Letter from Thomas Gold to Dr M Nussinov, Space Research Institute, USSR Academy of Sciences, 88 Profsojuznaja St., 117485, Moscow, USSR Regrets that they have not done any more than described in their article in the field of laser simulation of hypervelocity impacts. Gold believes the technique is valuable, and he would be glad to hear of any progress Nussinov may make with it. There is one observation that they have that suggests that extremely thin glass bubbles form and freeze in both laser simulation and real micrometeorite impacts. If Nussinov has any observations of this phenomenon Gold would be glad to hear of them. 1 February 1974