Dust devils and dust storms are prevalent on Mars, which are sometimes observable by telescopes from Earth.[8] Planet-encircling dust storms (global dust storms) occur on average every 5.5 earth years on Mars[2][8] and can threaten the operation of Mars rovers.[9] However, the mechanism responsible for the development of large dust storms is still not well understood.[10][11] It has been suggested to be loosely related to gravitational influence of both moons, somewhat similar to the creation of tides on Earth.