The solar system is littered with natural debris—asteroids, comets and pieces of the same that occasionally wind up in the steamrolling path of one of the planets. When a piece of debris encounters the friction of Earth's atmosphere, it flares up as a meteor, or shooting star, and pieces of the object may survive the heat of reentry to reach the surface as meteorites.
Many more objects whiz past Earth without striking the atmosphere, perhaps returning for another pass some years later. Many of those go undetected, especially the small asteroids that are harder to spot with the relatively modest telescopes that keep watch for near-Earth objects.
But sky monitors did spot one small asteroid, called 2011 CQ1, less than a day before it buzzed Earth at the smallest distance ever recorded. On February 4, the meter-size rock flew over the Pacific at an altitude of about 5,500 kilometers—about one-seventieth the distance between Earth and the moon and well below the orbit of some high-flying satellites.
But even though 2011 CQ1 skirted immolation in Earth's atmosphere, it did not escape from the encounter unmolested. Earth's gravity gave the asteroid a good tweak, redirecting its trajectory by about 60 degrees in much the same way that interplanetary spacecraft use the gravity of the planets for course corrections or speed adjustments. "Prior to the Earth close approach, this object was in a so-called Apollo-class orbit that was mostly outside the Earth's orbit," asteroid trackers Don Yeomans and Paul Chodas wrote on the NASA Near-Earth Object Program Web site. "Following the close approach, the Earth's gravitational attraction modified the object's orbit to an Aten-class orbit where the asteroid spends almost all of its time inside the Earth's orbit."
Just what is in store for the tiny asteroid is unclear—faint as 2011 CQ1 is, it was visible only briefly, when it was very close to Earth, and its newly adjusted orbit is not well understood.
Orbital diagram of 2011 CQ1's encounter with Earth: NASA