But as the Chelyabinsk asteroid demonstrated on Feb. 15, objects far smaller can inflict damage. At about 55 feet across, and with a mass estimated at 10,000 tons, the asteroid exploded high over the Ural mountains. The shock waves damaged an estimated 4,300 buildings and injured nearly 1,500 people.
With tens of millions of objects this size orbiting the sun, the recurrence rate for collisions with a Chelyabinsk-like object averages once every 100 years, according to Paul Chodas, with NASA's Near-Earth Objects Program Office at the Jet Propulsion Laboratory in Pasadena, Calif.
Of particular interest to NEOSSat's astronomers are two groups of asteroids, known as Atens and Atiras. Members of both groups started out as asteroids in the main asteroid belt, between Mars and Jupiter. But gravitational interactions or collisions slowed these asteroids down to begin their spiral in toward the sun.
The Atiras have orbits that fall entirely inside Earth's orbit. The Atens' orbits occasionally cross that of Earth. The region of space NEOSSat aims to explore lies between 45 and 55 degrees away from the sun, well inside Earth’s orbit, Dr. Hildebrand notes.
The time available for observing this region from Earth's surface lasts no more than about 30 minutes at a time, often less, Hildebrand says. The regions of interest are so close to the sun that observing time is limited by twilight and dawn.