The tiny Martian moon Phobos orbits the Red Planet in this animation of images from the Hubble Space Telescope. Please click the animation to enlarge it. (Source: NASA, ESA, and Z. Levay (STScI) On May 12, 2016, when Mars was 50 million miles from Earth, the Hubble Space Telescope turned its incredibly sharp eye toward the Red Planet. The time-lapse animation above reveals what it saw. That little white speck zinging around Mars is Phobos, a football-shaped moon just 16.5 miles by 13.5 miles by 11 miles. You're seeing it in an animation consisting of 13 separate exposures by Hubble. Phobos looks like it is speeding along at an unbelievably rapid clip. In reality, Hubble acquired the 13 frames over the course of 22 minutes. So things are really sped up in the time-lapse. Even so, Phobos is something of a sprinter. As NASA puts it:
The little moon completes an orbit in just 7 hours and 39 minutes, which is faster than Mars rotates. Rising in the Martian west, it runs three laps around the Red Planet in the course of one Martian day, which is about 24 hours and 40 minutes. It is the only natural satellite in the solar system that circles its planet in a time shorter than the parent planet's day.
And this is pretty cool too:
Orbiting 3,700 miles above the Martian surface, Phobos is closer to its parent planet than any other moon in the solar system. Despite its proximity, observers on Mars would see Phobos at just one-third the width of the full moon as seen from Earth. Conversely, someone standing on Phobos would see Mars dominating the horizon, enveloping a quarter of the sky.
https://www.youtube.com/watch?v=J7Cumuf_5CY For more on Phobos photobombing Hubble's observations of Mars, as well as information about the moon, missions that have observed it, and much more, check out the video above from NASA.