A pre-Caloris synchronous rotation for Mercury

The planet Mercury is locked in a spin-orbit resonance where it rotates three times about its spin axis for every two orbits about the Sun. The current explanation for this unique state assumes that the initial rotation of this planet was prograde and rapid, and that tidal torques decelerated the planetary spin to this resonance. When core-mantle boundary friction is accounted for, capture into the 3/2 resonance occurs with a 26% probability, but the most probable outcome is capture into one of the higher-order resonances. Here we show that if the initial rotation of Mercury were retrograde, this planet would be captured into synchronous rotation with a 68% probability. Strong spatial variations of the impact cratering rate would have existed at this time, and these are shown to be consistent with the distribution of pre-Calorian impact basins observed by Mariner 10 and MESSENGER. Escape from this highly stable resonance is made possible by the momentum imparted by large basin-forming impact events, and capture into the 3/2 resonance occurs subsequently under favourable conditions.Comment: Nature Geosci., 201

Ischemic mitral regurgitation: Not only a bystander

Ischemic mitral regurgitation (MR) is a common complication of left ventricular (LV) dysfunction related to chronic coronary artery disease. This complex multifactorial disease involves global and regional LV remodeling, as well as dysfunction and distortion of the components of the mitral valve including the chordae, the annulus, and the leaflets. Its occurrence is associated with a poor prognosis. The suboptimal results obtained with the most commonly used surgical strategy, involving mitral valve annuloplasty with coronary bypass grafting, emphasize the need to develop alternative surgical techniques targeting the causal mechanisms of the disease. A comprehensive preoperative assessment of mitral valve configuration and LV geometry and function and an accurate quantification of MR severity at rest and during exercise may contribute to improve risk stratification and to tailor the surgical strategy according to the individual characteristics of the patient. © Springer Science+Business Media, LLC 2012.SCOPUS: ar.jinfo:eu-repo/semantics/publishe