Swiss cheese features

[1] They are typically a few hundred meters across and 8 metres deep, with a flat base and steep sides.

They tend to have similar bean-like shapes with a cusp pointing towards the south pole, indicating that insolation is involved in their formation.

Near the Martian summer solstice, the Sun can remain continuously just above the horizon; as a result the walls of a round depression will receive more intense sunlight, and sublimate much more rapidly than the floor.

[2][3] As the seasonal frost disappears, the pit walls appear to darken considerably relative to the surrounding terrain.

The halo's appearance correlates to the global dust storm that began earlier in the same Martian year.