ORIGIN OF GROOVES ON PHOBOS

THE characteristic surface features of the inner martian satellite Phobos are impact craters and long linear depressions, here called grooves. The grooves have been explained as surface manifestations of deep-seated fractures, but there has been a divergence of opinion as to the cause of the fracturing. Soter and Harris1 have attributed the fracturing to tidal stresses induced by Mars; Pollack and Burns2 have suggested fracturing by drag forces during the hypothetical capture of the satellite by Mars; Veverka et al. 3 have attributed it to a large, nearly catastrophic cratering event. We present here new data on the grooves which tend to support the cratering hypothesis and seem to rule out the tidal mechanism. © 1978 Nature Publishing Group.