On 13 April 2029, asteroid 99942 Apophis passes just 31,600 km above Earth's surface — closer than geostationary satellites and well within the Moon's orbit. At roughly 340 metres across, Apophis is large enough that Earth's gravity will deflect its path and alter its orbit for decades afterward, a phenomenon called a gravitational keyhole effect. The encounter was once briefly rated Torino Scale 4 before refined observations ruled out an impact for at least a century. The simulation begins on 6 April 2029, when Apophis is still roughly four million kilometres away. Positions and velocities are from JPL Horizons.