NASA reveals chances of an asteroid hitting Earth in next 100 years

Six NASA experts have taken to Reddit for an Ask-Me-Anything (AMA) regarding asteroids, Earth, and the agency's upcoming Double Asteroid Redirection Test (DART) mission.

NASA's upcoming DART mission is the first planetary defense mission from the agency and will involve colliding a small spacecraft around the size of a vending machine into a small asteroid around the size of the Great Pyramid of Giza. The asteroid that is the target is orbiting a larger asteroid, and NASA's goal of the mission is to see if it's possible to alter the orbit of the smaller asteroid. The results from this mission will pave the way forward for planetary defense strategies.

One of the questions that were posed to the six participants was, "What is the probability (mathematical) of a moderate size asteroid impact in the next 100 years?". NASA's Marina Brozovic, an asteroid scientist at JPL, answered and said that the agency doesn't know of any objects that are several hundred meters (200 meters is 656 feet) in size that has a chance of impacting Earth. Additionally, Brozovic reminds everyone that any object smaller than about 100 feet in size is unlikely to reach the ground due to our atmosphere.

Here is Marina Brozovic's answer in full.

Our current knowledge of the impact statistics is the following:

Tunguska-type of event, an asteroid a few tens of meters in size, hundreds of years;

An asteroid several hundred meters in size -- hundreds of thousands to millions of years,

1 km asteroid - several million to tens of millions of years.

We do not currently know of any object of "moderate" size which has a chance of impact in the next 100 years. By moderate, I will assume you mean several hundred meters.

Please keep in mind that anything smaller than about 30 meters in size will have an airburst and is unlikely to reach ground (excluding metallic NEAs). Our atmosphere is very efficient at protecting us from small impacts. -MB