Complex sentence: On 24 December 2004, minor planet 99942 Apophis (at the time known by its provisional designation) was assigned a 4 on the Torino scale, the highest rating ever achieved, as there was a 2.7% chance of Earth impact on 13 April 2029.
Split into simpler sentences: On 24 December 2004, minor planet 99942 Apophis (at the time known by its provisional designation) was assigned a 4 on the Torino scale, the highest rating ever achieved. There was a 2.7% chance of Earth impact on 13 April 2029.