When an asteroid or a comet has just been discovered, its orbit is weakly constrained by the available astrometric observations and it might be the case that an impact on the Earth in the near future (within the next 100 years) cannot be excluded. If additional observations are obtained, the uncertainty of the orbit decreases and the impact may become incompatible with the available information. Thus, if we are aware that an impact is possible, it is enough to spread this information to the astronomers to convince them to follow up the object. On the contrary if this piece of information is not available, or is made available when the asteroid has been lost, the impact risk will remain until the same asteroid is accidentally recovered. This might occur too late for any mitigation action.

This problem can be solved if all the asteroids/comets, immediately after being discovered and before they can be lost, are “scanned” for possible impacts in the near future. If impacts are possible, this information has to be broadcast to the astronomers. This is the goal of impact monitoring.

It is somewhat surprising that this was not really possible until late 1999, when the first impact monitoring system, the CLOMON software robot of the University of Pisa, became operational.