tidal constraints on planetary habitability rory barnes u. of washington virtual planetary lab sean...
TRANSCRIPT
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