Astronomers estimate it would take at least five years to deflect an asteroid on a collision course with Earth. More cautious experts suggest a full decade. But are our current technologies up to the task?
A few weeks ago, NASA's Jet Propulsion Laboratory Center for Near-Earth Object Studies (CNEOS) conducted a biennial planetary defense exercise simulating an asteroid impact. Teams collaborated to respond to an evolving threat scenario.
This year's fictional asteroid, "2021 PDC," was discovered on April 19, 2021, at 57 million km from Earth. Its closest approach was projected for October 20, 2021—just six months later. The outcome: widespread destruction across central Europe.
Though simulated, the exercise delivered a stark reality check: no current technology could stop such an asteroid in that timeframe. This raises a critical question: how much advance warning do we truly need?
"Five years is the absolute minimum," states Paul Chodas, a key leader in the simulation and manager at NASA's CNEOS. He's among the optimists; MIT astronomer Richard Binzel advocates for at least 10 years. "Time is the most valuable resource when facing a real asteroid threat," Binzel told Business Insider.
In the simulation, participants learned the asteroid's size just a week before "impact." A 35-meter rock might airburst in the atmosphere, but a 500-meter behemoth could obliterate a city.
Thus, rapid detection is paramount, allowing time to assess size, speed, and trajectory for tailored defenses.
Prioritizing robust sky surveillance is essential to buy that time. Progress is underway, but gaps remain. In 2005, U.S. Congress tasked NASA with cataloging 90% of near-Earth objects (NEOs) larger than 140 meters. As of two years ago, NASA had identified about 40% of the estimated 25,000 such objects.
Three primary deflection strategies exist: 1) Detonate an explosive nearby to fragment the asteroid; 2) Use lasers to vaporize surface material and alter its path; 3) Ram it with a spacecraft for kinetic impact.
NASA and ESA are testing the third via the DART (Double Asteroid Redirection Test) mission, targeting Dimorphos, moonlet of asteroid Didymos. A spacecraft will intentionally collide with Dimorphos in 2022. ESA's follow-up Hera mission will evaluate results years later.
Yet, any of these methods requires years to develop and deploy. "From concept to launch and rendezvous takes multiple years—even then, trajectory changes unfold over one to two orbits," Chodas explains.
Proactive monitoring remains our best defense. NASA's NEO Surveyor mission, featuring an infrared telescope for detecting dark asteroids, is slated for launch in 2026. Soon, the Vera C. Rubin Observatory will accelerate discoveries of thousands more NEOs.
