Atmospheric thermal tides may prevent synchronous rotation

Leconte et al. (2015) "Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars"
http://www.sciencemag.org/content/early/2015/01/16/science.1258686.abstract

Judging by the abstract, apparently atmospheric thermal tides (invoked to explain why Venus is not tidally-locked) may also be effective at preventing spin-synchronisation of planets with thinner atmospheres, including in the HZ of low mass stars. Threshold given is ~0.5--0.7 solar mass host star, which IIRC gets you down to about M0--M1.

I saw this yesterday. Personally, I don't think "prevent" is the best word to describe it. "Reduce" or "slow down" tidal synchronization might be a better description, IMO.

PlutonianEmpire wrote:I saw this yesterday. Personally, I don't think "prevent" is the best word to describe it. "Reduce" or "slow down" tidal synchronization might be a better description, IMO.

Not really: it's a change in the value of the equilibrium rotation itself. The exact 1:1 lock is not an equilibrium rotation (let alone a stable equilibrium) in the presence of thermal tides, instead you seem to end up with 4 equilibria (2 stable, 2 unstable), none of which are exactly synchronous.

Paper on arXiv: http://arxiv.org/abs/1502.01952