Gullies on Mars that appear to have been carved by flowing water could instead have been created by landslides of dry powdery material, scientists have found. Troy Shinbrot and colleagues of Rutgers University in New Jersey say that Mars’s smaller gravity, which is 38% weaker than Earth’s, would allow rockfalls to last longer than they do on Earth. This means landslides could cause the kind of geological features usually only associated with running water.