Solar Particle Tracks in Glass from the Surveyor 3 Spacecraft

Science  26 Mar 1971:
Vol. 171, Issue 3977, pp. 1237-1239
DOI: 10.1126/science.171.3977.1237


A glass filter from Surveyor 3 has a surface density of ∼1 x 106 tracks per square centimeter from heavy solar flare particles. The variation with depth is best fitted with a solar particle spectrum dN/dE = 2.42 x 106 E-2 [in particles per square centimeter per year per steradian per (million electron volts per nucleon)], where E is the energy and N is the number of particles, from 2 million electron volts per nucleon to ∼7 million electron volts per nucleon and dN/dE = 1.17 x 107 E-3 at higher energies. Not much difference is observed between 0.5 and 5 micrometers, an indication that there is a lack of track-registering particles below 0.5 million electron volts per nucleon. The Surveyor data are compatible with track results in lunar rocks, provided an erosion rate of ∼10-7 centimeter per year is assumed for the latter. The results also suggest a small-scale erosion process in lunar rocks.