In their Eos article (16 December 2003, pp. 561 & 567), Rochette et al. described their experimental investigation of the demagnetization of pyrrhotite under pressure and explored the implications for impact demagnetization on Mars. Although the experimental results are very rigorous, there are a few inaccuracies in problems with the discussion of impact demagnetization; namely, the distinction between magnetized and non-magnetized crust, the modeling of impact-induced shock pressure distribution, and the discussion of plausible martian magnetic carriers. First, the map shown in their Figure 1 is somewhat deceptive. It shows only those anomalies with amplitude > 20 nT at 400 km altitude, and the authors refer to the 20-nT contour as the limit of magnetized and non-magnetized Noachian crust. In fact, most of the Noachian age southern highlands crust is magnetized, the main exceptions being the interiors of Hellas and Argyre basins and the Tharsis region. The average intensity of magnetic anomalies as a function of radius around the Hellas, Argyre, and Isidis basins (Figure 1) shows the crust to be completely demagnetized only within ˜ 0.8 x the basin radius.