Planetary securityCelestial hazards: Twenty years of planetary defense
NASA’s Center for Near-Earth Object Studies was established in 1998 to fulfill a 1998 Congressional request to detect and catalogue at least 90 percent of all NEOs larger than one kilometer in size (roughly two-thirds of a mile) within 10 years. In 2005, Congress established a new, much more ambitious goal for the NEO Observations Program — to discover 90 percent of the NEOs down to the much smaller size of 450 feet (140 meters), and to do so by the year 2020. There are now over 18,000 known NEOs and the discovery rate averages about 40 per week.
NASA’s Center for Near-Earth Object Studies enters its third decade.
On 11 March 1998, asteroid astronomers around the world received an ominous message: new observational data on the recently discovered asteroid 1997 XF11 suggested there was a chance that the half-mile-wide (nearly one kilometer) object could hit Earth in 2028.
The message came from the Minor Planet Center, in Cambridge, Massachusetts, the worldwide repository for such observations and initial determination of asteroid orbits. And although it was intended to alert only the very small astronomical community that hunts and tracks asteroids to call for more observations, the news spread quickly.
Most media outlets did not know what to make of the announcement, and mistakenly highlighted the prospect that Earth was doomed.
Fortunately, it turned out that Earth was never in danger from 1997 XF11. After performing a more thorough orbit analysis with the available asteroid observations, Don Yeomans, then the leader of the Solar System Dynamics group at NASA’s Jet Propulsion Laboratory in Pasadena, California, along with his colleague Paul Chodas, concluded otherwise. “The 2028 impact was essentially impossible,” said Chodas, who is now director of NASA’s Center for Near-Earth Object Studies (CNEOS), located at JPL.
“To this day we still get queries on the chances of XF11 impacting in 2028,” Chodas said. “There is simply no chance of XF11 impacting our planet that year, or for the next 200 years.”
Chodas knows this thanks to CNEOS’ precise orbit calculations using observation data submitted to the Minor Planet Center by observatories all over the world that detect and track the motion of asteroids and comets. For the past two decades, CNEOS calculations have enabled NASA to become the world leader in these efforts, keeping close watch on all nearby asteroids and comets — especially those that can cross Earth’s orbit.
“We compute high-precision orbits for all asteroids and comets and map their positions in the Solar System, both forward in time to detect potential impacts, and backward to see where they’ve been in the sky,” Chodas said. “We provide the best map of orbits for all known small bodies in the Solar System.”
Mapping the celestial hazard
Near-Earth Objects (NEOs) are asteroids and comets in orbits that bring them into the inner solar system, within 121 million miles (195 million
