What Happens If an Asteroid Hits Earth?

The thought of an asteroid hitting Earth sounds like the plot of a disaster movie, but in 2026 it is a question that scientists study with calm precision rather than panic. Space rocks of every size cross our planet’s path constantly, and what actually happens when one arrives depends almost entirely on a single number: its diameter. The vast majority burn up harmlessly as shooting stars, a handful explode in the upper atmosphere, and only the rarest giants ever reach the ground with civilization-altering force.

This guide walks through exactly what an asteroid impact would do at each size, the most famous impacts in history, how often they occur, and how agencies like NASA and ESA now detect and even deflect dangerous objects. The tone here is deliberately factual and reassuring, because the science genuinely supports optimism.

What happens if an asteroid hits Earth?

When an asteroid hits Earth, its kinetic energy — a function of mass and velocity squared — is converted almost instantly into heat, light, and a pressure wave. Objects typically arrive at 11 to 72 kilometres per second, so even a modest rock carries the energy of many nuclear weapons. The outcome ranges from a fleeting fireball to global catastrophe, scaling sharply with diameter.

Smaller bodies never survive the journey. Earth’s atmosphere is a remarkably effective shield, decelerating and vaporising most incoming rock before it reaches the surface. The trouble only begins when an object is large enough to punch through that protection.

The three outcomes of an impact

• Burn-up: Pebbles to boulders (under a few metres) disintegrate as meteors. Dozens strike the atmosphere daily.
• Airburst: Tens of metres across, the object explodes in mid-air, releasing a shockwave but leaving little or no crater.
• Ground impact: Hundreds of metres and larger reach the surface, excavating craters and, at the extreme, triggering global effects.

How do impact effects change with asteroid size?

Asteroid impact effects scale dramatically with diameter because energy grows with the cube of size. Doubling an asteroid’s width multiplies its mass — and roughly its destructive energy — by about eight. That is why a 20-metre rock and a 140-metre one belong to entirely different threat categories, even though both sound small against the scale of a planet.

The table below summarises the well-studied relationship between size and consequence. These figures come from impact modelling and the historical record, and they are the foundation of how planetary defence experts prioritise threats.

The pattern is clear and oddly comforting: the truly dangerous objects are also the rarest, and the common objects are mostly harmless. The danger zone we watch most closely sits in the 140-metre-and-up range, where impacts are infrequent but consequential.

What were the most famous asteroid impacts in history?

History gives us three benchmark events that anchor the entire conversation about an asteroid hitting Earth. Each represents a different size class, and together they show how the science moves from local nuisance to planetary catastrophe.

Chelyabinsk (2013): the modern wake-up call

On 15 February 2013, a roughly 20-metre asteroid entered the atmosphere over Chelyabinsk, Russia, and exploded about 30 kilometres up. The airburst released energy equivalent to roughly 400–500 kilotons of TNT. No one was killed, but the shockwave blew out windows across the city, injuring around 1,500 people, mostly from flying glass. Crucially, the object arrived from the direction of the Sun and was never detected in advance — a gap that surveys are still working to close.

Tunguska (1908): the largest in recorded history

The Tunguska event flattened an estimated 2,000 square kilometres of Siberian forest — about 80 million trees — when an object perhaps 50 to 60 metres across detonated in the air. No crater was ever found, confirming it was an airburst. Had it struck over a major city, casualties would have been enormous. It remains the clearest illustration of why even a “small” near-Earth object deserves attention.

Chicxulub (66 million years ago): the dinosaur killer

The Chicxulub impactor, around 10 kilometres wide, struck what is now the Yucatán Peninsula in Mexico. It carved a crater more than 180 kilometres across and ejected enough debris to darken the skies worldwide, triggering an “impact winter” that ended the age of the dinosaurs. This is the event people picture when they imagine the worst — and it is also the kind of impact we can now be confident is not lurking undetected, because objects that large are easy to find and we have catalogued essentially all of them.

