  We address numerically the deformation and fragmentation dynamics of a single
liquid drop subject to impulsive acceleration by a unidirectional gas stream.
The density ratio between the liquid and gaseous phases is varied in the
$10-2000$ range and comparisons are made with recent drop breakup experiments.
We show for low Ohnesorge numbers that the liquid-gas density contrast
significantly modifies the critical Weber number for the transition between
bursting and stripping fragmentation regimes, on the one hand, and for drop
fragmentation, on the other hand. We suggest a simple theoretical argument to
predict the transitional Weber number as a function of the density contrast and
show that the stabilising influence of small contrasts can be explained by
inertial effects in the nonlinear coupling between drop stretching and centroid
acceleration.
