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.

When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works. Crisscrossed grooves and chains of small craters cover the Martian moon Phobos. Astronomers have ...