It appears to be tidal: http://www.blastr.com/2017-5-8/no-we-havent-found-signs-life-alien-or-otherwise-solar-system http://www.blastr.com/2017-5-8/no-we-havent

It appears to be tidal: http://www.blastr.com/2017-5-8/no-we-havent-found-signs-life-alien-or-otherwise-solar-system http://www.blastr.com/2017-5-8/no-we-havent-found-signs-life... (link to bad astronomy, a reasonably good explainer type source)