Observed Changes at Viking Lander 1

A local dust storm raged in Chryse Planitia, Mars, in June 1981. The changes wrought in the vicinity of the lander (Mutch Memorial Station) by this storm sometime near Sol 1742 were partly described previously. Here, changes related to the storm are itemized, evidence for wind directions during the peak of the storm are cited, and two observations unrelated to the storm are noted. The observations suggest that the eroding winds of the Sol 1742 storm were more easterly (N. 35 deg to 90 deg E.) than those (N. 5 deg to 11 deg E.) that formed the large wind tails; and fragments in erosional residues are 0.7 cm and larger, but smaller ones may be present. Some fragments 0.4 to 0.5 cm and smaller were somehow removed, at least locally; wind speeds of the 1742 local storm were probably greater than those of a previous local dust storm (25 to 30 m/s) that occurred during the same season on Sol 423 because the earlier storm did not alter the surface; the major, if not entire, amount of erosion by the storm occurred between Sols 1728 and 1757; and erosion chiefly occurred where the surface configuration and material properties were altered by the lander and its sampler.