NASA and its international partners are thinking the unthinkable. A tabletop exercise at the 2019 Planetary Defense Conference (PDC) next week will consider a fictional scenario where an asteroid 100 to 300 m (330 to 990 ft) in diameter with a one-in-100 chance of striking the Earth on April 29, 2027 is detected. The aim of the exercise is to develop suitable ways to respond to such an emergency.

Our world is filled with all sorts of natural disasters that take a painfully high toll in lives and property every year. In the past 100 years, governments and private agencies have become much better at responding to, and sometimes predicting, such emergencies through global rescue operations, detectors, warning systems and safeguards.

However, human progress has also made us aware of other natural threats that are highly improbable, but carry such a high risk factor that they cannot be ignored. Case in point is the danger of rogue asteroid impacts. These are very unlikely, with the chances of even a smaller one hitting the Earth set at once a century (and even then, most likely to land in an unpopulated area), but such strikes in the past may have already caused such global events as the extinction of the dinosaurs.

One frustrating thing about such rare threats is that there isn't any direct experience of them to build on. To make up for this, NASA, its Planetary Defense Coordination Office (PDCO), the European Space Agency's Space Situational Awareness-NEO Segment and the International Asteroid Warning Network (IAWN), FEMA, and others have taken to conducting periodic exercises in disaster response in addition to their ongoing search for Near-Earth Objects (NEOs) that cross the orbit of how planet.

The 2019 PDC will examine a fictional scenario written by the Jet Propulsion Laboratory's Center for NEO Studies (CNEOS). This does not involve an actual asteroid impact, but it does postulate that on March 26, 2019, a hypothetical asteroid called 2109 PDC was detected by the Minor Planet Center. The asteroid is described as very faint with a magnitude of 21.1 and a diameter of up to 300 m (990 ft).

The object is classed as a Potentially Hazardous Asteroid and on March 27 ESA and NASA's impact monitoring systems determined that it had a one in 50,000 chance of hitting the Earth in eight years and one month. On April 29, 2019, the first day of PDC, the probability raises to one in 100. This is the threshold for action as set by the international community.

The purpose of the exercise is to both develop possible responses over five days of discussion and to improve communications between the various agencies as part of the National Near-Earth Object Preparedness Strategy and Action Plan, which was published in 2018. The participants will look at how NEO observers, space agency officials, emergency managers, decision makers and citizens should respond in the face of shifting predictions and new information.

So far, there have been six similar exercises in which FEMA says it learned that emergency agencies are less interested in the science of asteroid impacts than in when, where and how an asteroid would impact, and the type and extent of damage that could occur. This means that NASA and its researchers have placed greater emphasis on ways to make more exact predictions of asteroid impacts and effects by better observations of NEO positions, orbital motions, and characteristics.

"NASA and FEMA will continue to conduct periodic exercises with a continually widening community of U.S. government agencies and international partners," says Lindley Johnson, NASA's Planetary Defense Officer. "They are a great way for us to learn how to work together and meet each other's needs and the objectives laid out in the White House National NEO Preparedness Action Plan."

Sources: NASA, ESA

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