 Scientists estimate that Phobos will be destroyed in approximately 30–50 million years, with one study's estimate being about 43 million years.Phobos' grooves were long thought to be fractures caused by the impact that formed the Stickney crater.Other modelling suggested since the 1970s support the idea that the grooves are more like "stretch marks" that occur when Phobos gets deformed by tidal forces, but in 2015 when the tidal forces were calculated and used in a new model, the stresses were too weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded by a layer of powdery regolith about thick.