99942 Apophis

DESCRIPTION

99942 Apophis is an elongated stony asteroid about 340 meters across — roughly the height of the Eiffel Tower. It was discovered on 19 June 2004 from Kitt Peak, Arizona, observed for two nights, and lost. When it was recovered that December, the orbit solutions converged on something no astronomer had seen before: a measurable chance of striking Earth, on Friday the 13th of April, 2029. The discoverers named it for Apep — Apophis, in Greek — the Egyptian serpent of chaos who attacked the sun god nightly. Two of them were, reportedly, also fans of the Stargate villain who borrows the name.

The impact never firmed up. The close approach did. On 13 April 2029, Apophis will pass about 32,000 kilometers above Earth's surface — inside the ring of geosynchronous satellites at 35,786 kilometers. CNEOS estimates a pass this close by an object this large occurs about once in 800 years. It will be visible to the naked eye from Europe, Africa, and western Asia: a point of light crossing the evening sky. This file exists because Apophis once held the highest impact rating ever assigned to an asteroid — and because of what two decades of measurement did to that number.

THE RECORD

• 19 Jun 2004 — Discovered by Tucker, Tholen, and Bernardi (Kitt Peak). Lost after two nights.
• 18 Dec 2004 — Recovered.
• 24–27 Dec 2004 — Computed impact probability for 13 April 2029 peaks at 2.7 percent (about 1 in 37). Torino Scale 4: the highest rating ever assigned, still the record.
• 27 Dec 2004 — Precovery images from March 2004 extend the observation arc. The 2029 impact is ruled out within days of being announced.
• Jan 2005 — Arecibo radar cuts orbital uncertainty by roughly 98 percent. Concern shifts to a possible 2036 "keyhole" passage.
• Jan 2013 — Goldstone and Arecibo radar rule out 2036; odds below one in a million.
• Feb–Mar 2021 — Goldstone and Green Bank track Apophis by radar to about 150 meters' accuracy at 17 million kilometers. Sentry's removal record for 99942 is logged 21 February 2021; on 25 March 2021 NASA announces no impact risk for at least 100 years. ESA's risk list follows the same week.
• 1 Jul 2026 — Verified for this file: the Sentry API returns "specified object removed" for 99942. Apophis is not on the risk table.
• Ahead — ESA's Ramses, funded in full at the November 2025 Ministerial, launches April 2028 to reach Apophis by February 2029 and observe the flyby from alongside; NASA's OSIRIS-APEX arrives weeks after. Ground telescopes reacquire the asteroid in 2027.

THE HONEST READ

A 340-meter impact would be a regional catastrophe, not an extinction — and none is scheduled. For 2029 to go differently, something unobserved would have to shove the asteroid: a 2024 study put the odds of an unseen small-asteroid strike deflecting it onto a collision course below one in two billion, and routine observations from 2027 will retire even that. This is the archive's flagship case for the method — four days at 2.7 percent in 2004, then twenty years of radar grinding the number to zero. The Watch expects a bright point of light over the Eastern Hemisphere on a Friday evening, two spacecraft flying alongside, and nothing else.

— The Archivist