On April 13, 2029, at 21:46 UT, the near-Earth asteroid 99942 Apophis will pass approximately 32,000 kilometers above Earth’s surface — roughly 5.6 Earth radii — placing it well inside the ring of geostationary satellites that orbit the planet, geopolitika.no reported. An asteroid of this size passes this close to Earth only once every 7,500 years on average.
The close approach offers planetary scientists a rare natural laboratory while marking a turning point for planetary defense work. Although the risk of an impact in the foreseeable future has been definitively ruled out, the passage provides an unprecedented opportunity to observe how Earth’s gravity reshapes a small celestial body.
From Impact Risk to Scientific Opportunity: How Apophis Was Cleared
Apophis was discovered in June 2004 and quickly drew attention when initial orbital calculations showed a significant probability of an Earth impact in 2029. Later observations gradually reduced the estimated risk. In 2021, more precise radar measurements allowed astronomers to remove Apophis from NASA’s Sentry risk list, establishing with high confidence that an impact is excluded for at least the next hundred years.
The uncertainty in Apophis’ orbit once spanned several hundred kilometers. For the 2029 close approach, that uncertainty has been reduced to just a few kilometers.
Get ready to wave to an asteroid 👋🪨 In 2029, asteroid Apophis will swing by Earth, passing safely about 20,000 miles from the surface. The OSIRIS-APEX mission will meet up with the asteroid shortly after, to map the surface and study its chemical makeup. pic.twitter.com/SShNdmLM14
A 340-Meter Asteroid With 100 Times the Mass of Tunguska
Apophis’ physical properties illustrate the scale of the 2029 event. The irregularly shaped stony asteroid has a diameter of approximately 340 to 375 meters, an estimated mass of around 27 million tons, and a density of about 1.95 g/cm³. It rotates relatively slowly, with one rotation taking roughly 30.6 hours.
For comparison, Apophis has more than 100 times the mass of the object behind the 1908 Tunguska event and 5,000 times the mass of the meteor that exploded over Chelyabinsk in 2013.
5. The 2029 flyby is an incredibly rare event By comparing impact craters across the Solar System with the sizes and orbits of all known asteroids, scientists believe that an asteroid as large as Apophis only comes this close to Earth once every 5000 to 10 000 years.
Earth’s Gravity Will Reshape Apophis
The 2029 passage is invaluable for research because Earth’s gravity will alter Apophis in measurable ways. The primary mechanism is tidal forcing: as the asteroid passes through Earth’s gravitational field, gravity pulls differently on different parts of the body, creating powerful torques.
Researchers expect several effects:
- Orbital change: Earth’s gravity will significantly affect Apophis’ orbit around the Sun. The semi-major axis is expected to change from approximately 0.9 to 1.1 astronomical units, shifting the asteroid’s classification from an Aten-type to an Apollo-type orbit.
- Rotation state change: Tidal torques will alter how the asteroid rotates. Apophis is believed to tumble rather than rotate stably around one of its principal axes.
- Surface and structural effects: Stresses from tidal forces are expected to be strong enough to trigger seismic activity across the asteroid or surface landslides. At roughly 5.6 Earth radii, Apophis passes well within the theoretical “seismic limit” for such processes. The asteroid will not be torn apart, but the event could produce measurable surface changes on the order of centimeters to decimeters, and possibly eject dust.
What Would Happen If Apophis Hit Earth
Though the 2029 passage is harmless, researchers have evaluated impact scenarios to understand what is ruled out. If Apophis were to strike land, the impact would form a crater roughly 4.3 kilometers wide in sedimentary bedrock and flatten several thousand square kilometers, potentially killing millions in a densely populated region and triggering a brief regional impact winter, while an ocean impact could generate destructive tsunamis.
A land impact would create a crater about 4.3 kilometers in diameter in sedimentary bedrock and flatten an area of several thousand square kilometers, with potential casualties in the millions in a densely populated region. An ocean impact, statistically more likely given that water covers 70 percent of Earth’s surface, could generate devastating tsunamis; one simulation of an impact off California produced a wave 170 meters high moving at 100 km/h.
In 2029, Apophis, a ~370m asteroid, will pass just ~31,000 km from Earth. That’s ~1/10 the distance to the Moon. Inside the orbit of geostationary satellites. Visible to the naked eye. Impact risk this time is low, but the flyby could shift its future trajectory. A direct hit… pic.twitter.com/r3tHhVq9cT
NASA Proved Asteroid Deflection With DART in 2022
The best-tested technology for deflecting an asteroid is a kinetic impactor: a spacecraft that simply collides with the asteroid at very high speed. NASA tested the method with the DART mission in September 2022, when the spacecraft struck the 150-meter asteroid Dimorphos and changed its orbital period by approximately 33 minutes. The collision also produced a momentum transfer enhancement factor between 2.4 and 4.9, meaning ejected rock and dust provided two to five times the pushing effect of the spacecraft alone.
At around 340 meters in diameter, Apophis is larger than Dimorphos. Deflecting it would require more energy and greater momentum transfer, but studies suggest a single very large impactor, such as a Starship-class vehicle, could provide sufficient deflection for asteroids in the 100-to-200-meter range. For objects larger than about 500 meters, multiple impactors or higher collision velocities would be needed.
Who Decides Whether to Use Nuclear Weapons Against an Asteroid?
The question of whether a nation could destroy Apophis is misplaced. The physics of orbits and collisions shows it is far safer and more predictable to nudge an asteroid slightly off course than to shatter it. A country with proven deep-space flight technology could in principle push an object the size of Apophis off course. Exploding the asteroid into pieces would be far riskier and much harder to predict.
Astronomers Confirm Apophis’s 2029 Approach
When exactly will Apophis pass closest to Earth?
Apophis will reach its closest point on April 13, 2029, at 21:46 UT, passing about 32,000 kilometers above Earth’s surface.
Has the impact risk been completely eliminated?
Precise radar measurements in March 2021 allowed astronomers to remove Apophis from the Sentry risk list with high confidence.