Giant Comets Periodically Smash Earth, Scientists Say

Giant comets that originate in the planetary fringes of the solar system pose a greater threat of colliding with Earth than do asteroids, which originate closer to the sun, a new review paper argues. No centaur poses a known immediate threat to Earth, but the discovery of this massive population has led a group of astronomers to re-assess the threat of these seemingly distant bodies to this planet. Estimates currently suggest that one of these giant comets crosses Earth's orbit on average only o