© NASA/Goddard/University of Arizona/Lockheed MartinBennu ejecting particles from its surface on Jan. 19, 2019.
Every day, thousands of small rocks — dust grain- to pebble-sized — cross paths with Earth's atmosphere and burn up. More organized collisions, known as meteor showers, are visible to us when the planet passes through whole clouds of rocky debris.
These fragments were long thought to come strictly from comets whose crusts had been heated by the Sun and cracked open. But early in 2019, NASA's
OSIRIS-Rex spacecraft (short for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) captured
images from the near-Earth asteroid Bennu that flipped that line of thinking on its head.
The images showed small bits of rock launching off the asteroid's surface. Some of the rock fell back to the surface and some went into orbit around Bennu for several days, but
about 30 percent was ejected with enough speed that its pieces escaped the asteroid's gravity and began to orbit around the Sun."This was surprising," says Robert Melikyan, a graduate student at the University of Arizona's Lunar and Planetary Laboratory. "Bennu doesn't have a lot of volatile material that can heat up and break up the way comets do."
Melikyan and a team of researchers modeled the evolution of the asteroid's dust cloud in a study
published in the Journal of Geophysical Research: Planets earlier this year and
found that the particles both spread out around Bennu's orbit and follow a similar elliptical path around the Sun.
