In the News and Views Feature “Galileo at Jupiter — meetings with remarkable moons” by William B. McKinnon (Nature 390, 23–26; 1997), the heat flow from Io was given as 2.5 mW m−2. It is actually 2.5 W m−2, to compare with a terrestrial average of 90 mW m−2 (Pollack, H. N., Hurter, S. J. & Johnson, J. R. Rev. Geophys. 31, 267- 280; 1993). ‘Size’ in Table 1 refers to radius.