It is highly unlikely that a large asteroid will hit Earth in the foreseeable future. But because the damage from such an event could be great, NASA leads hypothetical asteroid impact roundtable exercises every two years with experts and decision makers from federal and international organizations to address the many uncertainties of an impact scenario. The last exercise took place last April, and a preliminary report was published on June 20.
It is not easy to create such a scenario that will be realistic and useful for all involved. Scientists from NASA's Center for Near-Earth Objects (CNEOS), which specializes in tracking and determining the trajectory of asteroids and comets and testing whether they endanger the Earth, played a central role in planning these exercises from their inception 11 years ago.
"These hypothetical scenarios are complex and involve a lot of work, so our goal is for them to be useful and challenging so that exercise participants and decision makers refine their processes and procedures to quickly arrive at an action plan while addressing gaps in the knowledge of the planetary defense community," said Paul Chodas, director of CNEOS .
This year's scenario: A hypothetical asteroid, perhaps a few hundred meters long, has been discovered and has an estimated 72% chance of hitting Earth within 14 years. Potential impact sites include densely populated areas in North America, southern Europe and northern Africa, but there is still a 28% chance that the asteroid will not hit the country. After a few months of tracking, the asteroid moves too close to the sun, so it is impossible to continue observations for a few more months. The decision makers have to decide what to do.
Over two days in April, participants gathered at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland to consider national and global responses to the scenario.
"It was a very successful round table exercise, with close to a hundred participants from US government organizations, and for the first time planetary defense experts from around the world," said Trick Daly, the exercise's coordinator. "An asteroid impact will have several national and international consequences, so if this scenario really occurs, international cooperation will be necessary."
In real life, CNEOS calculates the trajectory of each near-Earth object to provide estimates of potential future impact hazards for NASA's Planetary Defense Program. To make this scenario realistic, the CNEOS team simulated all observations from the months leading up to the exercise and used trajectory calculations to simulate the impact probability.
"At this point in time, the impact was probable but still uncertain, and there were significant uncertainties about the size of the object and the location of the impact," said Davide Parnocchia, a navigation engineer who led the design of the asteroid's trajectory. "It was interesting to see how it affected the choices of the decision makers and how the international community might react to a real threat in 14 years."
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