To understand where these intruders come from, it helps to know our cosmic neighbourhood. Our explainer on the structure of the solar system shows how the main asteroid belt between Mars and Jupiter feeds the population of rocks that occasionally wander inward.

How likely is an asteroid hitting Earth?

A civilization-threatening asteroid hitting Earth is extremely unlikely in any human lifetime, and — this is the key point — no known asteroid poses a significant impact threat for at least the next 100 years. That statement comes directly from NASA’s impact-monitoring systems, which continuously track every catalogued near-Earth object decades into the future.

Probability scales inversely with size. Small, harmless meteors arrive constantly; a Chelyabinsk-class airburst happens somewhere on the planet every few decades; a Tunguska-class event every few centuries; and a true global catastrophe only on timescales of hundreds of thousands to millions of years. Statistically, you are far more likely to be affected by ordinary natural hazards than by a space rock.

What about Apophis in 2029?

The asteroid 99942 Apophis, about 340 metres across, will make a famously close pass on 13 April 2029, sweeping within roughly 32,000 kilometres of the surface — closer than some geostationary satellites. It will be visible to the naked eye from parts of Europe, Africa, and Asia. To be absolutely clear: Apophis will miss Earth. Radar observations in 2021 ruled out any impact risk for at least a century. Far from a threat, it is a once-in-a-lifetime scientific and observing opportunity, which is why 2029 has been designated a year of international asteroid awareness.

How do we detect near-Earth objects?

We detect near-Earth objects using a global network of survey telescopes that scan the night sky for moving points of light, then refine each object’s orbit over time. When a new object is found, astronomers calculate its trajectory and project it forward; NASA’s automated Sentry system at the Center for Near-Earth Object Studies (CNEOS) flags any with even a remote chance of impact.

Surveys such as Pan-STARRS and the Catalina Sky Survey discover thousands of new objects each year. The headline achievement: more than 95% of the largest, most dangerous asteroids — those over one kilometre — have already been found and confirmed to be safe. The remaining effort focuses on the smaller but still hazardous 140-metre class, a gap that future space-based infrared telescopes are designed to fill.

Where the catalogue still has blind spots

• Sun-direction objects: Asteroids approaching from the daytime sky are hard to see, as Chelyabinsk demonstrated.
• Small dark rocks: Objects tens of metres across reflect little light and can stay hidden until close.
• Solution in progress: Infrared space telescopes positioned to look back toward the Sun will dramatically improve early warning.

Asteroids are only one class of wanderer. For how icy visitors differ from rocky ones, see our companion piece on comets and their orbits, which behave quite differently as they near the Sun.

What is planetary defence and does it work?

Planetary defence is the coordinated international effort to detect, track, and — if necessary — deflect an asteroid on a collision course, and in 2026 we know it works because we have tested it. The strategy rests on a simple principle: with enough warning, a tiny nudge years before a predicted impact is enough to make an asteroid miss Earth entirely.

NASA’s DART mission: proof it works

On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) deliberately crashed a spacecraft into Dimorphos, a 160-metre moonlet orbiting the larger asteroid Didymos. The goal was to measure whether a kinetic impact could change an asteroid’s orbit. The result exceeded expectations: Dimorphos’s orbital period was shortened by about 33 minutes — far more than the 73-second minimum NASA had set as success. The plume of ejected debris added extra push, proving the kinetic-impactor technique is not only viable but efficient. It was humanity’s first demonstration that we can actively alter an asteroid’s path.

ESA’s Hera mission: the follow-up survey

The European Space Agency’s Hera mission, launched in October 2024, is en route to the Didymos system to study the aftermath of the DART collision up close. By precisely measuring Dimorphos’s new orbit, the crater, and the asteroid’s mass and composition, Hera will turn DART’s one-off experiment into a repeatable, well-understood deflection technique. Together, DART and Hera form the first complete planetary-defence test campaign.

