However, until 2006, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole, a small region no more than about 0.5 mile wide, or 0.8 km that would set up a future impact exactly seven years later on April 13, 2036. This possibility kept it at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis' rating on the Torino scale was lowered to zero.
By 2008, the keyhole had been determined to be less than 1 km wide. During the short time when it had been of greatest concern, Apophis set the record for highest rating on the Torino scale, reaching level 4 on December 27, 2004.[10] In 2008, NASA reaffirmed the chance of Apophis impacting Earth in 2036 as being 1 in 45,000.
Thanks DoodleBob. I remember watching the Torino # reach (if memory serves) a 4, and drop back to 0, then yo-yo between zero and one, all in a short period of time (probably during one night). There was a flap about making announcements about the Torino number before everyone got everything right (which is an imaginary state, btw). :^)