When an asteroid could hit earth?
Smaller asteroids hit Earth on a regular basis. Scientists say an asteroid larger than three meters hits Earth about once a year. Strikes from larger asteroids are much rarer; an asteroid larger than 30 meters only strikes Earth about once a century.

Truly disastrous asteroid strikes are very rare, and space agencies like NASA are have found many of the larger asteroids in the solar system. For now, none of those bodies are on course to hit Earth. Nonetheless, the chance is not zero, and some efforts have been made to investigate technology that could deflect an asteroid on a collision course with our planet.