Nature 403, 381– 382 (2000)

In this communication, I estimated the biomass that could be supported by mixing the ice irradiation products HCHO and H2O2 into Europa's ocean, finding values that ranged from 107 g to 1010 g. However, a calculational error in the higher estimate has recently come to my attention (E. J. Gaidos, K. N. Nealson and J. L. Kirschvink, personal communication). The correct result is 108 g, making detectability of potential Europan life under this model considerably more difficult. I present a revised calculation and discuss related practical issues in the search for life on Europa at http://www.seti.org/pdf/chyba_lander.pdf.