An Apophis, a large, potentially hazardous asteroid, caused a brief period of concern in December 2004.

To test its operational readiness, more than 100 astronomers from 18 countries, including Dr. David Polishook of Israel’s Weizmann Institute’s Physics Faculty, and director of the Institute’s Observatory, participated in a planetary defense exercise in which Apophis was “deleted” from the databases so that it could be “rediscovered” by the observatories and assess its threat.