 Nonetheless, in November 2018, astronomers concluded that the many grooves on Phobos were caused by boulders, ejected from the asteroid impact that created Stickney crater, that rolled around on the surface of the moon.Faint dust rings produced by Phobos and Deimos have long been predicted but attempts to observe these rings have, to date, failed.Recent images from "Mars Global Surveyor" indicate that Phobos is covered with a layer of fine-grained regolith at least 100 meters thick; it is hypothesized to have been created by impacts from other bodies, but it is not known how the material stuck to an object with almost no gravity.