It’s the Doomsday event that reigns supreme over all others: An asteroid, on a collision course with Earth, is discovered with very little time to prevent a possible impact.
In addition to being wonderful fodder for blockbuster movies, this scenario was also the inspiration for a tabletop exercise with NASA scientists at the International Academy of Astronautics' Planetary Defense Conference last week. The asteroid drill is a mainstay of the biennial conference, but this year was different for two reasons: 1) The event was held virtually due to the COVID-19 pandemic, and 2) the fictional 2021 asteroid could not be stopped despite the scientists’ best efforts, even with a nuclear option.
“The exercise played out that we basically had to take the hit,” said Lindley Johnson, NASA’s Planetary Defense Officer, in a call, noting that it was among the “more challenging scenarios” ever presented at the conference.
“One of the objectives of this exercise is to get the disaster management and emergency response community more involved and thinking about what they would be facing if we didn't have the time to divert an asteroid in space, and did have to take the impact somewhere,” Johnson added.
Details about this hypothetical space rock, dubbed 2021 PDC, were devised by the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory, which helpfully emphasized that the asteroid “does not exist and therefore there is no threat to Earth” in a summary of the four-day event.
On April 26, the first day of the exercise, participants learned that the asteroid was anywhere from 35 meters (100 feet) to 700 meters (2,000 feet) wide, and that it had a one-in-20 chance of impacting Earth around October 20 of this year.
While those initial 1-20 odds might sound good, the news got grim on the second day, which involved an imaginary time jump to May 2. New observations of 2021 PDC revealed that it had a 100 percent chance of hitting Europe or Northern Africa in just six months.
The extremely short notice made it impossible for the tabletop team, which involved hundreds of people, to develop and launch a mission that could deflect or disrupt the hazardous space rock in time.
“To mount a campaign, even a single mission, given our current state of the technology and how we do these deep space missions, we need a lead time, I would say, of a minimum of two years, and we’d be much more comfortable if it were five years,” Johnson said.
More bad omens emerged on day three of the simulation, which fast-forwarded to International Asteroid Day on June 30: The asteroid was predicted to crash somewhere inside the relatively populated region of central Europe.
By day four, the participants were situated within a week of impact, and discussions focused on evacuations and disaster response within the revised crash zone, south of Prague.
According to a report generated during the exercise, the deflection option wasn’t viable because it would require sending a spacecraft to nudge the asteroid off-course much further in advance of the impact than the allotted six months. The report noted that a nuclear explosive device sent to disrupt the asteroid is “the only viable mitigation option in very short warning scenarios,” but after robust calculations, that option was also ruled impractical in this instance.
As a result, the team recommended the development of rapid response spacecraft launches that could blast off within days or weeks of notice.
The projected crash site. Image: Google Earth/ International Academy of Astronautics (IAA) 2021 Planetary Defense Conference
That said, the tabletop exercise demonstrated that even worst-case scenarios still present many opportunities to mitigate casualties and damage. If that seems like cold comfort, take solace in the fact that Johnson and his colleagues are working on many projects that will further reduce the already extremely low odds that such a hazardous asteroid will threaten our civilization any time soon.
Later this year, NASA will launch the Double Asteroid Redirection Test (DART), a mission that will lay the basic groundwork for any future attempts to deflect asteroids away from trajectories that pose a threat to Earth. DART will slam into a small asteroid that is orbiting a larger asteroid, in a system known as Didymos, providing a safe way to experiment with this planetary defense strategy.
In addition, the Near-Earth Object Surveillance Mission (NEOSM), due for launch in the mid-2020s, will scan the solar system for any potentially hazardous asteroids from its perch between Earth and the Sun. Missions such as NEOSM are designed to prevent the types of imminent emergencies presented in the latest tabletop exercise by providing scientists with ample time to prepare for dangerous encounters.
“We do have the technology to find any significant impactor well in advance—years, if not decades in advance,” said Johnson. “Part of all this is to get folks to understand that the further out in time that we find a potential impactor, the bigger chance and the more possibilities we have to do something about it in space, and never have to suffer those consequences.”