- 99942 Apophis is a near-Earth asteroid that has garnered significant scientific and public attention due to its size, close approaches to Earth, and initial potential for impact.
- Discovered on June 19, 2004, by astronomers at the Kitt Peak National Observatory in Arizona, Apophis is approximately 340 meters (1,100 feet) in diameter—large enough to cause regional devastation in the event of an impact. It is classified as an Aten-type asteroid, meaning its orbit brings it closer to the Sun than Earth’s orbit at certain points, and it crosses Earth’s path around the Sun.
- What made Apophis especially notable early on was the alarming probability of a potential collision with Earth on April 13, 2029. Initial observations led scientists to calculate a nearly 3% chance of impact, prompting intense interest from the planetary defense community. However, subsequent observations and refined orbital calculations eliminated the 2029 impact risk, as well as any possibility of a collision in 2036. Instead, Apophis will make a dramatic but safe close flyby of Earth on April 13, 2029, passing at a distance of approximately 31,000 kilometers (19,000 miles)—closer than some geostationary satellites. This encounter will be visible to the naked eye from parts of Europe, Africa, and Asia, providing a rare opportunity for direct observation of a large asteroid.
- Apophis is expected to experience gravitational effects from Earth during its 2029 flyby, which may alter its rotation and orbital trajectory slightly. These interactions provide a unique natural experiment to study the Yarkovsky effect (a force acting on a rotating body due to uneven thermal emissions) and tidal forces on small solar system bodies. Apophis’s composition is likely similar to other stony S-type asteroids, consisting of silicate rock and metal. Spectral analyses suggest it may be a rubble-pile asteroid—a loosely bound collection of rocks and dust held together by gravity—though its exact internal structure remains uncertain.
- Beyond the risk it once posed, Apophis has become a valuable object for advancing asteroid science and planetary defense efforts. NASA and other space agencies plan to observe it closely during and after the 2029 flyby using ground-based telescopes and possibly space missions. In particular, the European Space Agency’s Hera mission and NASA’s OSIRIS-APEX (a repurposed OSIRIS-REx spacecraft) may investigate Apophis more directly. These efforts will help scientists better understand asteroid dynamics, surface composition, and response to tidal forces—all essential for refining strategies to prevent future impacts.
- In summary, 99942 Apophis transitioned from a perceived threat to a scientific opportunity. Its upcoming close approach offers an unprecedented chance to study a large asteroid in detail under the influence of Earth’s gravity. As such, it has become a cornerstone in both planetary science and the field of planetary defense, reminding us of the importance of tracking and preparing for near-Earth objects that could one day pose real risks.
