💥 Hitting the moon to deflect the entire binary system

Intentionally hitting an asteroid's moon allows for a lasting change in the primary asteroid's orbit around the Sun. This is one of the results from the experiment conducted by NASA's DART mission.

The probe's impact not only succeeded in altering the orbit of a small asteroidal moon; it also slightly deflected the trajectory of the entire binary system in space. An observation that is encouraging for our future ability to protect Earth from potentially hazardous celestial objects.


In 2022, the DART probe intentionally collided with the asteroid Dimorphos, which orbits a larger companion named Didymos. This maneuver aimed to verify if a kinetic impact could deflect such a body, and the results exceeded all expectations. Dimorphos's orbit around Didymos was shortened by more than thirty minutes.

An in-depth analysis shows the impact generated a debris cloud, called ejecta, which amplified the initial thrust. Called the momentum amplification factor, this phenomenon nearly doubled the effect on Dimorphos. As a consequence of this additional impulse, the entire asteroid duo saw its path around the Sun slightly altered, with a minimal but detectable speed change over long periods.

To measure these minute alterations, amateur astronomers worldwide mobilized between 2022 and 2025. They observed stellar occultations, moments when the asteroid passes in front of a star, allowing for precise calculation of the new trajectories. Their contribution proved crucial in confirming that DART indeed affected the movement of the binary system within the Solar System.


This same data also allowed for estimating the density of both bodies. Didymos is revealed to be denser, at about 162 pounds per cubic foot (2600 kilograms per cubic meter), while Dimorphos, at only about 96 lbs/ft³ (1540 kg/m³), more closely resembles a loosely aggregated pile of rubble. This difference supports the hypothesis that Dimorphos was born from material ejected from Didymos.

These results reinforce the idea that missions of this type could one day protect Earth from a collision. For its part, NASA plans to launch the NEO Surveyor telescope after 2027 to detect a greater number of asteroids near us, thus combining surveillance and action for a more comprehensive planetary defense.

Kinetic Impactor Technology

The principle of kinetic impactors, like the DART probe, relies on using the force of a collision to alter an asteroid's trajectory. This approach is based on a simple physical foundation: by striking the object at very high speed, momentum is transferred to it, which can bend its path. It proves particularly suitable for intermediate-sized bodies, for which a nuclear explosion would present too many risks or be ineffective.

Its main strength lies in its technical simplicity. A probe can be launched several years in advance, precisely targeting the asteroid for a perfectly controlled impact. Future missions could even combine several impactors or rely on observation satellites to adjust the trajectory in real time, thereby increasing the chances of success.

Nevertheless, its effectiveness remains dependent on parameters such as the asteroid's composition. A dense, solid object does not react the same way as a loose debris pile, like Dimorphos. Numerical simulations allow for anticipating these distinct behaviors, but real-world tests remain essential to refine the models.

Concretely, this technology fits into a broader planetary defense strategy. It could be used in conjunction with other methods, such as gravitational tractors, to offer an adaptable response to the diversity of threats from space.