitability Rory Barnes U. of Washington Virtual Planetary Lab Sean N. Raymond, Brian Jackson, Richard Greenberg

2 Distance from Star (AU) Mass of Star (M ) GJ 581 Sun Likely habitable Possibly habitable From Selsis et al. (2007)

3 Distance from Star (AU) Mass of Star (M ) GJ 581 Sun Tides Important

4 Distance from Star (AU) Mass of Star (M ) GJ 581 Sun Tidal Locking P rot P orb 1 + e 2 Synchronous Rotation! obliquity 0

5 Distance from Star (AU) Mass of Star (M ) GJ 581 Sun P orb = 66 d e = 0.38 P rot = 28 – 39 d High e => more habitable ?

6 No Clouds Total cloud coverage Williams & Pollard (2002) + Selsis et al. (2007) Barnes et al. (2008) GJ 581

7 But tides circularize orbits… HZ 0.2 M semi- major axis Orbit

8 But tides circularize orbits…

9 Orbital Decay -> Tidal Heating Io has ~2 W/m 2 heat flux Such heating could be bad for life

10 But Some Heating is Good… Plate tectonics requires ~40 mW/m 2 (Williams et al. 1997) Prevents runaway greenhouse

11 If heating > 2 W/m 2 => uninhabitable If 0.04 < heating < 2 W/m 2 => habitable If heating < 0.04 W/m 2 => uninhabitable (need radiogenic sources)

12 Tidal Habitable Zone

13 d c e

14 Super- Ios Super- Earth?

15 Super- Ios Super- Mars? or

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17 10 M e = 0.01 e = 0.5

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20 Summary Tidal locking Synchronous rotation Rotation rates are faster Obliquities go to zero Tides may remove planets from HZ Tidal heating may be severe (super-Io) But tidal heating may drive plate tec. Tidal Habitable Zone First-detected rocky planets in HZ will be affected by tides

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22 e c = 0 e c = 0.01


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