Apophis

Apophis (99942 Apophis) is a near-Earth asteroid roughly 370 meters (0.37 km) in diameter, classified as an Aten-type asteroid with an orbit that crosses Earth's. Discovered in 2004, it initially caused worldwide alarm when preliminary calculations gave it a 2.7% chance of striking Earth in 2029 — the highest impact probability ever assigned to an asteroid. Subsequent observations eliminated the impact risk, but confirmed that on April 13, 2029, Apophis will pass just 31,000 km from Earth's surface — closer than geostationary satellites and easily visible to the naked eye from parts of Europe, Africa, and Asia. It is an Sq-type asteroid composed of silicates with some metal content.

Apophis is normally very faint at magnitude 19–22, far beyond visual range. However, during its historic close approach on April 13, 2029, it will brighten to about magnitude 3.1 — easily visible to the naked eye as a fast-moving point of light crossing the sky. From Europe and Africa, observers will be able to watch it move noticeably against the star background in real time. Before and after the close approach, it may be visible in large amateur telescopes (12 inches or more) for several weeks. This will be an unprecedented event — the first time a potentially hazardous asteroid of this size will be visible to the unaided eye.

Apophis was discovered on June 19, 2004 by Roy Tucker, David Tholen, and Fabrizio Bernardi at Kitt Peak National Observatory. Initial orbit calculations in December 2004 gave a startling 2.7% impact probability for April 13, 2029, briefly raising it to Level 4 on the Torino Impact Hazard Scale — the highest level ever assigned to any asteroid. Additional observations progressively reduced the risk, and by 2021, radar observations from Goldstone completely ruled out any impact for at least 100 years. The asteroid was named after Apophis (Apep), the Egyptian serpent god of chaos and destruction.