The inward spiral of Phobos sets the stage for two possible outcomes: catastrophic breakup or a dramatic surface impact. This breakup could occur in as little as 20 to 40 million years, and its result would be a ring of debris encircling Mars. However, if Phobos maintains enough cohesion during its descent, denser fragments may survive the breakup and eventually crash into Mars. These impacts would be relatively slow and shallow but still capable of carving visible craters into the surface of Mars. Once Phobos reaches an altitude of 3,400 miles from the surface of Mars, it will cross the threshold of the Roche limit.