Mars's gravity is tearing Phobos apart.
This landscape was sculpted by the elements, by the wind and the rain.
But on Phobos, there is no wind and rain, and so the landscape is sculpted by something else.
It's actually sculpted by gravity.
When you've got a planet and a moon orbiting around each other and spinning on their axes, very complex gravitational forces come into play.
They're called tidal forces and they act to deform the moon and also actually slightly deform the planet.
And they also act to change the orbits.
In the case of Mars and Phobos, what's changing is that Phobos is descending towards Mars in its orbit, so it's only about 6,000 kilometres above the surface now.
Ultimately, over time, Phobos gets closer to Mars, and that means the tidal forces get stronger and stronger.
The grooves on the surface are stretchmarks and fractures.
