On the evening of April 13, 2029, a chunk of rock roughly 1,100 feet across will streak past Earth closer than the ring of satellites that deliver television signals and weather data to much of the planet. Asteroid 99942 Apophis will skim within about 19,800 miles of the surface, according to NASA, making it the nearest known flyby by an asteroid of this size in recorded history. There is no risk of impact. What there is, scientists say, is an extraordinary chance to study a potentially hazardous space rock at point-blank range and to stress-test the planetary defense systems that would matter if a future asteroid were not so cooperative.
How close is close?
Apophis will pass inside the belt of geostationary satellites, which orbit at roughly 22,236 miles above the equator. NASA’s Jet Propulsion Laboratory places the closest approach at about 31,600 km (19,600 miles) from Earth’s surface, a figure refined through radar observations taken during the asteroid’s 2020 and 2021 flybys. For perspective, the Moon sits about 238,900 miles away. Apophis will be roughly 12 times closer than the Moon, near enough that observers in parts of Europe, Africa, and western Asia should be able to spot it with the naked eye as a fast-moving point of light.
Different NASA pages round the distance slightly differently, some citing “approximately 20,000 miles” and others giving a more precise geometric figure measured from Earth’s center rather than its surface. The variation reflects rounding conventions, not scientific disagreement. Every current analysis converges on the same conclusion: Apophis will pass strikingly close but will miss.
A brief history of alarm and relief
When astronomers at the Kitt Peak National Observatory discovered Apophis in June 2004, early orbit calculations briefly suggested a 2.7 percent chance of an Earth impact in 2029. The asteroid was assigned a rating of 4 on the Torino Scale, a measure of impact hazard. No other known asteroid has ever scored that high. The finding triggered urgent follow-up observations worldwide.
Within months, additional tracking data shrank the uncertainty in Apophis’s orbit and eliminated the 2029 impact scenario. Later radar campaigns, documented by JPL’s Center for Near-Earth Object Studies, progressively ruled out impact possibilities for subsequent close approaches as well. By March 2021, high-precision radar measurements from Goldstone allowed JPL to declare that Earth is safe from Apophis for at least 100 years. The asteroid that once topped the global threat list is now, for practical purposes, off it.
What scientists plan to learn
NASA has a spacecraft already en route. The agency repurposed its OSIRIS-REx probe, which successfully returned a sample from asteroid Bennu in September 2023, and renamed the extended mission OSIRIS-APEX (Apophis Explorer). The spacecraft is scheduled to rendezvous with Apophis shortly after the 2029 flyby and spend roughly 18 months studying it up close, according to NASA’s mission overview.
The timing is deliberate. As Apophis swings past Earth, our planet’s gravity will tug on the asteroid hard enough to potentially reshape its surface. Loose rocks and dust could shift. Landslides might expose fresh subsurface material. The asteroid’s 30.6-hour rotation could speed up or slow down. If any of those changes occur, OSIRIS-APEX would capture the first direct evidence of gravitational disruption on a small body, data that could reshape the models used to plan future deflection missions like NASA’s DART program, which successfully altered the orbit of asteroid Dimorphos in 2022.
Ground-based observatories will also mount coordinated campaigns. Radar facilities at Goldstone and Arecibo’s successor instruments, along with infrared and optical telescopes worldwide, plan to track Apophis before, during, and after closest approach. The goal is to compare the asteroid’s shape, spin, and surface properties on either side of the encounter, building a before-and-after portrait at a level of detail never achieved for a passing asteroid.
What a strike would mean, and why it won’t happen
Apophis is classified as an S-type (stony) asteroid with an estimated diameter between 340 and 390 meters, based on infrared measurements from NASA’s NEOWISE mission and thermal modeling using data from the Gran Telescopio Canarias and the Herschel Space Observatory. An object that size striking Earth would release energy far exceeding any nuclear weapon ever detonated, enough to devastate a region the size of a small country or, in the case of an ocean impact, generate significant tsunamis. The U.S. Geological Survey has published analyses examining the cascading hazards of such an event, including blast waves, thermal radiation, and secondary seismic effects.
None of that will happen in 2029 or anytime in the foreseeable future. JPL’s orbit solution, built on decades of optical and radar tracking, constrains Apophis’s path tightly enough to rule out passage through any known “gravitational keyhole,” a narrow corridor in space that, if crossed during a flyby, could bend an asteroid’s orbit toward a future collision. As of April 2026, no such keyhole scenario exists for Apophis.
Open questions heading into 2029
Several unknowns remain. Chief among them is Apophis’s internal structure. Observations so far cannot definitively determine whether the asteroid is a solid monolith or a loosely bound “rubble pile” held together mainly by gravity. The distinction matters for planetary defense: a porous body absorbs the momentum of a kinetic impactor differently than solid rock, which changes how much force would be needed to nudge it off course. Close-up measurements from OSIRIS-APEX, combined with analysis of how the asteroid responds to Earth’s tidal forces, could finally settle the question.
The post-flyby orbit also warrants continued monitoring. Earth’s gravity will bend Apophis’s path, shifting it from an Aten-class orbit (mostly inside Earth’s orbit) to an Apollo-class orbit (crossing Earth’s orbit from the outside). While the new trajectory has been modeled extensively, small measurement uncertainties compound over decades. Ongoing radar tracking after 2029 will be needed to keep long-range predictions sharp.
Visibility during the flyby itself is another practical concern. Apophis will cross the sky quickly, and its brightness and orientation will change as it recedes. Weather, local time zones, and horizon conditions will determine who gets a clear view. Professional campaigns are still finalizing which instruments and wavelengths will yield the best data during the brief window of closest approach.
A rehearsal Earth actually needs
Beyond the science, the 2029 flyby functions as a full-scale rehearsal for planetary defense. The same telescopes, radar arrays, spacecraft, and international coordination networks being mobilized for Apophis would be critical if a different asteroid were ever found on a collision course. Every protocol exercised during this encounter, from rapid orbit determination to public communication, builds institutional muscle for a scenario that, statistically, will eventually arise.
For now, Apophis is a gift: a large, well-tracked asteroid arriving on a predictable schedule, close enough to study in extraordinary detail, and certain to miss. The three years between now and April 2029 give researchers time to prepare instruments, refine models, and coordinate across agencies and borders. When the asteroid finally appears in the evening sky over the Eastern Hemisphere, it will be the closest many people ever come to seeing a world-altering threat pass harmlessly by, and the closest science has ever come to watching one up close.
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*This article was researched with the help of AI, with human editors creating the final content.
