Phobos, the inner and larger of the two moons of Mars, in a composite of photographs taken by the Viking 1 orbiter in October 1978 from a distance of about 600 km (370 miles). The most prominent feature is the impact crater Stickney, which is almost half as wide as the moon itself. Also visible are linear grooves that appear to be related to Stickney and chains of small craters.
an image of a triangle in the middle of some dirt and water with small dots on it
The Viking 1 orbiter captured this image of Phobos in 1977. The Stickney crater is on the left, and the mysterious grooves can be seen running horizontally. Image: NASA Goddard Space Flight Center.
