Dune field

Very few features that point to dune fields have been found on Venus so far. Yet Venus is much drier than Earth, Mars or Titan, where dunes are common.

There are only two places on Venus where the pattern on radar images suggests a dune field. The plates show them. The faint streaks, barely visible at 100 m resolution, suggest that these places hold longitudinal (linear) dunes. The data, however, show slopes gentler than those of an actively migrating lee side. So these dunes are probably not active – if they are dunes at all (Greeley et al. 1997).

The two dune fields together cover 18,000 km² of Venus. This is only 0.004% of the surface. On Earth, by contrast, windblown sand forms cover 1.5% of the surface, on Mars 0.7% and on Titan 17%.

Why have dunes been found in so few places? Many ideas have been put forward. One is that the wind is not strong enough, except for the shock wave of an impact (Schultz 1992). The other main argument is that the surface of Venus offers too little opportunity for sand to form. Weathering is very slow and weak there. Even if sand grains did form, the high temperature would quickly turn them back into rock, for example by fusing them together.

The material of the dune field on the second plate seems to come from the complex (outflow) channel that starts at the crater Aglaonice (Greeley et al. 1995).

Wind streaks, on the other hand, are common on the surface (Greeley et al. 1997).

Kreslavsky and Bondarenko (2017) argue that none of these objections holds. There is enough wind and enough sand to make dunes. In their view, the resolution of our data is simply too low. Most of the surface of Venus shows weak anisotropy: sand is almost everywhere.

Dune fields are named with the Latin descriptor term Unda (wave).