The clear double vortex at the pole of Venus is caused by the flow of energy from the sun as it interfaces with the planet's own magnetic field.

The vortical shape is always an infinite logarithmic spiral because this allows for endless and infinite energy transfer between all different things: galaxies-stars-planets-moons or a grain of sand on Miami Beach.

A picture is worth a thousand words and a visualization is even more handy, so here's an animation to show the flows of energy involved and how it works.

VISUALIZATION

You see this double vortex on Venus:

Source: ESA.int

And yet it is also visible to a lesser degree on Mars north pole as well:

Source: Astrosurf.org

This type of vortical structure will be found on almost all planets we eventually encounter and will simply be more obvious on the planets nearest the sun or which have a particulary strong solar/planetary interface. Whenever energy moves faster its vortical shape and flow becomes much more clear. Such as the vortical turbulence created by jets, the flow of a hurricane, the interaction of a planet and its sun or even the massive rotation of a galaxy.

It's fun to watch as we slowly discover all these vortical structures all over the universe.

;-)