ELECTRICAL-DISCHARGE HEATING OF CHONDRULES IN THE SOLAR NEBULA

We present a rudimentary theoretical assessment of electrical discharg e heating as a candidate mechanism for the formation of chondrules in the solar nebula. The discharge model combines estimates of the proper ties of the nebula, a mechanism for terrestrial thunderstorm electrifi cation, and some fundamental electrical properties of gases. Large unc ertainties in the model inputs limit these calculations to order-of-ma gnitude accuracy. Despite the uncertainty, it is possible to estimate an upper limit to the efficiency of nebular discharges at melting mill imeter-sized stony objects. We find that electrical arcs analogous to terrestrial lightning could have occurred in the nebula, but that unde r most conditions these discharges probably could not have melted chon drules. Reasons for this conclusion include: (1) at gas pressures typi cal of the solar nebula, kilometer-scale electrical discharges lack en ergy flux densities high enough to melt millimeter-sized stony bodies; (2) even assuming the most favorable possible conditions, most probab le nebular discharges do not contain enough energy to ionize their own channels; (3) electrical discharge heating appears to mandate size-de pendent heating effects, which have not been observed among meteoritic chondrules; and (4) the long duration of nebular discharges requires unrealistically slow drift velocities if the particles are to remain i n the flux channel long enough to melt. Despite these difficulties, we believe the topic worthy of further investigation and suggest some ex periments which could improve our understanding of nebular discharges. (C) 1995 Academic Press, Inc.