When asteroid 99942 Apophis was discovered in June 2004, early calculations indicated a 2.7 percent chance of impact on April 13, 2029. That brief probability spike earned it a rating of 4 on the Torino Scale, the highest level ever reached by a known celestial object.
Subsequent observations quickly ruled out the 2029 collision. However, scientists remained concerned about the 2036 and 2068 encounters because Earth gravitational perturbation during the 2029 flyby could send Apophis through an orbital "keyhole", a narrow region of space that would align its orbit for an impact on a future return.
In March 2021, Apophis made a distant flyby 17 million kilometers from Earth. Astronomers at NASA Goldstone Deep Space Communications Complex in California paired with the 100-meter Green Bank Telescope in West Virginia to conduct high-precision radar imaging.
The radar data pinned down Apophis distance to within 150 meters and its velocity to a fraction of a millimeter per second. With these measurements, dynamicists calculated Apophis orbit out past the year 2121. The results completely excluded any impact risk in 2029, 2036, and 2068.
Following the radar analysis, NASA CNEOS officially removed Apophis from the Sentry Risk Table on March 25, 2021. When it passes Earth on Friday, April 13, 2029, it will safely cruise 31,600 kilometers above our surface, closer than geostationary weather satellites and easily visible to the naked eye across Europe, Africa, and parts of Asia.