TRITONS STREAKS AS WINDBLOWN DUST

THE encounter of the Voyager 2 spacecraft with Neptune's satellite Triton revealed many 'dark' (about 10-20% darker than the adjacent frost) surface streaks in Triton's southern hemisphere1, resembling the streaks that are due to windblown dust on Mars2. It seems therefore that dust transport by winds in Triton's tenuous atmosphere is required, the main question being the mechanism for raising dust from the surface or sub-surface. The two obvious candidates are geyser-like eruptions and direct lofting by surface winds1. Here we show that, despite Triton's tenuous (16±3 μbar) atmosphere3, low-cohesion grains with diameters of ≲5 μm, may be carried into suspension by aeolian surface shear stress, given expected geostrophic wind speeds4 of ∼10ms-1. (The wind velocities needed to lift grains as cohesive as those found on Earth, however, are implausibly high.) For erupting plumes, we show that dust-settling timescales and expected wind velocities yield streak length scales in good agreement with those observed. Both candidate mechanisms therefore seem to be consistent with present observations of Triton. © 1990 Nature Publishing Group.