Post on 27-Mar-2015
Tidal Constraints on Planetary Habitability
Rory BarnesU. of Washington
Virtual Planetary Lab
Sean N. Raymond, Brian Jackson, Richard Greenberg
Distance from Star (AU)
Mas
s of S
tar (
M)
GJ 581
Sun
Likely habitablePossibly habitable
From Selsis et al. (2007)
Distance from Star (AU)
Mas
s of S
tar (
M)
GJ 581
SunTides
Important
Distance from Star (AU)
Mas
s of S
tar (
M)
GJ 581
Sun
Tidal Locking
Prot ∞ Porb
1 + e2
≠Synchronous
Rotation!
obliquity 0
Distance from Star (AU)
Mas
s of S
tar (
M)
GJ 581
Sun
Porb = 66 de = 0.38Prot = 28 – 39 d
High e => more habitable?
No CloudsTotal cloud
coverage
Williams & Pollard (2002) + Selsis et al. (2007)
Barnes et al. (2008)
GJ 581
But tides circularize orbits…
HZ
0.2 M
semi-majoraxis
Orbit
But tides circularize orbits…
Orbital Decay -> Tidal Heating
Io has ~2 W/m2
heat flux
Such heating could be bad for life
But Some Heating is Good…
Plate tectonicsrequires
~40 mW/m2
(Williams et al. 1997)
Preventsrunaway
greenhouse
If heating > 2 W/m2
=> uninhabitable
If 0.04 < heating < 2 W/m2
=> habitable
If heating < 0.04 W/m2
=> uninhabitable(need radiogenic sources)
“Tidal Habitable Zone”
d
ce
“Super-Ios”
Super-Earth?
“Super-Ios”
Super-Mars?
or
10 M
e =
0.0
1
e =
0.5
SummaryTidal locking ≠ Synchronous rotation Rotation rates are fasterObliquities 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
ec = 0 ec = 0.01