Other deflection concepts

• Kinetic impactor: Ram the asteroid with a spacecraft — proven by DART.
• Gravity tractor: Park a spacecraft nearby and let its gravity slowly tug the asteroid off course.
• Nuclear standoff: A last-resort option for very large objects or short warning times, detonating a device nearby to vaporise surface material and create thrust.

A first-hand note on how amateurs help

I’m Hamza Touhami, and I’ve been doing astrophotography since 2008. People are often surprised to learn that amateur observers genuinely contribute to near-Earth object science. When professional surveys discover a new asteroid, its orbit is initially uncertain — and that is where the amateur community steps in, supplying follow-up astrometry that pins the orbit down before the object fades from view. From my own remote rig, tracking a fast-moving target and timing its position is demanding but deeply rewarding work.

One of the most valuable amateur activities is occultation timing: recording the precise moment an asteroid passes in front of a background star. Combining timings from observers spread across a region lets astronomers reconstruct an asteroid’s exact size and shape — data that even large telescopes struggle to capture. It is a real example of how careful backyard work feeds directly into planetary defence, and it is part of why I keep pointing my equipment at the sky.

What should you actually do about asteroid risk?

For an individual, the rational response to asteroid risk is essentially nothing — beyond enjoying the science. The probability of being harmed by an impact in your lifetime is vanishingly small, the largest threats are already catalogued and cleared, and for the first time in history we possess a tested method to deflect a dangerous object. This is one global hazard where the trend lines are firmly positive.

If you want to engage productively, channel curiosity instead of fear. Follow CNEOS impact-monitoring updates, learn the night sky, or even join an occultation-timing campaign. Understanding our neighbours — from the major planets to the smaller bodies — turns a vague dread into informed appreciation.

Key takeaways

• Most asteroids burn up; only objects over ~140 metres are seriously hazardous.
• No known asteroid threatens Earth for at least the next 100 years.
• Apophis will pass close on 13 April 2029 but will not hit Earth.
• DART proved in 2022 that we can deflect an asteroid; Hera is studying the result.
• Amateur astronomers help by tracking and timing near-Earth objects.

To keep exploring the rocky frontier of our system, browse our growing guides on the asteroid belt and near-Earth objects and on the Moon’s own cratered history, which records billions of years of impacts that Earth’s weather has long since erased.

For authoritative, continually updated information, see NASA’s Planetary Defense Coordination Office, the ESA Planetary Defence programme, and the Britannica entry on Apophis.

Frequently asked questions

Could an asteroid destroy Earth?

No asteroid in the solar system is large enough to literally destroy the planet. Even the 10-kilometre Chicxulub impactor that ended the dinosaurs left Earth intact, though it caused a mass extinction. Such giant impacts occur only once every 100 million years or more, and no object of that size is on a collision course.

Will an asteroid hit Earth in 2029?

No. The well-known asteroid Apophis will pass extremely close to Earth on 13 April 2029 — within about 32,000 kilometres — but radar measurements have ruled out any impact for at least a century. The 2029 flyby is a safe, spectacular observing opportunity, not a threat.

What is the biggest threat from a small asteroid?

The main danger from a small asteroid is an airburst, like the 2013 Chelyabinsk event over Russia. A 20-metre rock exploding in the atmosphere can shatter windows and injure people across a city with its shockwave, even without forming a crater. Larger objects in the 60-metre Tunguska class can flatten forests over thousands of square kilometres.

Can we stop an asteroid from hitting Earth?

Yes, with enough warning. NASA’s DART mission proved in 2022 that crashing a spacecraft into an asteroid can change its orbit — it shifted the moonlet Dimorphos by about 33 minutes. Other methods, like a gravity tractor, could nudge an asteroid years in advance so it safely misses Earth.

How does NASA find dangerous asteroids?

NASA and partner surveys scan the sky nightly for moving objects, then calculate their orbits decades into the future. The automated Sentry system at CNEOS flags any object with even a tiny impact chance. Over 95% of the largest, most dangerous near-Earth asteroids have already been discovered and confirmed safe.