Most asteroids do not threaten Earth. Planetary defense focuses on discovering the small fraction whose orbits merit closer observation and developing response options before an emergency occurs.
Early detection is the most important advantage.
Finding near-Earth objects
Survey telescopes repeatedly photograph the sky and identify points of light that move against background stars. Follow-up observations allow astronomers to refine an object’s orbit and estimate where it will travel.
An initial risk calculation can change as new measurements arrive. A newly discovered asteroid appearing on a risk list does not mean a collision is expected; additional data often rule it out.
Size, speed, composition and impact location would determine the possible consequences.
DART tested one deflection method
NASA’s DART spacecraft deliberately struck Dimorphos, the small moon of asteroid Didymos, in September 2022. Neither object threatened Earth.
The impact shortened Dimorphos’s orbit around Didymos by more than 30 minutes. It also changed the moonlet’s shape. This demonstrated that a kinetic impactor can alter an asteroid’s motion.
DART did not blow up the asteroid. The goal was to produce a small, measurable orbital change.
Warning time changes the options
A slight deflection performed years in advance may be enough for an asteroid to miss Earth. With less warning, the same method may not provide sufficient change.
A real response would depend on:
- The reliability of the predicted orbit
- Available warning time
- Size and internal structure
- Rotation and composition
- Launch capability
- International coordination
Other proposed methods include using a spacecraft’s gravity to slowly alter an orbit. More extreme options involve additional technical, political and legal complications.
Preparedness without alarm
Planetary defense requires telescopes, accurate public communication and missions that test technologies before they are needed.
DART proved one technique, not a universal solution. Its main lesson is that asteroid hazards can sometimes be reduced when objects are discovered early and studied carefully.
Sources
- NASA DART mission: https://science.nasa.gov/planetary-defense-dart/
- NASA study of Dimorphos after impact: https://www.nasa.gov/missions/dart/nasa-study-asteroids-orbit-shape-changed-after-dart-impact/
- NASA Planetary Defense Strategy: https://www.nasa.gov/wp-content/uploads/2023/05/nasa-planetary-defense-strategy-final-508.pdf