The 2029 flyby of the Near-Earth Object (NEO) designated Apophis is an event of unparalleled public and scientific interest. This particular space rock has attracted significant attention since its discovery, primarily due to its initial classification as a potential impact threat. Apophis will offer a rare, safe, and highly visible demonstration of celestial mechanics as it grazes our planet. The event is anticipated with excitement, providing an opportunity for both professional astronomers and backyard observers. This article details the object, its precise path, what the public can expect to see, and the unique scientific research opportunities this close encounter will enable.
The Asteroid Known as Apophis
The official designation is 99942 Apophis, named after the ancient Egyptian god associated with chaos and darkness, a nod to the initial concern it caused. Apophis was discovered on June 19, 2004, at the Kitt Peak National Observatory in Arizona. It is classified as an S-type, or stony, asteroid, meaning its composition is rich in silicates and nickel-iron.
The asteroid has a mean diameter of approximately 340 to 370 meters, with its longest axis stretching up to 450 meters. Initial tracking suggested a small but non-zero chance of collision with Earth in 2029, a probability that briefly earned it the highest-ever rating on the Torino Impact Hazard Scale: Level 4. Subsequent, more precise observations definitively ruled out any chance of an impact for over a century, reducing its classification to Torino Scale 0.
The Trajectory and Timing of the Close Approach
The closest approach will occur on Friday, April 13, 2029. At its nearest point, Apophis will pass approximately 32,000 kilometers above Earth’s surface. This distance is less than a tenth of the distance to the Moon and is significantly closer than the orbits of many geosynchronous communications satellites.
Apophis will approach from the direction of the Sun, briefly entering Earth’s shadow before reappearing in the night sky over the Eastern Hemisphere. Its path will trace a rapid arc across the sky, becoming visible first over the Atlantic Ocean, then passing directly over Africa, and eventually receding over Asia. The trajectory is precisely known, ensuring the asteroid will safely miss the gravitational “keyhole.” Had the asteroid passed through this small, 800-meter-wide area, Earth’s gravity would have nudged its path enough to guarantee an impact seven years later in 2036.
Observing Apophis: What You Will See
Apophis will be easily visible to the unaided eye for a short period. At its brightest, the asteroid is expected to reach a visual magnitude of about 3.1, comparable to the fainter stars in the Little Dipper constellation. This brightness means that billions of people across Europe, Africa, and Western Asia, the regions beneath the pass, will have a chance to see the object.
Unlike planets or distant stars, Apophis will appear as a fast-moving, star-like point of light. The speed of its apparent movement will be striking, covering more than one degree of the sky—or about two Moon diameters—every minute. This rapid movement makes it distinct from a typical satellite or airplane, which move much more slowly across the background stars.
The peak viewing window will be relatively short, lasting only a few minutes as the asteroid streaks across the sky. While the naked eye will detect its motion, using a pair of binoculars will enhance the view, allowing observers to track the fast-moving point of light with more precision. The best hours for observation will be in the late evening, as the asteroid makes its closest pass and is high in the sky over the Eastern Hemisphere.
A Unique Opportunity for Planetary Science
The 2029 flyby provides a natural laboratory to study a large asteroid up close without the expense of a deep-space mission. Scientists will use ground-based radar facilities, such as those at Goldstone, to obtain high-resolution images of the asteroid’s surface. These radar images are expected to provide details down to the meter scale, allowing researchers to map the asteroid’s shape and surface features.
The close encounter will allow for precise measurements of the asteroid’s physical properties, including its density and internal structure. Earth’s gravity will exert tidal forces on Apophis, potentially causing quakes or landslides on its surface and altering its rotation. By observing these changes, scientists can gain insight into whether Apophis is a solid rock or a “rubble pile” of loosely held material.
The close pass will significantly alter the asteroid’s orbit, shifting its classification from an Aten-class to an Apollo-class asteroid. NASA’s OSIRIS-APEX spacecraft, redirected after its mission to Bennu, is scheduled to rendezvous with Apophis shortly after the flyby. This mission will allow the spacecraft to study the immediate effects of the Earth’s gravitational encounter on the asteroid’s surface and environment.