Phobos, the 22-km diameter innermost moon of Mars, is a groovy body. Unlike its little brother Deimos, Phobos has developed a striking pattern of parallel linear features running across its surface. These grooves are a distinctive global feature of Phobos, not present on Deimos. How they formed has perplexed planetary geologists for over forty years, since they were first imaged in geologic detail by NASA’s Viking missions.
Click here for original story, Phobos surface striations tell a story of its rupturing interior
Source: Phys.org