Apophis 2029: What Would Happen if It Struck Earth?

On April 13, 2029, Earth will witness a truly extraordinary cosmic event: the close flyby of asteroid 99942 Apophis. On that day – a Friday the 13th, no less – this 340-meter-wide space rock will skim past our planet at a distance of only about 30,600 km above Earth’s surface. In astronomical terms, that is a hair’s breadth away – roughly one-tenth the distance to the Moon, and even closer than the ring of geostationary satellites that orbit Earth. Never in recorded history has an asteroid of this size come so close without impact. For scientists and skywatchers, Apophis’s flyby offers a once-in-a-thousand-years opportunity to observe a large asteroid at close range. Importantly, Apophis will not hit Earth in 2029 – NASA’s precision tracking has ruled out any impact for at least the next century. Instead, it will race past us, providing a breathtaking show and valuable scientific insights, all while leaving our planet unharmed.

As Apophis approaches on the appointed night, it will become visible to the naked eye in some regions, heralding its presence like a bright moving star. During the close approach, Apophis is predicted to shine at about magnitude 3.1 – bright enough to be seen without a telescope under dark skies. Observers across Europe, Africa, and western Asia will be favored with the view, watching as this pinpoint of light sweeps rapidly across the heavens. In fact, at peak, the asteroid will move perceptibly fast, covering an astonishing 42 degrees of sky per hour – about the width of eight full moons every minute. Over the course of that day, Apophis will trace a long arcing path: racing northwest through the constellations of Centaurus to Perseus, then curving southwest into Pisces, covering over 200 degrees of sky. To the naked eye it will appear as a fast-drifting star, a visitor from deep space hurtling past our world. As it speeds by, Earth’s gravity will tug on Apophis and subtly alter its trajectory and speed, bending its path and changing its orbital period. This gravitational interaction will be so strong that it actually shifts Apophis from one type of orbit to another (from an Aten-class to an Apollo-class orbit) going forward – a vivid demonstration of how a close planetary encounter can reshape an asteroid’s journey around the Sun. For one night, people on Earth will be able to watch with the unaided eye as a half-mile-wide asteroid glides silently among the stars, an awe-inspiring reminder of our planet’s place in a dynamic and occasionally dangerous cosmos.

When Apophis swings by Earth in 2029, it will set a record for a known asteroid of its size, coming closer than any in living memory. The spectacle has been highly anticipated since 2004, when astronomers discovered Apophis and realized just how near it would come. Early on, there were a few tense days of uncertainty – initial calculations even gave a small chance of an impact in 2029, briefly raising Apophis to a worrying level 4 on the Torino hazard scale. However, additional observations quickly refined its orbit and ruled out a collision. Now, with the approach imminent, the tone has shifted from concern to excitement. Never before will humanity have such a close look at a sizable asteroid without needing a spacecraft. Researchers are eager to study Apophis’s composition, shape, and spin as it passes by. Telescopes will monitor how Earth’s tidal forces might stir the asteroid, perhaps even causing minor “asteroid-quakes” or landslides on its surface as our planet’s gravity tugs on it. For the public, the 2029 flyby will be a planetary moment – millions stepping outside to gaze up at an ancient piece of solar system debris speeding past. It’s a vivid event that underscores both the majesty of the cosmos and the vigilance of modern science: we can not only predict such an encounter decades in advance, but also relish it as a chance to learn and marvel, secure in the knowledge that this one will pass us by safely.

Apophis will miss Earth in 2029, but what if it didn’t? Imagining the hypothetical scenario of an Apophis impact reveals just how catastrophic a large asteroid strike would be (and emphasizes why scientists were initially alarmed by this object). Apophis is about 340–370 m and is a titan of a rock hurtling at tens of thousands of kilometers per hour. Were it to collide with Earth, the energy released would be almost unimaginable: on the order of 10^19 joules, which is equivalent to more than 1,000 megatons of TNT exploding at once. In other words, an Apophis impact would unleash energy comparable to the world’s entire nuclear arsenal detonating in a single burst. This is about 100,000 times more powerful than the 2013 Chelyabinsk meteor airburst and roughly 100 times the energy of the 1908 Tunguska event in Siberia. The Tunguska impactor, only ~50–60 meters wide, flattened 80 million trees over 2,150 square kilometers in 1908 with a ~15-megaton blast. An Apophis-sized impact would be far more devastating – though, to be clear, still much smaller than the dinosaur-ending impact 66 million years ago. (The asteroid that excavated the 180-km Chicxulub crater was on the order of 10 kilometers wide and released an astonishing 100 teratons of TNT – some 100 million megatons, literally a billion times more energetic than a Hiroshima bomb. Apophis is nowhere near that scale.)

