Impact Risk
Will an asteroid
hit Earth?
The short answer: no known asteroid is on a collision course with Earth. Here is the full picture - what the science says, what history shows, and how NASA would respond if the situation changed.
How NASA tracks dangerous asteroids →The current situation
NASA's Center for Near Earth Object Studies (CNEOS) tracks more than 38,000 near-Earth objects. None carry a meaningful probability of impact in the next 100 years. The Torino Scale - the standard measure of asteroid threat level - sits at 0 for every currently known object.
How impact risk is calculated
When a new near-Earth object (NEO) is discovered, astronomers measure its position across multiple nights. Those positions feed into orbital mechanics software at NASA's Jet Propulsion Laboratory, which fits a trajectory to the data and projects it forward in time.
Early observations carry uncertainty - the orbit is not yet well-pinned. That uncertainty translates into a range of possible future positions. If Earth falls within that range on some future date, the object gets an initial non-zero impact probability and appears on CNEOS's risk table.
Follow-up observations over the next days, weeks, or years narrow the orbit. For the overwhelming majority of objects, the refined orbit shows Earth is not in the path. The impact probability drops to zero and the object is removed from the risk table. This is the normal sequence of events - not a cover-up, but the expected result of better data.
How often do impacts happen?
Impacts occur on a spectrum. Small objects arrive constantly; large ones are rare.
| Object size | Approximate frequency |
|---|---|
| < 25 m | Every few years |
| 25–140 m | Every few hundred years |
| 140 m – 1 km | Every few thousand years |
| 1–5 km | Every few hundred thousand years |
| > 5 km | Every tens of millions of years |
What history tells us
Asteroid impacts are not hypothetical. Earth has been struck many times throughout its history. The difference today is that we can see them coming.
The most recent widely felt event was Chelyabinsk in February 2013. An object roughly 20 metres across entered the atmosphere over Russia, releasing energy equivalent to about 500 kilotons of TNT. Its shockwave broke windows across the region and sent around 1,500 people to hospital with cuts from flying glass. The object never reached the ground intact.
In 1908, a larger object - estimated at 50-80 metres - exploded above the Podkamennaya Tunguska River in Siberia. The airburst flattened an estimated 2,000 km² of forest. Had it arrived a few hours later, it would have detonated over a major European city. No one was killed directly, because the region was almost completely uninhabited.
Both of those objects were below the 140-metre threshold NASA uses to define a potentially hazardous asteroid (PHA). Objects of that size and larger - the ones that could cause widespread regional or global damage - are the focus of planetary defence efforts.
What would happen if a threat were confirmed
The most important factor is lead time. With decades of warning, the most practical response is a kinetic impactor - a spacecraft rammed into the asteroid to change its speed by a fraction of a millimetre per second. Small changes in speed, applied early enough, translate into large changes in position by the time the asteroid reaches Earth.
NASA demonstrated this in September 2022 with the DART mission: a spacecraft deliberately crashed into Dimorphos, a 160-metre moonlet of asteroid Didymos, shortening its orbital period by 33 minutes - significantly more than the minimum target. Planetary deflection is not theoretical. It has been tested.
With shorter warning times, options are fewer. A nuclear standoff detonation could disrupt or nudge a smaller object. With little lead time, civil defence (evacuation) becomes the primary tool. This is why finding objects early matters so much - decades of lead time turn an extinction-level threat into an engineering problem.
