An asteroid is a rocky object that orbits the Sun. Most asteroids are found in the main asteroid belt located between Mars and Jupiter, though some have orbits that bring them closer to Earth. These celestial bodies vary significantly in size and shape, ranging from small pebbles to objects hundreds of miles in diameter. The Moon, Earth’s only natural satellite, orbits our planet at an average distance of about 384,399 kilometers (238,854 miles). It plays a role in stabilizing Earth’s axial tilt, which contributes to our planet’s stable climate. The Moon’s surface is heavily cratered, providing a record of past impacts from asteroids and comets.
Immediate Lunar Impact
If an asteroid were to strike the Moon, the immediate physical consequences on the lunar surface would be dramatic. A new impact crater would form at the collision site, its size depending on the asteroid’s mass, velocity, and the geology of the Moon’s surface; for impacts in the inner solar system, a very rough rule of thumb suggests that craters can be approximately 10 to 20 times larger in diameter than the impacting object. The immense energy released during the impact would also generate moonquakes, seismic waves rippling across the lunar surface. A massive plume of dust, rock, and debris, known as ejecta, would be launched from the impact site into space. Extreme temperatures would vaporize some lunar material and asteroid fragments, creating a bright flash observed during impact events.
Short-Term Global Effects
The impact would be observable from Earth as a bright flash of light, caused by a small fraction of the impactor’s kinetic energy converting into visible light. Following the flash, a temporary ejecta cloud might also be visible. There is a possibility of lunar ejecta, such as dust and small rocks, entering Earth’s atmosphere, which could result in temporary meteor showers or an increase in micrometeoroid flux; however, larger pieces of lunar material are unlikely to reach Earth directly unless the impact was exceptionally large and specifically directed. For any realistically plausible asteroid impact, the Moon’s orbit around Earth would remain largely unaffected, as its immense mass means that even a significant asteroid collision would have very little effect on its motion. Similarly, the Moon’s gravitational pull on Earth’s ocean tides would not change significantly, as tidal forces depend on the Moon’s overall mass and distance, which would remain constant.
Lasting Changes to the Moon
The most evident lasting change on the Moon would be the formation of a permanent new crater. This crater would become a prominent feature on the lunar landscape. For example, the failed Russian Luna 25 mission in 2023 created a new crater approximately 10 meters in diameter, which was observed by NASA’s Lunar Reconnaissance Orbiter. The exposed fresh rock and dust from the impact site could alter the Moon’s surface reflectance, known as albedo, creating a brighter or darker patch around the new crater. The widespread distribution of ejecta from the impact would also contribute to lunar surface resurfacing, altering the existing layer of regolith, the Moon’s powdery surface material. Such an asteroid impact would present unprecedented opportunities for lunar science and observation. Scientists could study the fresh crater and its ejecta to gain insights into the Moon’s subsurface composition and the mechanics of impact events. Observing such an event would also refine our understanding of the current impact rate in the Earth-Moon system, which is important for future lunar missions.