If Apophis were to strike land, the immediate effects would be utterly devastating. The asteroid would punch through the atmosphere at hypersonic speed and strike the ground with such force that it would excavate a crater several kilometers across – likely on the order of 2–4 km in diameter and half a kilometer deep. The blast wave from the impact would radiate outward, carrying enough force to flatten structures and forests for dozens or even hundreds of kilometers in every direction. In the immediate vicinity of ground zero, temperatures would briefly rival those of the Sun as the impact generates a searing fireball. Anything near the impact site – towns, forests, or whatever unfortunate locale – would be vaporized or reduced to charred ruins in an instant. An Apophis impact is estimated to cause “widespread destruction up to several hundred kilometers from its impact site,” according to experts. In practical terms, that means an entire metropolitan region could be obliterated. One study noted that the force of the impact could devastate an area about the size of Central Europe – an almost inconceivable swath of destruction. The shock wave in the air would shatter windows and level buildings at great distances. Simultaneously, intense thermal radiation would ignite fires over a large area, and violent ground shaking (equivalent to a major earthquake) would rip through the Earth’s crust around the impact zone. In this hellish moment, virtually nothing in the immediate impact region would survive. For a comparison, the 1945 atomic bomb blasts were about 15–20 kilotons; an Apophis impact would be on the order of 1,000,000 kilotons. The devastating blast, heat, and seismic shock of such an event defies easy description – it is the kind of catastrophe humanity has never witnessed first-hand, one that thankfully occurs only on geologic timescales.

Earth’s surface is 70% ocean, and statistically an asteroid like Apophis would be more likely to impact at sea than on land. If Apophis plunged into an ocean, it would still release the same monstrous energy – but the effects would play out differently. The impact would instantly vaporize enormous quantities of water, gouging out a transient cavity in the ocean. This would spawn towering tsunami waves in all directions. Near the impact site, the initial tsunami could be on the order of hundreds of meters high– a dome of water blasted upward and then collapsing. This tallest wave would quickly break and send a series of mega-tsunamis racing across the ocean. Even as they spread outward and lose some height, the waves would remain extremely dangerous, potentially still tens of meters high when they reach coastlines. “If the impact occurs in the ocean, it can generate hazardous tsunamis,” notes Gareth Collins, a planetary scientist. These waves could travel thousands of kilometers. Hours after the impact, shorelines on multiple continents could be struck by destructive walls of water. Low-lying coastal regions would be inundated; ports and cities near the sea could be wiped out by the deluge. The devastation would not be confined to one nation – it would be a global tsunami disaster, with heavily populated coasts around the world facing intense flooding. An ocean impact would spare humanity the worst of the dust and soot (since much of the ejecta would be water vapor), but in terms of immediate destruction, worldwide tsunami damage could make Apophis’s impact felt on a nearly global scale. The Indian Ocean tsunami of 2004, for instance, killed over 200,000 people with waves a few tens of meters high; an Apophis-induced tsunami could be far taller and more energetic at the source, exponentially increasing the potential destruction along coastlines. It’s a sobering thought: even without forming a crater on land, an ocean strike by a 370 m asteroid could wreak havoc on civilization.

Beyond the local and regional devastation, an asteroid impact the size of Apophis would have significant global repercussions. The colossal explosion would loft millions of tons of dust, aerosols, and vaporized material high into Earth’s atmosphere. If the impact is on land, pulverized rock and soot from widespread fires would darken the skies; if in the ocean, vaporized seawater and sea-floor debris would likewise inject into the stratosphere. In either case, the planet would likely experience a period of cooler temperatures and diffused sunlight – an “impact winter” scenario. Climate models suggest that the dust and particles from an impact can encircle the globe, blocking a portion of sunlight for months to years. In this hypothetical case, drastic climate changes could follow. Crops might fail in multiple regions as growing seasons shorten. There could be worldwide food shortages and disruptions to ecosystems. While an Apophis-scale impact is not an existential threat to humanity as a whole (our species would likely survive), it could still be the worst disaster in modern history, potentially killing millions directly and causing economic and environmental turmoil for years afterward. For context, the Chicxulub impact that ended the Cretaceous period lofted so much sulfur and dust that it caused a “worldwide blackout” and a decade of winter-like conditions, leading to the mass extinction of dinosaurs. An Apophis impact would be far less severe than Chicxulub’s apocalypse, but it would still mark a turning point in history – a smaller-scale global climate shock followed by likely social upheaval. The sky might glow with strange hazes and brilliant sunsets from high-altitude dust. Acid rain could fall from chemical reactions in the stratosphere. In short, the entire planet would feel the effects of a large asteroid impact, underscoring why Earth’s past collision events (and the potential for future ones) are taken so seriously by scientists.

