It is important to keep in mind that Fig. 10 does not include the large spike at zero warning time due to the undiscovered objects. For example, Fig. 8 shows that 60% of 200 m diameter objects remain undiscovered at the end of the four years of PS1 surveying. Thus, the most probable awareness (warning) time for the smaller objects is zero. But when they are discovered before the apparition in which they impact the warning time can be many decades. As discussed above, to be 90% effective at eliminating the risk of an unanticipated impact in the next 100 years for objects >140 m diameter requires a PS1-like system to surveymuchlonger or a more powerful system like PS4 (Kaiser and Pan-STARRS Team, 2005) or the system being developed by the LSSTC (Ivezic´ et al., 2007).