  We point out that time-dependent CP asymmetries in B_s to K^{*0} \bar K^{*0}
decays probe the presence of new physics in b to s transitions with an
unprecedented theoretical accuracy. We show that, contrary to the case of B_d
to phi K_S, it is possible to obtain a model-independent prediction for the
coefficient S(B_s to K^{*0} \bar K^{*0}) in the Standard Model. We give an
estimate of the experimental precision achievable with the next generation of B
physics experiments. We also discuss how this approach can be extended to the
case of B_s to \bar K^{*0} K^0, B_s to K^{*0} \bar K^0 and B_s to K^0 \bar K^0
decays and the different experimental challenges for these channels.