To truly appreciate the power of a hypothetical Apophis impact, it helps to compare it with historical impacts. On the lower end, we have events like the Tunguska explosion of 1908, when a relatively small asteroid (~50 meters) blew up in the atmosphere over Siberia. Tunguska released an estimated 10–15 megatons of energy, flattening over 2,000 square kilometers of remote forest. No crater was left (since it was an airburst), but the damage on the ground was immense – yet Tunguska’s energy was only perhaps 1% of Apophis’s. On the upper extreme, there’s the Chicxulub impact 66 million years ago, caused by a ~10 km asteroid. Chicxulub released on the order of 10^8 megatons (roughly 100,000,000 megatons) of energy, literally hundreds of millions of times more powerful than a hypothetical Apophis impact. It created a crater 180 km wide and ushered in mass extinction. In comparison, an Apophis strike – around 1,000–2,000 megatons – sits in the middle of the spectrum of impact events. It is far more devastating than any nuclear bomb or recent meteor event, capable of destroying a major region or causing global shockwaves, but it is not cataclysmic enough to wipe out life across the planet. Scientists often mention the Tunguska event as a reminder that even “small” asteroids can do great damage, and the Chicxulub event as proof that larger ones can transform the entire biosphere. Apophis represents a class of impactor that, while not “doomsday” on a planetary scale, could easily cause a disaster beyond anything humanity has ever experienced. It’s the kind of impact that occurs maybe once in 100,000 years, which is why the world’s astronomers diligently search for and track objects of this size. In fact, Apophis’s discovery spurred advances in asteroid tracking and planetary defense planning, ensuring we are better prepared for any future asteroid on a collision course.

Embracing the Wonders and Warnings of the Cosmos

The story of Apophis in 2029 is one of both wonder and caution. On one hand, the close approach will be a spectacular reminder of our cosmic neighborhood in motion – a chance for people everywhere to look up and see a distant world briefly visit our skies. It’s a moment to marvel at the fact that we live on a planet amidst countless other objects, large and small, whirling around the Sun. Apophis is a leftover fragment from the solar system’s formation, and its flyby connects us to deep time and the broader dance of planets and asteroids. On the other hand, Apophis’s flyby is also a celestial wake-up call: a tangible demonstration that Earth has been in the cosmic crosshairs before and will be again. Our planet bears the scars of past impacts – from the gigantic craters of ancient collisions to the more recent Tunguska blast. These events have shaped the course of life’s evolution and remind us that catastrophic impacts, while rare, are real. The 2029 Apophis encounter, thankfully, is a close shave and not a collision, allowing us to safely appreciate the event’s grandeur. In its aftermath, humanity can take inspiration to invest in planetary defense, improved asteroid detection, and perhaps future missions to asteroids (indeed, plans are already in motion to send a probe to Apophis during its visit). Ultimately, the saga of Apophis invites us to feel humility and awe. We are spectators to a dynamic universe where rocks the size of mountains can pass by at blistering speeds, and where the fate of our world has, in epochs past, been altered by celestial impacts. Come 2029, as Apophis streaks across the night, eyes will turn skyward across the globe. For a brief time, our bustling civilization will pause to watch a mountain in the sky and reflect on the thin margin that separates a beautiful cosmic encounter from a civilization-threatening disaster. It is a reminder that Earth, our home, travels through a cosmic shooting gallery – but also that with knowledge and preparation, we can keep watch, appreciate the beauty of these visitors, and ensure that events like Apophis remain incredible spectacles rather than tragedies.

Here's the link to our video on What Would Happen if Apophis 2029 Struck Earth: