Before we get too enthusiastic about NASA’s asteroid deflection test, it’s important to remember that we’re terrible at forecasting impacts.
Since 1988, more than 1,200 NASA’s asteroids larger than a meter have collided with our planet. These weren’t large enough to fully destroy the earth or create an extinction event (experts are confident that nothing like that will occur in the next 100 years), but they were large enough to wreak significant harm.
However, humanity only predicted five of those hits in advance – possibly six if we add the object known as A106fg, which may have merely been a near approach – accounting for fewer than 0.42 percent of all strikes on the globe. We won’t be able to deflect asteroids that we aren’t aware of.
Even the five asteroids that were identified just hours before they collided with Earth were discovered with only a few hours to spare. Our existing detection methods have never given us more than a day’s notice, however, experts hope and expect this to change in the future.
The time between discovery and impact is much shorter than the five years between NASA’s approval of the DART mission and its planned rendezvous with Dimorphos next year.
We wouldn’t be able to deflect an asteroid off course with so short notice, and we wouldn’t be able to evacuate individuals who would be affected by the collision.
Because of the limitations imposed by physical constraints, our capacity to detect asteroids before they collide with the earth is still in its infancy.
In order to survey asteroids in the dark of space in our solar system, they must reflect light towards us, which is determined by their closeness to the sun and the phase of the moon.
If they approach us from an angle where we can’t see them coming, they will strike without notice, perhaps causing massive damage.
Asteroid impacts are so powerful that they are generally detected by technology meant to check for secret nuclear tests when they occur over the ocean or in distant sections of the world.
However, when they occur in populated places, they are sometimes observed by those who are directly touched by the impact.
A meteor burst in the atmosphere in Chelyabinsk, Russia, in 2013, causing a massive fireball, shattering windows, and potentially causing over a thousand people to seek medical care for their indirect injuries.
That asteroid was estimated to be over 20 meters in diameter and went completely unnoticed before entering the atmosphere.
It erupted with 30 times the energy of the Hiroshima nuclear weapon at an altitude of 30 kilometers, briefly outshining the sun in the skies over the Ural region.
The Chelyabinsk meteor caused “an airburst and shockwave that rocked six cities across the country – and [sent] a strong reminder that deadly objects can enter Earth’s atmosphere at any time,” according to the Johns Hopkins Applied Physics Laboratory.
“Astronomers believe there are tens of thousands of near-Earth asteroids that are 500 feet (150 meters) diameter or more, large enough to cause regional havoc if they impact Earth.”
“The Chelyabinsk object was only around 60 feet (18 meters) broad, illustrating that even small asteroids may be dangerous – and emphasizing the importance of real-world testing of space-based planetary defense systems,” the institution noted.
While the incident revealed that tiny asteroids can be dangerous, missions like DART show that our planetary defenses are not yet capable of protecting them.
Thousands of people might be killed in a similar explosion in a city like New York or London, especially if the structural integrity of a huge structure is compromised. We simply wouldn’t see it coming at the moment.